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Avian communities on utility rights-of-ways and other managed shrublands in the northeastern United States
Forest Ecology and Management 185 (2003) 193–205
Avian communities on utility rights-of-ways and other managed shrublands in the northeastern United States John L. Confer*, Sarah May Pascoe Biology Department, Ithaca College, Ithaca, NY 14850, USA
Abstract We studied bird density and nesting success on utility rights-of-way (ROW) managed primarily by selective herbicide application in New York, Massachusetts and Maine. For comparison, we also estimated bird density in ROW managed by cutting in New Hampshire and New York and in shrublands managed by fire in the Finger Lakes National Forest (FLNF), New York. On herbicide-managed ROW, we detected a mean of 14.3 individuals and 12.2 species per point count, including many species of early-succession habitat that are declining throughout northeastern United States. Nesting success in forested landscapes of New York, Maine, and Massachusetts was 55% on the ROW, 69% in forests within 20 m of the ROW, and 63% in forests more than 20 m from the ROW. Brown-headed cowbirds (Molothrus ater) parasitized 5.3% of the nests and reduced host recruitment by even less. This suggests that ROW in forested areas support high production of shrubland birds and do not exert a measurably harmful effect on forest-nesting birds. Selective herbicide application on ROW sustained shrubland vegetation and supported high densities and high nesting success. Mechanical cutting lowered the structural diversity of vegetation the following spring and was associated with fewer individual birds and species. Cool burns in early spring produced a high structural diversity of herbs, shrubs and trees and supported a high density of birds and bird species. Long-term maintenance of shrublands by burning will require supplemental cutting to remove saplings. As reforestation continues to reduce shrubland habitat, probably below pre-colonial levels, active management for early-succession habitat will be necessary to sustain current population levels of numerous species. # 2003 Elsevier B.V. All rights reserved. Keywords: Succession; Shrubland birds; Rights-of-way; Habitat selection; Nesting success; Shrubland management
1. Introduction Population changes for songbirds have elicited considerable concern (Askins, 2000; Dettmers, 2003). Some have expressed concerns for the decline of forest-nesting songbirds due to deforestation in their winter habitat (Robbins et al., 1989) and others have expressed concern about forest fragmentation in the breeding grounds (e.g. Robinson et al., 1995; Hoover * Corresponding author. Tel.: þ1-607-274-3978. E-mail address: [email protected] (J.L. Confer).
et al., 1995). Yet, in general, woodland birds are doing well in northeastern United States. Data from the Breeding Bird Survey (BBS; Sauer et al., 2001) for 1980–2000 show that 57% (43 of 75) of all woodland species in northeastern United States are increasing. BBS data also show that 66% (29 of 44) of all Neotropical migrant birds in northeastern United States with significant population trends for 1980– 2000 are decreasing. The general decline of Neotropical migrants is partially due to a decline in birds associated with disturbance-generated habitats (Dettmers, 2003). This has stimulated concern for birds
0378-1127/$ – see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0378-1127(03)00255-X
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associated with grasslands and shrublands (Confer, 1992; Askins, 1993; Litvaitis et al., 1999; King and DeGraaf, 2000). In addition to species associated with early-successional habitats, many of the declining Neotropical migrants are woodland species. Of woodland species with significantly declining populations, 82% (14 of 17) use mid-successional forests, open parklands, or dense understory; and 53% (9) actually prefer disturbance conditions (according to habitat descriptions provided by the American Ornithologists’ Union (1983), Appendix A). Of the Neotropical migrants from all habitats in northeastern United States that show a significant decline from 1980 to 2000 (BBS data), 90% (26 of 29) use disturbancegenerated ecosystems broadly defined to include open fields, shrublands, mid-successional forests, open parkland and forest edge and 72% (21) prefer disturbance and non-climax habitats (Appendix B). Thus, disturbance-generated ecosystems should be a major concern for avian conservation in northeastern United States. In the state of New York, current management reduces potential beaver wetlands by two-thirds or 290,000 ha that could provide shrubland habitat (Gotie and Jenks, 1984; Anonymous, 1997). Pine barrens support shrubland birds and occurred on about 203,000 ha in pre-colonial New York but have declined by half to 100,000 ha (Cryan, 1985). Hempstead Plains was once a 20,000 ha grassland, now reduced to a token 22 ha (Askins, 2000). Blow downs occurred on 0.5% of land grant survey areas (Lorimer, 2001), extrapolated to 63,000 ha in New York. In total, disturbance habitat occurred on perhaps 730,000 ha of pre-colonial New York, about 5.7% of the surface, and have been reduced by about 410,000 ha, a loss of about 3.2% of the surface of New York. The consideration of beaver-derived shrublands makes this estimate significantly higher than the estimate of 1– 3% cover by historical shrublands in northern hardwood forests provided by (Lorimer and White, 2003). As natural disturbance ecosystems declined, anthropogenic disturbance ecosystems increased, until recently. The current acreage of successional grasslands and shrublands in New York, as estimated by the New York Natural Heritage Program, is about 372,000 ha, although this estimate is very imprecise. In New York, the rate of abandonment of farmland declined recently (Census of Agriculture, 1997), which
foretells further declines in anthropogenic shrublands. In New York, the estimate for this transient habitat is already 40,000 ha less than the historical loss of 410,000 ha of disturbance ecosystems. As the area of shrublands from abandoned farmland continues to decline, managed shrublands will become increasingly significant. Deliberately managed shrublands approximately compensate for the current loss of shrubland acreage. The New York State Department of Environmental Conservation conducted management activities for shrublands on 1389 ha in a recent year (Oehler, 2003). In New York, The Nature Conservancy manages about 1300 ha of disturbance ecosystems, the United States Forest Service manages about 600 ha and the United States Fish and Wildlife Service manages about 100 ha. In addition, shrubland habitat probably followed timber harvest on 2732 ha of New York state land in a recent 5 years span (Oehler, 2003). The area of managed disturbance ecosystems on all federal, state and non-governmental organizations in New York, excepting ROW, is about 6100 ha. In New York, the electric utilities manage about nine times this sum or about 50,000 ha of shrubland. Our paper examines changes in the abundance of birds of disturbance ecosystems with a particular focus on shrublands of early-succession. We provide a summary of the historical and contemporary changes in the availability of early-succession shrublands. We document the abundance and nesting success of shrubland birds on managed shrublands, especially on utility rights-of-way (ROW). We also examine habitat preference within the range of conditions on ROW, which resemble the early shrubland stage of old-field succession. We hope to describe conservation efforts that may help sustain the shrubland guild.
2. Methods 2.1. Bird inventories We used point counts to determine the density and diversity of birds on ROW in several study areas in the northeastern United States. Point counts were 250–350 m apart and were located on a promontory whenever possible. All count centers were located more than 100 m from roads. Count centers were located so that the vegetation was fairly uniform
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within each of four quadrants, front left, front right, back right and back left, with an orientation parallel to the length of the ROW. Only birds using the ROW were counted. Point counts were taken along eight ROW throughout Rhode Island, eight ROW distributed throughout central and eastern Massachusetts, one in each of southern and central Maine, two near Albany, NY, two in the Hudson Highlands of southern New York and two in southern New Hampshire. Point counts were also taken in the Finger Lakes National Forest (FLNF) in central New York, the only area managed by fire. In FLNF, we counted birds within a circle with 100 m radius. Although census techniques differed, qualitative differences in avian communities can be related to the different management techniques. Our count procedure gave special attention to golden-winged (Vermivora chrysoptera) and bluewinged warblers (V. pinus). The golden-winged warbler is under status assessment by the United States Fish and Wildlife Service to determine if it should be listed for protection under the Endangered Species Act. Our counts followed the protocol for The Goldenwinged Warbler Atlas Project designed by the senior author for the Laboratory of Ornithology at Cornell University. To attract almost 100% of the nearby males of these two species and their hybrids for visual identification, all of our counts lasted for 10 min while playing a tape with intermittent recordings of the songs of each species. We used BBS data to provide perspective on the regional abundance and population trends for those birds on the managed shrublands. BBS data is often described as our most reliable measure of population abundance and trends for land birds in North America (Dettmers, 2003). BBS point counts record birds detected during a 3 min period within 402 m (onefourth mile) of the count circle. We used a 10 min period and restricted our counting distance to birds 100 m up and down the length of a ROW. Howe et al. (1995) compared 10 min versus 3 min point counts in open habitats and found that 63% of the observed species were recorded during the first 3 min and our greater count duration would add more species than a BBS count. On the other hand, most of our ROW were 66–90 m in width. From the middle of a ROW, we restricted our counts to birds within 33–45 m on each side. In comparison to BBS point counts, our longer
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duration but smaller count area somewhat compensate one another. Despite differences in count techniques, large differences in frequency of detection between ROW and BBS data probably indicate true differences in relative abundance. 2.2. Nesting success Nesting success was measured in spring-summer of 2000 in three states: one ROW in each of southern and central Maine, three ROW in the watershed of Quabbin Reservoir, Massachusetts, one ROW southwest of Albany, New York, and two ROW in southern New York. We compiled data only for those species with open-cup nests. Nests were visited at least once and usually twice a week. Nests on the ground were observed by parting vegetation with a long forked stick while standing as far from the nest as possible. Above ground nests were observed with a mirror on an extendable pole. Nests were tagged at a distance of 4– 20 m from the nest. Nest success was estimated by method of Mayfield (1961, 1975) and Johnson (1979). We used 21 days as the typical duration for incubation plus nestling for the small bird species in our sample. 2.3. Analyses of habitat selection Habitat selection was estimated for the 12 species that occurred on at least 25% of the point counts and which appeared to be nesting on the ROW during the point counts. We focused our analyses of habitat selection on the proportion of cover by herbs and shrubs because management can control these parameters. Each count area was subdivided into four quadrants delineated by the middle of the ROW and a perpendicular from the count center to the ROW edge for a total of 1312 quadrants from 328 point counts. We assigned each bird to the quadrant that was used most frequently to estimate its habitat. The percent cover by herbs and shrubs was assessed visually. We assigned the percent cover to the following categories: 0–5, 6–33, 34–66 or 67–100%. After several days of practice, all members of a field crew made identical estimates at trial sites. With this procedure, field crews conducted as many as 15 point counts along 5 km of ROW in a day. This rapid inspection allowed us to obtain a large sample size, which reduced standard error and enhanced our ability
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to detect statistically significant differences in bird distribution. We used multi-factor, repeated-measures, logistic regression to evaluate the effect of each habitat characteristic, while controlling for additional factors that might influence the detection of a species (SAS Institute, 2001). Variables used in these statistical analyses were: state where counts were taken, density of herb cover, density of shrub cover, height of shrub, width of rights-of-way, observer, time of day and Julian date. Observer, time of day and Julian date each affect our detection of birds that are there, but do not affect the probability that a bird is actually there. These ‘‘nuisance’’ factors can alter the efficiency of point counts and were included in the initial statistical analyses for all species. The results were adjusted for correlation among conditions for the simultaneously recorded quadrants at each point count by use of repeated-measures analyses in the model. The following steps were used to reduce the complexity of the initial, full analysis. The initial logistic regression analysis for each species was run with all variables. ROW width and shrub height were measured only for the last 75% of the point counts so that the initial statistical analyses omitted 25% of the counts. If either the ROW width or shrub height had P-values >0.1, they were dropped and the analysis was repeated to take advantage of the larger sample size. Nuisance variables in the full statistical formulation for each species were dropped if the P-values were >0.1. Vegetation variables with P-values >0.2 were similarly eliminated and the analysis was repeated. Vegetation variables in the initial statistical formulation that were close to P ¼ 0:2, were retained for analyses in the reduced model in order to confirm that they explained insignificant amounts of variation in species presence. The ‘keep’ or ‘drop’ decisions were based on likelihood ratio statistics distributed as w2 (SAS Institute, 2001). 2.4. Management alternatives Most of our point counts were compiled on ROW maintained by selective herbicide application, the predominant management tool used by utilities in northeastern United States. This management procedure combines selective spraying or cutting and stump treatment of individual saplings, spraying of shrub
patches that might inhibit line repair and cutting of taller trees along the ROW perimeter. Near waterways, spraying is often replaced by cutting. The area around the base of support poles is cleared of all vegetation to facilitate repairs. Taller shrubs and occasionally trees are allowed to grow in depressions. Thus, management by selective herbicide application creates vegetative structure that is variable but that normally has about equal abundance of herbs and patches of shrubs. We also assessed the effects on the avian community due to management by fire and by cutting. Point counts were compiled on 600 ha of fire-managed shrubland in the Finger Lakes National Forest. The Forest Service uses relatively cool fires in early March. We compiled point counts on the Blenheim-Gilboa ROW near Albany and in southern New Hampshire in ROW maintained by cutting. Our survey of BlenheimGilboa was conducted in spring following a fall cut before significant regrowth of the woody shrubs.
3. Results During 1998–2000, we compiled 328 10 min point counts in ROW in five northeastern states. Most counts were taken in areas dominated by a mix of herbs and shrubs maintained by selective herbicide application. In 1998–2000, we obtained 157 counts in central and eastern Massachusetts on eight ROW, 24 along two ROW in southern New Hampshire, and 63 throughout Rhode Island on seven ROW maintained by New England Electric System and Eastern Utilities Associates. In 1999, we obtained 21 point counts on two ROW maintained by the New York Power Authority near Albany, NY. Eleven of these point counts were on ROW that were cut in fall 1998 and one site was sprayed. Nine point counts were taken on a ROW that has not been managed since installation, 20 years ago. Although this is not typical of ROW management, these counts are included because they contribute unique data on avian habitat selection in an older stage of succession on ROW. In 1998–1999, we obtained 38 point counts in southern New York on two ROW maintained by Orange and Rockland Utilities. During 2000, we obtained an additional 25 point counts in southern Maine on two ROW of Central Maine Power Company. In addition, we obtained 31 counts during 1998–1999 in shrubland managed by fire in FLNF.
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Table 1 Abundance and population trends for common species in ROW in northeastern US Species
No./point count
Ratio point count/BBS
Population trend northeastern US
Common yellowthroat Eastern towhee Prairie warbler Gray catbird Brown-headed cowbird American goldfinch Chestnut-sided warbler Song sparrow Field sparrow Yellow warbler American robin Common grackle (Quiscalus quiscula) Red-winged blackbird (Agelaius phoeniceus) Mourning dove (Zenaida macroura) Blue-winged warbler Cedar waxwing (Bombycilla cedororum) Black-capped chickadee (Poecile atricapillus) Blue jay (Cyanocitta cristata)
1.3 1.3 1.1 1.0 0.89 0.65 0.63 0.62 0.61 0.53 0.45 0.37 0.35 0.35 0.32 0.28 0.27 0.25
4.2 7.6 30 4.5 5.9 2.8 6.4 1.3 4.4 3.2 0.44 0.35 0.36 0.97 20 1.9 1.6 1.1
0.2 3.7 1.4 0.1 2.6 1.9 0.7 1.2 3.9 0.6 0.2 1.9 2.6 1.9 1.0 0.8 1.7 1.0
Listed species occurred on at least 25% of the point counts taken in May–June of 1998–2000. Values represent the mean number of individuals from 328 point counts obtained on 24 ROW. The ratio is derived from the mean number per point count in ROW compared to the mean number per point count for the North American Breeding Bird Survey (BBS) from 1966 to 1998 for the northeastern US. The annual population trend for northeastern US is from BBS data.
3.1. Avian populations on utility rights-of-way
3.2. Nesting success
We identified 92 species that foraged on the ROW during the counts. Most of these appeared to nest on the ROW. We observed a mean of 14.3 individual birds and 12.2 species per point count with similar results for all states. This compares favorably to a mean of 9– 11 species for 10 min point counts (n ¼ 270) for open and forest habitats, respectively, in a national forest in Wisconsin (Howe et al., 1995). Throughout the northeastern United States, the density of shrubland birds on ROW is quite high. Most of the common species nesting on ROW are declining throughout the northeast outside of the ROW (Table 1). ROW occasionally support exceptionally high concentrations of some species. As examples, in Sterling Forest State Park (SFSP) the relative abundance of prairie warblers (Dendroica discolor) and golden-winged warblers on ROW is about 200 times greater than in the state as a whole (Table 2). The high concentration of golden-winged warbler is especially notable because it is under status assessment for listing as an endangered species.
We measured nesting success of birds on ROW in heavily-forested landscapes throughout northeastern United States: the Huyck Preserve in central New York, two ROW in Sterling Forest State Park in southern New York, three ROW in Quabbin Reservoir in Massachusetts, and one ROW in both southern and central Maine. These areas were selected because extensive forests surrounded them. On these ROW and in adjacent forests, cowbird parasitism occurred in only 5.3% of the nests (12 of 226). All but one of the nests had only one cowbird egg and, without predation or abandonment, could have fledged some young of the host species. Consequently, parasitism reduced the hosts’ potential recruitment by approximately 2%. We measured nesting success on the ROW, in adjacent forests within 20 m of the ROW, and in forests >20 m from the ROW for a total of 164 nests. Results were statistically indistinguishable among the locations and were pooled. Nesting success was 55% (n ¼ 56) for nests on the ROW, 69% (n ¼ 19) for nests within 20 m of the ROW, and 63% (n ¼ 32) for forest
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Table 2 Abundance and population trends for species in ROW of Orange and Rockland Utilities within Sterling Forest State Park (SFSP) in southern New York Species
No./point count O&R ROW in SFSP
Point count ratio SFSP/BBS
Population trends New York
Prairie warbler Gray catbird Eastern towhee Common yellowthroat Yellow warbler Blue-winged warbler Golden-winged warbler Field sparrow American goldfinch Black-and-white warbler Northern oriole Brown-headed cowbird Chestnut-sided warbler American redstart (Setophaga ruticilla) Indigo bunting (Passerina cyanea) Rose-breasted grosbeak
1.5 1.2 1.0 0.90 0.89 0.71 0.68 0.58 0.53 0.47 0.47 0.42 0.42 0.32 0.32 0.24
226 4.9 11 2.3 3.0 53 201 5.4 1.4 16 3.1 2.3 3.5 3.0 2.9 2.6
5.7 0.1 6.0 0.1 0.3 1.6 5.6 4.1 1.5 1.8 0.8 2.3 0.8 1.4 0.1 1.0
Listed species utilized the ROW as part or all of their nesting territory and occurred on nearly 25% of 38 point counts taken in May–June of 1998–1999. The ratio is derived from the mean number of individuals per point count in ROW managed by selective herbicide application compared to the mean number per point count for the North American Breeding Bird Survey from 1966 to 1998 for New York. Population trends are derived from BBS data for New York.
nests over 20 m from the ROW. The nesting success rates exceed the average of 49% compiled by Nice (1957) for 7788 open-cup nests. Our sample size is small and the confidence intervals are large. Nonetheless, the estimated nesting success of 69% for the forest near the ROW suggests that the negative effects of edge observed in agricultural landscapes did not occur in this survey of ROW in forested landscapes throughout the northeast. This result is consistent with results of similar studies summarized by DeGraaf and Yamasaki (2003). 3.3. Habitat selection All habitat attributes that significantly correlated with the probability of detection were determined for 11 of the 12 most common species nesting on the ROW (Table 3). The American robin (Turdus migratorius), one of the 12 most common species, is omitted because the results are not internally consistent for inexplicable reasons. For these species, variation in the density of herbs and shrubs was associated with a two- to four-fold change in the probability of detection. Casual inspection of the vegetation on the surveyed
ROW might lead one to mistakenly consider the area as one habitat type. To these species, there are ecologically distinct habitats within the early-successional shrublands maintained on ROW. Our point counts were taken on ROW that varied from 20 to 110 m in width. The multiple, logistic regression detected a significant change in probability of detection as width varied for seven species. We have expressed the increase in probability of detection as a percentage in proportion to the change in width. If, for example, the probability of detection increased twofold as width increased two-fold, then we have expressed this response to ROW width as 100%. For the field sparrow and American goldfinch, the increase in probability of detection was proportionally greater than the increase in width. This suggests an area-sensitive response with increasing density as width increased. The brown-headed cowbird, prairie warbler, eastern towhee (Pipelo erythrophthalmus) and gray catbird (Dumatella carolinensis) had a significant increase in probability of detection as width increased, but the increase was proportionally less than the increase in width. These species appear to increase in abundance but decrease in absolute density
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Table 3 Habitat attributes that significantly affected probability of detection on utility rights-of-way in northeastern United States Species
Field sparrow Song sparrow Brown-headed cowbird Blue-winged warbler Chestnut-sided warbler Common yellowthroat Prairie warbler Yellow warbler Eastern towhee Gray catbird American goldfinch
Herb density
Dense Dense Dense Moderate to dense Slight to moderate Slight to moderate Slight Trace to slight – – –
Shrub
Response to ROW widtha (%)
Density
Height
– – –
– Tall Tall Short Short
20
Tall Short – Tall Tall
50 45 – 60 150
Low Dense Moderate Moderate to Dense Dense Dense –
115 60
Logistic regression analyses were used to determine if the probability of detection changed significantly in response to herb and shrub density, shrub height and ROW width. For species showing a significant change in probability of detection in regard to cover by herbs and shrubs, the descriptor indicates the condition associated with the attribute that provided the maximum probability of occurrence. a For species that showed a significant change in probability of detection as ROW width changed, the value is the ratio of the change in probability compared to the change in width, expressed in percent (see text).
as width increased. The song sparrow (Melospiza melodia), blue-winged warbler and common yellowthroat (Gleothypis trichas) showed no significant change in detection despite a six-fold range in width. The chestnut-sided warbler and yellow warbler had a negative response slope. These two species frequently occurred along the ROW edge and made minimal use of the middle of the ROW. On our surveys, their absolute abundance appeared to decrease as width increased.
supported the fewest individuals (mean ¼ 8:8) and species (mean ¼ 7:6). Selective herbicide application creates vegetative cover that often has about equal abundance of herbs and patches of shrubs. The sustained abundance of herbaceous growth is quite distinct from the habitat following blow downs or clear-cutting, which have an abundance of woody, tree stems. Selective herbicide application supported the greatest number of individuals (mean ¼ 12:1) and species (mean ¼ 10:3) of shrubland birds.
3.4. ROW management alternatives and the avian community 4. Discussion In FLNF, management by cool fires in spring produces structural diversity with patches of herbs and patches of shrubs and small clusters of trees. The firemaintained shrublands supported the greatest mean number of individuals (13.1) and species (15.1) per point count. Several of these were forest species, including the veery (Catharus fuscescens) and ovenbird (Seiurus aurocapillus), that never occurred on the treeless ROW. However, management by fire cannot be used in most locations and trees that survive cool burns must be cut at about 10–15 years intervals. On the Blenheim-Gilboa ROW near Albany, the vegetation had very low structural diversity in the first spring after cutting. Management on this ROW
In the northeastern United States, two-thirds of the Neotropical migrants are experiencing significant population declines (Sauer et al., 2001). Of these, over 80% use disturbance-dependent ecosystems such as grasslands, shrublands, forest edges and mid-successional forests. The decline in avian species of these ecosystems correlates with the decline in such habitats. In New York, about 60% of the historical disturbance-dependent ecosystems are gone, and Noss et al. (1995) estimated that more than half of the original ecosystems in eastern North America that have declined by over 98% are grasslands, savannas, barren communities and shrublands that are often
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maintained by disturbance. Much of the loss of disturbance-dependent ecosystems occurred many decades ago and the current decline of birds of these ecosystems is related primarily to a recent decline in anthropogenic habitats. Tens of millions of acres of farmland were abandoned in northeastern United States during the last 150 years (Census of Agriculture, 1997), much of which has passed through old-field succession and is now reforested. However, farmland abandonment ended in New England decades ago and is declining in other eastern states. One management goal for shrubland species is to restore the historical range of habitats and associated species. Although this is an admirable goal, its achievement seems impossible. As noted by Litvaitis (2003), ‘‘Managing wildlife habitats in this region will require a willingness to explore unconventional and creative solutions to overcome the challenges such circumstances present. Large portions of this region have been modified by intense development and human activity such that habitats in these areas no longer represent the range of variability that occurred prior to European settlement’’. This is illustrated by the loss of 20,000 ha of Hempstead grasslands due to the city of Hempstead Plains, only one of many examples of irreversible human development on disturbance communities. Management for the declining species of earlysuccession habitats is especially difficult because this involves so many types of habitat. The range of habitat we observed on ROW managed by selective herbicide is quite different from the range of habitats following blow downs or clear-cuts. ROW usually have a high proportion of herbs and patches of shrubs and almost no tree stems since they are selectively removed. Managed ROW resemble the stage of oldfield succession when tree stems first become visible. Clear-cuts and blow downs usually start with tens of thousands tree stems per ha and develop even higher densities in the first 5–15 years (Thompson and DeGraaf, 2001). Both the habitat on ROW and the habitat following clear-cuts are sometimes called shrublands. However, tree stem density and the bird community are quite different between ROW and clear-cuts. Comparing 23 species that appeared within 15 years after clearcutting in eastern deciduous forests (Thompson and DeGraaf, 2001) with the 18 ROW species that
occurred on at least 25% of our point counts (Table 1), only 6 species were in common. Similarly, comparing 16 species that occurred on 20% or more of the point counts in clear-cuts in northern New Hampshire (King and DeGraaf, 2000) with Table 1 species, only three species were in common. The differences between avian communities on ROW and in clearcuts provide strong support for the suggestion that shrubland species are often habitat specialists (Askins, 1993). Consequently, management for many of the early-succession bird species will require burning or spraying to establish extensive herbaceous cover. Management for those shrubland birds that utilize habitat with high densities of woody stems can be obtained by clear-cuts or blow downs. A long-term rotation of clear-cutting would support the later group of shrubland species and also provide mid-successional forests that are preferred by many of the declining woodland species (Appendix A). Some suggest that northeastern United States should be managed for the native plants and animals and the historical condition of northeastern United States (Litvaitis, 2003; Lorimer and White, 2003). Widespread reforestation on abandoned farmland and the return of habitat that resembles pre-colonial conditions in the northeast provides some plausibility to this suggestion. However, due to farmland abandonment in the northeast, humans depend on food from other regions. As a result, we in the northeast contribute to the loss of 98% of the tall grass prairie (Noss et al., 1995). Therefore, it seems inappropriate to manage the northeast exclusively for northeastern wildlife while food production for northeasterners contributes significantly to the near total destruction of the grassland biome. Management options are severely limited because the location of semi-natural ecosystems available for management and areas of man-dominated ecosystems are all highly clumped and inequitably distributed across the United States. Because most of the precolonial shrubland habitat is irreversibly gone due to permanent human development, management for these species and for biodiversity cannot be done on most of the historical shrubland sites. Management for shrublands in many locations must suppress natural reforestation. In the context of largely forested landscapes in the northeast, the exchange of forest acreage for shrublands
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is a net gain for regional biodiversity. Our surveys on ROWadd to the evidence that shrubland–forest edges in extensively forested regions will not lower nesting success for birds, although clearly the edge effect is detrimental to forest species in agricultural areas (Robinson et al., 1995). Management involving a long-term rotation of treatment could support earlysuccessional species and would also support forest species that use parklands, edges and mid-successional forests, many of which are now declining.
Acknowledgements Orange and Rockland Utilities, New England Electric System Companies, later named National Grid USA, Central Maine Power Company, the Electric Power Research Institute and New York State Electric and Gas helped fund these studies. Assistance was
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provided by Peter Simpson, Todd McLeish, Weston Davis, Mark Beamish, John Goodrich-Mahoney, Kevin McLoughlin, Richard Mider and Margaret Degasser and particularly Steve Grandinali and Tom Sullivan. Part of this survey was conducted in and supported by the Edmund Miles Huyck Preserve in Rensselaerville, NY, Inc. with assistance from Dr. Rick Wyman, Director and Vern Husik. New York State Department of Parks, Recreation and Historic Preservation permitted this study in Sterling Forest State Park with the assistance of Tom Lyons. The National Forest Service funded surveys in Finger Lakes National Forest with guidance by Clayton Grove. These studies were also funded by a grant from the National Fish and Wildlife Federation, the Clinton Ford Fund and the Dana Scholarship Fund. The incredible effort of numerous field assistants provided the backbone of this work. Peter Wrege provided the statistical analyses.
Appendix A Habitat use by significantly declining, woodland birds in US. Fish and Wildlife Region 5. Annual population trends determined from North American Breeding Bird Survey data for 1980–2000 (Sauer et al., 2001). The preference, use or avoidance of non-climax, breeding habitat with disturbance, edge or parkland attributes derived from AOU Checklist (1998) and Holmes and Sherry (2001). Information on forest interior species is from Therres (1992). Species
Decline (%)
Preference, use or avoidance of non-climax habitats
Forest interior
Habitat description
Tennessee warbler
8.2
Prefers
No
Cape may warbler
7.3
Uses
No
Eastern screech-owl
6.7
Prefers
No
Olive-sided flycatcher
6.2
Uses and may prefer
No
‘‘Coniferous and deciduous woodland (usually open, with brushy undergrowth and herbaceous ground cover), alder and willow thickets (especially in west), edges of bogs, and open deciduous second-growth; . . ..’’ AOU ‘‘Primarily spruce forest, usually in open stands and often mixed with other trees, spruce bogs; . . ..’’ AOU ‘‘Open woodland, deciduous forest, open mixed deciduous–coniferous woodland, parklands; . . ..’’ AOU ‘‘Taiga, subalpine coniferous forest, spruce bogs, burns, and mixed coniferous-deciduous forest with standing dead trees; . . ..’’ AOU
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Appendix A. (Continued ) Species
Decline (%)
Preference, use or avoidance of non-climax habitats
Forest interior
Habitat description
Black-billed cuckoo
6.1
Prefers
No
Canada warbler
3.3
Prefers
No
Eastern wood-pewee
2.8
Uses and may prefer
No
Yellow-billed cuckoo
2.8
Prefers
No
Kentucky warbler
2.4
Uses and may prefer
Yes
Wood thrush
2.2
Prefers
Yes
Rose-breasted grosbeak
2.0
Prefers
No
Least flycatcher
1.6
Prefers
No
Black-and-white warbler 1.4
Avoids
Yes
Scarlet tanager
1.3
Avoids
Yes
Veery
1.3
Prefers
Yes
Great crested flycatcher
0.9
Uses and may prefer
No
Acadian flycatcher
0.8
Avoids
Yes
‘‘Forest edge and open woodland, both deciduous and coniferous, with dense deciduous thickets: . . ..’’ AOU ‘‘Moist woodland with dense undergrowth (especially aspen-popular), bogs, and tall scrub along streams; . . ..’’ AOU ‘‘Deciduous or mixed deciduous– coniferous forest, forest edge, open woodland, and parks; . . ..’’ AOU ‘‘Open woodland, especially where undergrowth is thick, parks and riparian woodland; . . ..’’ AOU ‘‘Humid deciduous forest with dense undergrowth, dense second-growth, shady ravines and swamp edges; . . ..’’ AOU ‘‘. . . strongly associated with midsuccessional forests . . ..’’ Holmes and Sherry ‘‘Open deciduous forest and forest edge (especially poplar and aspen), woodland, and tall second-growth; . . ..’’ AOU ‘‘ . . . strongly associated with mid-successional forests . . ..’’ Holmes and Sherry ‘‘Extensive tracts of deciduous and mixed deciduous–coniferous forest and woodland, primarily where tall trees present; . . ..’’ AOU ‘‘Deciduous forest and mature deciduous woodland, especially where oaks common, less frequently in mixed deciduous–coniferous forest; . . ..’’ AOU ‘‘Poplar, aspen, or swampy forest, especially in more open areas with shrubby understory, also in second-growth, willow or alder thickets near water; . . ..’’ AOU ‘‘Breeds in deciduous and evergreen broadleaf forest, including open woodland, parks and orchards; . . ..’’ AOU ‘‘Breeds in humid deciduous forest; northerly populations prefer moist ravines, often with hemlocks; . . ..’’ AOU
Appendix B Habitat use by significantly declining, Neotropical migrant birds in US. Fish and Wildlife Region 5. Annual population trends determined from North American Breeding Bird Survey data for 1980–2000 (Sauer et al., 2001). The preference, use or avoidance of non-climax, breeding habitat with early to mid-succession, disturbance, edge or parkland attributes derived from AOU Checklist (1998) and Holmes and Sherry (2001). Information on forest interior species is from Therres (1992). Preference, use or avoidance of non-climax habitats
Forest interior
Habitat description
Tennessee warbler (Vermivora peregrina) Cape may warbler (Dendroica tigrina) Black-billed cuckoo (Coccyzus erythropthalmus) Olive-sided flycatcher (Contopus cooperi) Golden-winged Warbler
7.4 5.9 5.8 5.8 4.2
Prefers Uses Prefers Uses and may prefer Prefers
No No No No No
Grasshopper sparrow (Ammodramus savannarum) 3.4
Prefers
No
Canada warbler (Wilsonia canadensis) Bank swallow (Riparia riparia)
3.2 3.1
Prefers Prefers
Yes No
Eastern wood-pewee (Contopus virens) Yellow-billed cuckoo (Coccyzus americanus) Barn swallow (Hirundo rustica)
2.8 2.7 2.4
Uses and may prefer Prefers Prefers
No No No
Kentucky warbler Common nighthawk (Chordeiles minor)
2.4 2.2
Uses and may prefer Prefers
Yes No
Prefers Prefers Prefers
Yes No No
As in Appendix A As in Appendix A As in Appendix A As in Appendix A ‘‘Second-growth dominated by shrubs and dense herbaceous growth, from overgrown fields to forest edge, bogs: . . ..’’ AOU ‘‘Prairie, old-fields, open grasslands, cultivated fields, and savanna.’’ AOU As in Appendix A Habitat not part of successional gradient, but is non-climax As in Appendix A As in Appendix A ‘‘Open situations, less frequently in partly open habitats, frequently near water; . . ..’’ AOU As in Appendix A ‘‘A wide variety of open and semi-open situations, especially in savanna, grasslands, fields, and around human habitation, including cities and towns; frequently nests on flat gravel roofs of buildings.’’ AOU As in Appendix A As in Appendix A ‘‘Breeds in open country with scattered trees and shrubs, including cultivated land with hedgerows; . . ..’’ AOU
Wood thrush (Hylocichla mustelina) 2.2 Rose-breasted grosbeak (Pheucticus ludovicianus) 2.0 Eastern kingbird (Tyranus tyrannus) 1.7
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Decline (%)
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Species
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Appendix B. (Continued) Decline (%)
Preference, use or avoidance of non-climax habitats
Forest interior
Habitat description
Least flycatcher (Empidonax minimus) Indigo bunting (Passerina amoena)
1.6 1.4
Prefers Prefers
No No
Black-and-white warbler (Mniotilta taria) Scarlet tanager (Piranga olivacea) Veery (Catharus fuscecens) Chimney swift (Chaetura pelagica)
1.4 1.3 1.3 1.1
Avoids Avoids Prefers Prefers
Yes Yes Yes No
Yellow-breasted chat (Icteria virens)
1.0
Prefers
No
Great crested flycatcher (Myiarchus crinitus) Baltimore oriole (Icterus galbula)
0.9 0.9
Uses and may prefer Prefers
No No
Acadian flycatcher (Empidonax virescens) Chipping sparrow (Spizella passerina)
0.8 0.6
Avoids Prefers
Yes No
Common yellowthroat
0.6
Prefers
No
House wren (Troglodytes aedon)
0.6
Prefers
No
As in Appendix A ‘‘Deciduous forest edge and regenerating clearings, open woodland, second-growth, shrubby areas, scrub, and riparian woodland; . . ..’’ AOU As in Appendix A As in Appendix A As in Appendix A ‘‘Open situations and woodland, especially around human habitation; now nests primarily in chimneys, originally on cliffs or in hollow trees.’’ AOU ‘‘Dense second-growth, riparian thickets, and brush.’’ AOU As in Appendix A ‘‘Breeds in open woodland, deciduous forest edge, riparian woodland, orchards and planted shade trees.’’ AOU As in Appendix A ‘‘Open coniferous forest (especially early second-growth) and forest edge (especially pine), oak woodland, pine–oak association, and open woodland and parks: . . ..’’ AOU ‘‘Marshes (especially cattail), thickets near water, bogs, brushy pastures, old-fields, and, locally, undergrowth at edge of humid forest; . . ..’’AOU ‘‘Thickets and scrub in partly open situations, open woodland (especially aspen), farmlands, chaparral, riparian woodland, and around human habitations [aedon group]: . . ..’’AOU
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Species
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References American Ornithologists’ Union, 1983. Check-list of North American Birds, seventh ed. American Ornithologists’ Union, Washington, DC, USA. Anonymous, 1997. The 1996 Update on New York State’s Beaver Management Program. NYS Department of Environmental Conservation. Askins, R.A., 1993. Population trends in grassland, shrubland, and forest birds in eastern North America. Curr. Ornithol. 11, 1–34. Askins, R.A., 2000. Restoring North American Birds: Lessons from Landscape Ecology. Yale University Press, New Haven. Confer, J.L., 1992. Golden-winged warbler, Vermivora chrysoptera. In: Schneider, K.J., Pence, D.M. (Eds.), Migratory Nongame Birds of Management Concern in the Northeast. United States Department of Interior, Fish and Wildlife Services, Newton Corners, MA. Census of Agriculture, 1997. United States Department of Agriculture. Washington, DC, USA. DeGraaf, R.M., Yamasaki, M., 2003. Options for managing earlysuccession forests and shrublands northeastern United States. For. Ecol. Manage. 185, 179–191. Cryan, J.F., 1985. Retreat in the barrens. Defenders 60, 18–29. Dettmers, R., 2003. Status and conservation of shrubland birds in the northeastern United States. For. Ecol. Manage. 185, 81–93. Gotie, R., Jenks, D., 1984. Assessment of the use of wetlands inventory maps for determining potential beaver habitat. NYS Fish Game J. 31, 55–62. Holmes, R.T., Sherry, T.W., 2001. Thirty-year bird population trends in an unfragmented temperate deciduous forest: importance of habitat change. Auk 118, 589–610. Hoover, J.P., Brittingham, M.C., Goodrich, L.J., 1995. Effects of forest patch size on nesting success of wood thrushes. Auk 112, 146–155. Howe, R.W., Wolf, A.T., Rinaldi, T., 1995. Monitoring birds in a regional landscape: lessons from the Nicolet National Forest Bird Survey. In: Ralph, C.J., Sauer, J.R., Droege, S. (Eds.), Monitoring Bird Populations by Point Counts. Gen. Tech. Rep. PSW-GTR-149, Pacific Southwest Research Station, Forest Service, United States Department of Agriculture, Albany, CA, pp. 83–92, 187 pp. Johnson, D.H., 1979. Estimating nest success: the Mayfield method and an alternative. Auk 96, 651–661. King, D.I., DeGraaf, R.M., 2000. Bird species diversity and nesting
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success in mature, clearcut and shelterwood forest in northern New Hampshire, USA. For. Ecol. Manage. 129, 227–235. Litvaitis, J.A., 2003. Are pre-Columbian conditions relevant baselines for managed forests in the northeastern United States? For. Ecol. Manage. 185, 113–126. Litvaitis, J.A., Wagner, D.L., Confer, J.L., Tarr, M.D., Snyder, E.J., 1999. Early successional forests and shrub-dominated habitats: land-use artifact or critical community in the northeastern United States. Northeast Wildlife 54, 101–118. Lorimer, C.G., 2001. Historical and ecological roles of disturbance in eastern North American forests: 9000 years of change. Wildlife Soc. Bull. 29, 425–439. Lorimer, C.G., White, A.S., 2003. Scale and frequency of natural disturbance in the northeastern United States: implications for early successional forest habitat and regional age distribution. For. Ecol. Manage. 185, 41–64. Mayfield, H., 1961. Nesting success calculated from exposure. Wilson Bull. 73, 255–261. Mayfield, H., 1975. Suggestions for calculating nest success. Wilson Bull. 87, 456–466. Nice, M.M., 1957. Nesting success in altricial birds. Auk 74, 305–321. Noss, R.F., LaRoe, E.T., Scott, J.M., 1995. Endangered Ecosystems of the United States: A Preliminary Assessment of Loss and Degradation. Biological Report 28, National Biological Service, Washington, DC, USA. Robbins, C.S., Sauer, J.R., Greenberg, R., Droege, S., 1989. Population declines in North American birds that migrate to the neotropics. Proc. Natl. Acad. Sci. U.S.A. 86, 7658–7662. Robinson, S.K., Thompson III, F.R., Donovan, T.M., Whitehead, D.R., Faaborg, J., 1995. Regional forest fragmentation and the nesting success of birds. Science 267, 1987–1990. SAS Institute, 2001. SAS/STAT, Version 6.11. SAS Institute Inc., Cary, NC. Sauer, J.R., Hines, J.E., Fallon, J., 2001. The North American Breeding Bird Survey, Results and Analysis 1966–2000, Version 2001.2. USGS Patuxent Wildlife Research Center, Laurel, MD. Therres, G.D., 1992. Integrating management of forest interior migratory birds with game in the northeast. In: Finch, D.M, Stangel, P.W. (Eds.), Status and Management of Neotropical Migratory Birds. Gen. Tech. Rep. RM-229, USDA Forest Service, pp. 402–407. Thompson III, F.R., DeGraaf, R.M., 2001. Conservation approaches for woody, early successional communities in the eastern United States. Wildlife Soc. Bull. 29, 483–494.
Avian communities on utility rights-of-ways and other managed shrublands in the northeastern United States John L. Confer*, Sarah May Pascoe Biology Department, Ithaca College, Ithaca, NY 14850, USA
Abstract We studied bird density and nesting success on utility rights-of-way (ROW) managed primarily by selective herbicide application in New York, Massachusetts and Maine. For comparison, we also estimated bird density in ROW managed by cutting in New Hampshire and New York and in shrublands managed by fire in the Finger Lakes National Forest (FLNF), New York. On herbicide-managed ROW, we detected a mean of 14.3 individuals and 12.2 species per point count, including many species of early-succession habitat that are declining throughout northeastern United States. Nesting success in forested landscapes of New York, Maine, and Massachusetts was 55% on the ROW, 69% in forests within 20 m of the ROW, and 63% in forests more than 20 m from the ROW. Brown-headed cowbirds (Molothrus ater) parasitized 5.3% of the nests and reduced host recruitment by even less. This suggests that ROW in forested areas support high production of shrubland birds and do not exert a measurably harmful effect on forest-nesting birds. Selective herbicide application on ROW sustained shrubland vegetation and supported high densities and high nesting success. Mechanical cutting lowered the structural diversity of vegetation the following spring and was associated with fewer individual birds and species. Cool burns in early spring produced a high structural diversity of herbs, shrubs and trees and supported a high density of birds and bird species. Long-term maintenance of shrublands by burning will require supplemental cutting to remove saplings. As reforestation continues to reduce shrubland habitat, probably below pre-colonial levels, active management for early-succession habitat will be necessary to sustain current population levels of numerous species. # 2003 Elsevier B.V. All rights reserved. Keywords: Succession; Shrubland birds; Rights-of-way; Habitat selection; Nesting success; Shrubland management
1. Introduction Population changes for songbirds have elicited considerable concern (Askins, 2000; Dettmers, 2003). Some have expressed concerns for the decline of forest-nesting songbirds due to deforestation in their winter habitat (Robbins et al., 1989) and others have expressed concern about forest fragmentation in the breeding grounds (e.g. Robinson et al., 1995; Hoover * Corresponding author. Tel.: þ1-607-274-3978. E-mail address: [email protected] (J.L. Confer).
et al., 1995). Yet, in general, woodland birds are doing well in northeastern United States. Data from the Breeding Bird Survey (BBS; Sauer et al., 2001) for 1980–2000 show that 57% (43 of 75) of all woodland species in northeastern United States are increasing. BBS data also show that 66% (29 of 44) of all Neotropical migrant birds in northeastern United States with significant population trends for 1980– 2000 are decreasing. The general decline of Neotropical migrants is partially due to a decline in birds associated with disturbance-generated habitats (Dettmers, 2003). This has stimulated concern for birds
0378-1127/$ – see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0378-1127(03)00255-X
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associated with grasslands and shrublands (Confer, 1992; Askins, 1993; Litvaitis et al., 1999; King and DeGraaf, 2000). In addition to species associated with early-successional habitats, many of the declining Neotropical migrants are woodland species. Of woodland species with significantly declining populations, 82% (14 of 17) use mid-successional forests, open parklands, or dense understory; and 53% (9) actually prefer disturbance conditions (according to habitat descriptions provided by the American Ornithologists’ Union (1983), Appendix A). Of the Neotropical migrants from all habitats in northeastern United States that show a significant decline from 1980 to 2000 (BBS data), 90% (26 of 29) use disturbancegenerated ecosystems broadly defined to include open fields, shrublands, mid-successional forests, open parkland and forest edge and 72% (21) prefer disturbance and non-climax habitats (Appendix B). Thus, disturbance-generated ecosystems should be a major concern for avian conservation in northeastern United States. In the state of New York, current management reduces potential beaver wetlands by two-thirds or 290,000 ha that could provide shrubland habitat (Gotie and Jenks, 1984; Anonymous, 1997). Pine barrens support shrubland birds and occurred on about 203,000 ha in pre-colonial New York but have declined by half to 100,000 ha (Cryan, 1985). Hempstead Plains was once a 20,000 ha grassland, now reduced to a token 22 ha (Askins, 2000). Blow downs occurred on 0.5% of land grant survey areas (Lorimer, 2001), extrapolated to 63,000 ha in New York. In total, disturbance habitat occurred on perhaps 730,000 ha of pre-colonial New York, about 5.7% of the surface, and have been reduced by about 410,000 ha, a loss of about 3.2% of the surface of New York. The consideration of beaver-derived shrublands makes this estimate significantly higher than the estimate of 1– 3% cover by historical shrublands in northern hardwood forests provided by (Lorimer and White, 2003). As natural disturbance ecosystems declined, anthropogenic disturbance ecosystems increased, until recently. The current acreage of successional grasslands and shrublands in New York, as estimated by the New York Natural Heritage Program, is about 372,000 ha, although this estimate is very imprecise. In New York, the rate of abandonment of farmland declined recently (Census of Agriculture, 1997), which
foretells further declines in anthropogenic shrublands. In New York, the estimate for this transient habitat is already 40,000 ha less than the historical loss of 410,000 ha of disturbance ecosystems. As the area of shrublands from abandoned farmland continues to decline, managed shrublands will become increasingly significant. Deliberately managed shrublands approximately compensate for the current loss of shrubland acreage. The New York State Department of Environmental Conservation conducted management activities for shrublands on 1389 ha in a recent year (Oehler, 2003). In New York, The Nature Conservancy manages about 1300 ha of disturbance ecosystems, the United States Forest Service manages about 600 ha and the United States Fish and Wildlife Service manages about 100 ha. In addition, shrubland habitat probably followed timber harvest on 2732 ha of New York state land in a recent 5 years span (Oehler, 2003). The area of managed disturbance ecosystems on all federal, state and non-governmental organizations in New York, excepting ROW, is about 6100 ha. In New York, the electric utilities manage about nine times this sum or about 50,000 ha of shrubland. Our paper examines changes in the abundance of birds of disturbance ecosystems with a particular focus on shrublands of early-succession. We provide a summary of the historical and contemporary changes in the availability of early-succession shrublands. We document the abundance and nesting success of shrubland birds on managed shrublands, especially on utility rights-of-way (ROW). We also examine habitat preference within the range of conditions on ROW, which resemble the early shrubland stage of old-field succession. We hope to describe conservation efforts that may help sustain the shrubland guild.
2. Methods 2.1. Bird inventories We used point counts to determine the density and diversity of birds on ROW in several study areas in the northeastern United States. Point counts were 250–350 m apart and were located on a promontory whenever possible. All count centers were located more than 100 m from roads. Count centers were located so that the vegetation was fairly uniform
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within each of four quadrants, front left, front right, back right and back left, with an orientation parallel to the length of the ROW. Only birds using the ROW were counted. Point counts were taken along eight ROW throughout Rhode Island, eight ROW distributed throughout central and eastern Massachusetts, one in each of southern and central Maine, two near Albany, NY, two in the Hudson Highlands of southern New York and two in southern New Hampshire. Point counts were also taken in the Finger Lakes National Forest (FLNF) in central New York, the only area managed by fire. In FLNF, we counted birds within a circle with 100 m radius. Although census techniques differed, qualitative differences in avian communities can be related to the different management techniques. Our count procedure gave special attention to golden-winged (Vermivora chrysoptera) and bluewinged warblers (V. pinus). The golden-winged warbler is under status assessment by the United States Fish and Wildlife Service to determine if it should be listed for protection under the Endangered Species Act. Our counts followed the protocol for The Goldenwinged Warbler Atlas Project designed by the senior author for the Laboratory of Ornithology at Cornell University. To attract almost 100% of the nearby males of these two species and their hybrids for visual identification, all of our counts lasted for 10 min while playing a tape with intermittent recordings of the songs of each species. We used BBS data to provide perspective on the regional abundance and population trends for those birds on the managed shrublands. BBS data is often described as our most reliable measure of population abundance and trends for land birds in North America (Dettmers, 2003). BBS point counts record birds detected during a 3 min period within 402 m (onefourth mile) of the count circle. We used a 10 min period and restricted our counting distance to birds 100 m up and down the length of a ROW. Howe et al. (1995) compared 10 min versus 3 min point counts in open habitats and found that 63% of the observed species were recorded during the first 3 min and our greater count duration would add more species than a BBS count. On the other hand, most of our ROW were 66–90 m in width. From the middle of a ROW, we restricted our counts to birds within 33–45 m on each side. In comparison to BBS point counts, our longer
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duration but smaller count area somewhat compensate one another. Despite differences in count techniques, large differences in frequency of detection between ROW and BBS data probably indicate true differences in relative abundance. 2.2. Nesting success Nesting success was measured in spring-summer of 2000 in three states: one ROW in each of southern and central Maine, three ROW in the watershed of Quabbin Reservoir, Massachusetts, one ROW southwest of Albany, New York, and two ROW in southern New York. We compiled data only for those species with open-cup nests. Nests were visited at least once and usually twice a week. Nests on the ground were observed by parting vegetation with a long forked stick while standing as far from the nest as possible. Above ground nests were observed with a mirror on an extendable pole. Nests were tagged at a distance of 4– 20 m from the nest. Nest success was estimated by method of Mayfield (1961, 1975) and Johnson (1979). We used 21 days as the typical duration for incubation plus nestling for the small bird species in our sample. 2.3. Analyses of habitat selection Habitat selection was estimated for the 12 species that occurred on at least 25% of the point counts and which appeared to be nesting on the ROW during the point counts. We focused our analyses of habitat selection on the proportion of cover by herbs and shrubs because management can control these parameters. Each count area was subdivided into four quadrants delineated by the middle of the ROW and a perpendicular from the count center to the ROW edge for a total of 1312 quadrants from 328 point counts. We assigned each bird to the quadrant that was used most frequently to estimate its habitat. The percent cover by herbs and shrubs was assessed visually. We assigned the percent cover to the following categories: 0–5, 6–33, 34–66 or 67–100%. After several days of practice, all members of a field crew made identical estimates at trial sites. With this procedure, field crews conducted as many as 15 point counts along 5 km of ROW in a day. This rapid inspection allowed us to obtain a large sample size, which reduced standard error and enhanced our ability
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to detect statistically significant differences in bird distribution. We used multi-factor, repeated-measures, logistic regression to evaluate the effect of each habitat characteristic, while controlling for additional factors that might influence the detection of a species (SAS Institute, 2001). Variables used in these statistical analyses were: state where counts were taken, density of herb cover, density of shrub cover, height of shrub, width of rights-of-way, observer, time of day and Julian date. Observer, time of day and Julian date each affect our detection of birds that are there, but do not affect the probability that a bird is actually there. These ‘‘nuisance’’ factors can alter the efficiency of point counts and were included in the initial statistical analyses for all species. The results were adjusted for correlation among conditions for the simultaneously recorded quadrants at each point count by use of repeated-measures analyses in the model. The following steps were used to reduce the complexity of the initial, full analysis. The initial logistic regression analysis for each species was run with all variables. ROW width and shrub height were measured only for the last 75% of the point counts so that the initial statistical analyses omitted 25% of the counts. If either the ROW width or shrub height had P-values >0.1, they were dropped and the analysis was repeated to take advantage of the larger sample size. Nuisance variables in the full statistical formulation for each species were dropped if the P-values were >0.1. Vegetation variables with P-values >0.2 were similarly eliminated and the analysis was repeated. Vegetation variables in the initial statistical formulation that were close to P ¼ 0:2, were retained for analyses in the reduced model in order to confirm that they explained insignificant amounts of variation in species presence. The ‘keep’ or ‘drop’ decisions were based on likelihood ratio statistics distributed as w2 (SAS Institute, 2001). 2.4. Management alternatives Most of our point counts were compiled on ROW maintained by selective herbicide application, the predominant management tool used by utilities in northeastern United States. This management procedure combines selective spraying or cutting and stump treatment of individual saplings, spraying of shrub
patches that might inhibit line repair and cutting of taller trees along the ROW perimeter. Near waterways, spraying is often replaced by cutting. The area around the base of support poles is cleared of all vegetation to facilitate repairs. Taller shrubs and occasionally trees are allowed to grow in depressions. Thus, management by selective herbicide application creates vegetative structure that is variable but that normally has about equal abundance of herbs and patches of shrubs. We also assessed the effects on the avian community due to management by fire and by cutting. Point counts were compiled on 600 ha of fire-managed shrubland in the Finger Lakes National Forest. The Forest Service uses relatively cool fires in early March. We compiled point counts on the Blenheim-Gilboa ROW near Albany and in southern New Hampshire in ROW maintained by cutting. Our survey of BlenheimGilboa was conducted in spring following a fall cut before significant regrowth of the woody shrubs.
3. Results During 1998–2000, we compiled 328 10 min point counts in ROW in five northeastern states. Most counts were taken in areas dominated by a mix of herbs and shrubs maintained by selective herbicide application. In 1998–2000, we obtained 157 counts in central and eastern Massachusetts on eight ROW, 24 along two ROW in southern New Hampshire, and 63 throughout Rhode Island on seven ROW maintained by New England Electric System and Eastern Utilities Associates. In 1999, we obtained 21 point counts on two ROW maintained by the New York Power Authority near Albany, NY. Eleven of these point counts were on ROW that were cut in fall 1998 and one site was sprayed. Nine point counts were taken on a ROW that has not been managed since installation, 20 years ago. Although this is not typical of ROW management, these counts are included because they contribute unique data on avian habitat selection in an older stage of succession on ROW. In 1998–1999, we obtained 38 point counts in southern New York on two ROW maintained by Orange and Rockland Utilities. During 2000, we obtained an additional 25 point counts in southern Maine on two ROW of Central Maine Power Company. In addition, we obtained 31 counts during 1998–1999 in shrubland managed by fire in FLNF.
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Table 1 Abundance and population trends for common species in ROW in northeastern US Species
No./point count
Ratio point count/BBS
Population trend northeastern US
Common yellowthroat Eastern towhee Prairie warbler Gray catbird Brown-headed cowbird American goldfinch Chestnut-sided warbler Song sparrow Field sparrow Yellow warbler American robin Common grackle (Quiscalus quiscula) Red-winged blackbird (Agelaius phoeniceus) Mourning dove (Zenaida macroura) Blue-winged warbler Cedar waxwing (Bombycilla cedororum) Black-capped chickadee (Poecile atricapillus) Blue jay (Cyanocitta cristata)
1.3 1.3 1.1 1.0 0.89 0.65 0.63 0.62 0.61 0.53 0.45 0.37 0.35 0.35 0.32 0.28 0.27 0.25
4.2 7.6 30 4.5 5.9 2.8 6.4 1.3 4.4 3.2 0.44 0.35 0.36 0.97 20 1.9 1.6 1.1
0.2 3.7 1.4 0.1 2.6 1.9 0.7 1.2 3.9 0.6 0.2 1.9 2.6 1.9 1.0 0.8 1.7 1.0
Listed species occurred on at least 25% of the point counts taken in May–June of 1998–2000. Values represent the mean number of individuals from 328 point counts obtained on 24 ROW. The ratio is derived from the mean number per point count in ROW compared to the mean number per point count for the North American Breeding Bird Survey (BBS) from 1966 to 1998 for the northeastern US. The annual population trend for northeastern US is from BBS data.
3.1. Avian populations on utility rights-of-way
3.2. Nesting success
We identified 92 species that foraged on the ROW during the counts. Most of these appeared to nest on the ROW. We observed a mean of 14.3 individual birds and 12.2 species per point count with similar results for all states. This compares favorably to a mean of 9– 11 species for 10 min point counts (n ¼ 270) for open and forest habitats, respectively, in a national forest in Wisconsin (Howe et al., 1995). Throughout the northeastern United States, the density of shrubland birds on ROW is quite high. Most of the common species nesting on ROW are declining throughout the northeast outside of the ROW (Table 1). ROW occasionally support exceptionally high concentrations of some species. As examples, in Sterling Forest State Park (SFSP) the relative abundance of prairie warblers (Dendroica discolor) and golden-winged warblers on ROW is about 200 times greater than in the state as a whole (Table 2). The high concentration of golden-winged warbler is especially notable because it is under status assessment for listing as an endangered species.
We measured nesting success of birds on ROW in heavily-forested landscapes throughout northeastern United States: the Huyck Preserve in central New York, two ROW in Sterling Forest State Park in southern New York, three ROW in Quabbin Reservoir in Massachusetts, and one ROW in both southern and central Maine. These areas were selected because extensive forests surrounded them. On these ROW and in adjacent forests, cowbird parasitism occurred in only 5.3% of the nests (12 of 226). All but one of the nests had only one cowbird egg and, without predation or abandonment, could have fledged some young of the host species. Consequently, parasitism reduced the hosts’ potential recruitment by approximately 2%. We measured nesting success on the ROW, in adjacent forests within 20 m of the ROW, and in forests >20 m from the ROW for a total of 164 nests. Results were statistically indistinguishable among the locations and were pooled. Nesting success was 55% (n ¼ 56) for nests on the ROW, 69% (n ¼ 19) for nests within 20 m of the ROW, and 63% (n ¼ 32) for forest
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Table 2 Abundance and population trends for species in ROW of Orange and Rockland Utilities within Sterling Forest State Park (SFSP) in southern New York Species
No./point count O&R ROW in SFSP
Point count ratio SFSP/BBS
Population trends New York
Prairie warbler Gray catbird Eastern towhee Common yellowthroat Yellow warbler Blue-winged warbler Golden-winged warbler Field sparrow American goldfinch Black-and-white warbler Northern oriole Brown-headed cowbird Chestnut-sided warbler American redstart (Setophaga ruticilla) Indigo bunting (Passerina cyanea) Rose-breasted grosbeak
1.5 1.2 1.0 0.90 0.89 0.71 0.68 0.58 0.53 0.47 0.47 0.42 0.42 0.32 0.32 0.24
226 4.9 11 2.3 3.0 53 201 5.4 1.4 16 3.1 2.3 3.5 3.0 2.9 2.6
5.7 0.1 6.0 0.1 0.3 1.6 5.6 4.1 1.5 1.8 0.8 2.3 0.8 1.4 0.1 1.0
Listed species utilized the ROW as part or all of their nesting territory and occurred on nearly 25% of 38 point counts taken in May–June of 1998–1999. The ratio is derived from the mean number of individuals per point count in ROW managed by selective herbicide application compared to the mean number per point count for the North American Breeding Bird Survey from 1966 to 1998 for New York. Population trends are derived from BBS data for New York.
nests over 20 m from the ROW. The nesting success rates exceed the average of 49% compiled by Nice (1957) for 7788 open-cup nests. Our sample size is small and the confidence intervals are large. Nonetheless, the estimated nesting success of 69% for the forest near the ROW suggests that the negative effects of edge observed in agricultural landscapes did not occur in this survey of ROW in forested landscapes throughout the northeast. This result is consistent with results of similar studies summarized by DeGraaf and Yamasaki (2003). 3.3. Habitat selection All habitat attributes that significantly correlated with the probability of detection were determined for 11 of the 12 most common species nesting on the ROW (Table 3). The American robin (Turdus migratorius), one of the 12 most common species, is omitted because the results are not internally consistent for inexplicable reasons. For these species, variation in the density of herbs and shrubs was associated with a two- to four-fold change in the probability of detection. Casual inspection of the vegetation on the surveyed
ROW might lead one to mistakenly consider the area as one habitat type. To these species, there are ecologically distinct habitats within the early-successional shrublands maintained on ROW. Our point counts were taken on ROW that varied from 20 to 110 m in width. The multiple, logistic regression detected a significant change in probability of detection as width varied for seven species. We have expressed the increase in probability of detection as a percentage in proportion to the change in width. If, for example, the probability of detection increased twofold as width increased two-fold, then we have expressed this response to ROW width as 100%. For the field sparrow and American goldfinch, the increase in probability of detection was proportionally greater than the increase in width. This suggests an area-sensitive response with increasing density as width increased. The brown-headed cowbird, prairie warbler, eastern towhee (Pipelo erythrophthalmus) and gray catbird (Dumatella carolinensis) had a significant increase in probability of detection as width increased, but the increase was proportionally less than the increase in width. These species appear to increase in abundance but decrease in absolute density
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Table 3 Habitat attributes that significantly affected probability of detection on utility rights-of-way in northeastern United States Species
Field sparrow Song sparrow Brown-headed cowbird Blue-winged warbler Chestnut-sided warbler Common yellowthroat Prairie warbler Yellow warbler Eastern towhee Gray catbird American goldfinch
Herb density
Dense Dense Dense Moderate to dense Slight to moderate Slight to moderate Slight Trace to slight – – –
Shrub
Response to ROW widtha (%)
Density
Height
– – –
– Tall Tall Short Short
20
Tall Short – Tall Tall
50 45 – 60 150
Low Dense Moderate Moderate to Dense Dense Dense –
115 60
Logistic regression analyses were used to determine if the probability of detection changed significantly in response to herb and shrub density, shrub height and ROW width. For species showing a significant change in probability of detection in regard to cover by herbs and shrubs, the descriptor indicates the condition associated with the attribute that provided the maximum probability of occurrence. a For species that showed a significant change in probability of detection as ROW width changed, the value is the ratio of the change in probability compared to the change in width, expressed in percent (see text).
as width increased. The song sparrow (Melospiza melodia), blue-winged warbler and common yellowthroat (Gleothypis trichas) showed no significant change in detection despite a six-fold range in width. The chestnut-sided warbler and yellow warbler had a negative response slope. These two species frequently occurred along the ROW edge and made minimal use of the middle of the ROW. On our surveys, their absolute abundance appeared to decrease as width increased.
supported the fewest individuals (mean ¼ 8:8) and species (mean ¼ 7:6). Selective herbicide application creates vegetative cover that often has about equal abundance of herbs and patches of shrubs. The sustained abundance of herbaceous growth is quite distinct from the habitat following blow downs or clear-cutting, which have an abundance of woody, tree stems. Selective herbicide application supported the greatest number of individuals (mean ¼ 12:1) and species (mean ¼ 10:3) of shrubland birds.
3.4. ROW management alternatives and the avian community 4. Discussion In FLNF, management by cool fires in spring produces structural diversity with patches of herbs and patches of shrubs and small clusters of trees. The firemaintained shrublands supported the greatest mean number of individuals (13.1) and species (15.1) per point count. Several of these were forest species, including the veery (Catharus fuscescens) and ovenbird (Seiurus aurocapillus), that never occurred on the treeless ROW. However, management by fire cannot be used in most locations and trees that survive cool burns must be cut at about 10–15 years intervals. On the Blenheim-Gilboa ROW near Albany, the vegetation had very low structural diversity in the first spring after cutting. Management on this ROW
In the northeastern United States, two-thirds of the Neotropical migrants are experiencing significant population declines (Sauer et al., 2001). Of these, over 80% use disturbance-dependent ecosystems such as grasslands, shrublands, forest edges and mid-successional forests. The decline in avian species of these ecosystems correlates with the decline in such habitats. In New York, about 60% of the historical disturbance-dependent ecosystems are gone, and Noss et al. (1995) estimated that more than half of the original ecosystems in eastern North America that have declined by over 98% are grasslands, savannas, barren communities and shrublands that are often
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maintained by disturbance. Much of the loss of disturbance-dependent ecosystems occurred many decades ago and the current decline of birds of these ecosystems is related primarily to a recent decline in anthropogenic habitats. Tens of millions of acres of farmland were abandoned in northeastern United States during the last 150 years (Census of Agriculture, 1997), much of which has passed through old-field succession and is now reforested. However, farmland abandonment ended in New England decades ago and is declining in other eastern states. One management goal for shrubland species is to restore the historical range of habitats and associated species. Although this is an admirable goal, its achievement seems impossible. As noted by Litvaitis (2003), ‘‘Managing wildlife habitats in this region will require a willingness to explore unconventional and creative solutions to overcome the challenges such circumstances present. Large portions of this region have been modified by intense development and human activity such that habitats in these areas no longer represent the range of variability that occurred prior to European settlement’’. This is illustrated by the loss of 20,000 ha of Hempstead grasslands due to the city of Hempstead Plains, only one of many examples of irreversible human development on disturbance communities. Management for the declining species of earlysuccession habitats is especially difficult because this involves so many types of habitat. The range of habitat we observed on ROW managed by selective herbicide is quite different from the range of habitats following blow downs or clear-cuts. ROW usually have a high proportion of herbs and patches of shrubs and almost no tree stems since they are selectively removed. Managed ROW resemble the stage of oldfield succession when tree stems first become visible. Clear-cuts and blow downs usually start with tens of thousands tree stems per ha and develop even higher densities in the first 5–15 years (Thompson and DeGraaf, 2001). Both the habitat on ROW and the habitat following clear-cuts are sometimes called shrublands. However, tree stem density and the bird community are quite different between ROW and clear-cuts. Comparing 23 species that appeared within 15 years after clearcutting in eastern deciduous forests (Thompson and DeGraaf, 2001) with the 18 ROW species that
occurred on at least 25% of our point counts (Table 1), only 6 species were in common. Similarly, comparing 16 species that occurred on 20% or more of the point counts in clear-cuts in northern New Hampshire (King and DeGraaf, 2000) with Table 1 species, only three species were in common. The differences between avian communities on ROW and in clearcuts provide strong support for the suggestion that shrubland species are often habitat specialists (Askins, 1993). Consequently, management for many of the early-succession bird species will require burning or spraying to establish extensive herbaceous cover. Management for those shrubland birds that utilize habitat with high densities of woody stems can be obtained by clear-cuts or blow downs. A long-term rotation of clear-cutting would support the later group of shrubland species and also provide mid-successional forests that are preferred by many of the declining woodland species (Appendix A). Some suggest that northeastern United States should be managed for the native plants and animals and the historical condition of northeastern United States (Litvaitis, 2003; Lorimer and White, 2003). Widespread reforestation on abandoned farmland and the return of habitat that resembles pre-colonial conditions in the northeast provides some plausibility to this suggestion. However, due to farmland abandonment in the northeast, humans depend on food from other regions. As a result, we in the northeast contribute to the loss of 98% of the tall grass prairie (Noss et al., 1995). Therefore, it seems inappropriate to manage the northeast exclusively for northeastern wildlife while food production for northeasterners contributes significantly to the near total destruction of the grassland biome. Management options are severely limited because the location of semi-natural ecosystems available for management and areas of man-dominated ecosystems are all highly clumped and inequitably distributed across the United States. Because most of the precolonial shrubland habitat is irreversibly gone due to permanent human development, management for these species and for biodiversity cannot be done on most of the historical shrubland sites. Management for shrublands in many locations must suppress natural reforestation. In the context of largely forested landscapes in the northeast, the exchange of forest acreage for shrublands
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is a net gain for regional biodiversity. Our surveys on ROWadd to the evidence that shrubland–forest edges in extensively forested regions will not lower nesting success for birds, although clearly the edge effect is detrimental to forest species in agricultural areas (Robinson et al., 1995). Management involving a long-term rotation of treatment could support earlysuccessional species and would also support forest species that use parklands, edges and mid-successional forests, many of which are now declining.
Acknowledgements Orange and Rockland Utilities, New England Electric System Companies, later named National Grid USA, Central Maine Power Company, the Electric Power Research Institute and New York State Electric and Gas helped fund these studies. Assistance was
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provided by Peter Simpson, Todd McLeish, Weston Davis, Mark Beamish, John Goodrich-Mahoney, Kevin McLoughlin, Richard Mider and Margaret Degasser and particularly Steve Grandinali and Tom Sullivan. Part of this survey was conducted in and supported by the Edmund Miles Huyck Preserve in Rensselaerville, NY, Inc. with assistance from Dr. Rick Wyman, Director and Vern Husik. New York State Department of Parks, Recreation and Historic Preservation permitted this study in Sterling Forest State Park with the assistance of Tom Lyons. The National Forest Service funded surveys in Finger Lakes National Forest with guidance by Clayton Grove. These studies were also funded by a grant from the National Fish and Wildlife Federation, the Clinton Ford Fund and the Dana Scholarship Fund. The incredible effort of numerous field assistants provided the backbone of this work. Peter Wrege provided the statistical analyses.
Appendix A Habitat use by significantly declining, woodland birds in US. Fish and Wildlife Region 5. Annual population trends determined from North American Breeding Bird Survey data for 1980–2000 (Sauer et al., 2001). The preference, use or avoidance of non-climax, breeding habitat with disturbance, edge or parkland attributes derived from AOU Checklist (1998) and Holmes and Sherry (2001). Information on forest interior species is from Therres (1992). Species
Decline (%)
Preference, use or avoidance of non-climax habitats
Forest interior
Habitat description
Tennessee warbler
8.2
Prefers
No
Cape may warbler
7.3
Uses
No
Eastern screech-owl
6.7
Prefers
No
Olive-sided flycatcher
6.2
Uses and may prefer
No
‘‘Coniferous and deciduous woodland (usually open, with brushy undergrowth and herbaceous ground cover), alder and willow thickets (especially in west), edges of bogs, and open deciduous second-growth; . . ..’’ AOU ‘‘Primarily spruce forest, usually in open stands and often mixed with other trees, spruce bogs; . . ..’’ AOU ‘‘Open woodland, deciduous forest, open mixed deciduous–coniferous woodland, parklands; . . ..’’ AOU ‘‘Taiga, subalpine coniferous forest, spruce bogs, burns, and mixed coniferous-deciduous forest with standing dead trees; . . ..’’ AOU
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Appendix A. (Continued ) Species
Decline (%)
Preference, use or avoidance of non-climax habitats
Forest interior
Habitat description
Black-billed cuckoo
6.1
Prefers
No
Canada warbler
3.3
Prefers
No
Eastern wood-pewee
2.8
Uses and may prefer
No
Yellow-billed cuckoo
2.8
Prefers
No
Kentucky warbler
2.4
Uses and may prefer
Yes
Wood thrush
2.2
Prefers
Yes
Rose-breasted grosbeak
2.0
Prefers
No
Least flycatcher
1.6
Prefers
No
Black-and-white warbler 1.4
Avoids
Yes
Scarlet tanager
1.3
Avoids
Yes
Veery
1.3
Prefers
Yes
Great crested flycatcher
0.9
Uses and may prefer
No
Acadian flycatcher
0.8
Avoids
Yes
‘‘Forest edge and open woodland, both deciduous and coniferous, with dense deciduous thickets: . . ..’’ AOU ‘‘Moist woodland with dense undergrowth (especially aspen-popular), bogs, and tall scrub along streams; . . ..’’ AOU ‘‘Deciduous or mixed deciduous– coniferous forest, forest edge, open woodland, and parks; . . ..’’ AOU ‘‘Open woodland, especially where undergrowth is thick, parks and riparian woodland; . . ..’’ AOU ‘‘Humid deciduous forest with dense undergrowth, dense second-growth, shady ravines and swamp edges; . . ..’’ AOU ‘‘. . . strongly associated with midsuccessional forests . . ..’’ Holmes and Sherry ‘‘Open deciduous forest and forest edge (especially poplar and aspen), woodland, and tall second-growth; . . ..’’ AOU ‘‘ . . . strongly associated with mid-successional forests . . ..’’ Holmes and Sherry ‘‘Extensive tracts of deciduous and mixed deciduous–coniferous forest and woodland, primarily where tall trees present; . . ..’’ AOU ‘‘Deciduous forest and mature deciduous woodland, especially where oaks common, less frequently in mixed deciduous–coniferous forest; . . ..’’ AOU ‘‘Poplar, aspen, or swampy forest, especially in more open areas with shrubby understory, also in second-growth, willow or alder thickets near water; . . ..’’ AOU ‘‘Breeds in deciduous and evergreen broadleaf forest, including open woodland, parks and orchards; . . ..’’ AOU ‘‘Breeds in humid deciduous forest; northerly populations prefer moist ravines, often with hemlocks; . . ..’’ AOU
Appendix B Habitat use by significantly declining, Neotropical migrant birds in US. Fish and Wildlife Region 5. Annual population trends determined from North American Breeding Bird Survey data for 1980–2000 (Sauer et al., 2001). The preference, use or avoidance of non-climax, breeding habitat with early to mid-succession, disturbance, edge or parkland attributes derived from AOU Checklist (1998) and Holmes and Sherry (2001). Information on forest interior species is from Therres (1992). Preference, use or avoidance of non-climax habitats
Forest interior
Habitat description
Tennessee warbler (Vermivora peregrina) Cape may warbler (Dendroica tigrina) Black-billed cuckoo (Coccyzus erythropthalmus) Olive-sided flycatcher (Contopus cooperi) Golden-winged Warbler
7.4 5.9 5.8 5.8 4.2
Prefers Uses Prefers Uses and may prefer Prefers
No No No No No
Grasshopper sparrow (Ammodramus savannarum) 3.4
Prefers
No
Canada warbler (Wilsonia canadensis) Bank swallow (Riparia riparia)
3.2 3.1
Prefers Prefers
Yes No
Eastern wood-pewee (Contopus virens) Yellow-billed cuckoo (Coccyzus americanus) Barn swallow (Hirundo rustica)
2.8 2.7 2.4
Uses and may prefer Prefers Prefers
No No No
Kentucky warbler Common nighthawk (Chordeiles minor)
2.4 2.2
Uses and may prefer Prefers
Yes No
Prefers Prefers Prefers
Yes No No
As in Appendix A As in Appendix A As in Appendix A As in Appendix A ‘‘Second-growth dominated by shrubs and dense herbaceous growth, from overgrown fields to forest edge, bogs: . . ..’’ AOU ‘‘Prairie, old-fields, open grasslands, cultivated fields, and savanna.’’ AOU As in Appendix A Habitat not part of successional gradient, but is non-climax As in Appendix A As in Appendix A ‘‘Open situations, less frequently in partly open habitats, frequently near water; . . ..’’ AOU As in Appendix A ‘‘A wide variety of open and semi-open situations, especially in savanna, grasslands, fields, and around human habitation, including cities and towns; frequently nests on flat gravel roofs of buildings.’’ AOU As in Appendix A As in Appendix A ‘‘Breeds in open country with scattered trees and shrubs, including cultivated land with hedgerows; . . ..’’ AOU
Wood thrush (Hylocichla mustelina) 2.2 Rose-breasted grosbeak (Pheucticus ludovicianus) 2.0 Eastern kingbird (Tyranus tyrannus) 1.7
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Decline (%)
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Species
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Appendix B. (Continued) Decline (%)
Preference, use or avoidance of non-climax habitats
Forest interior
Habitat description
Least flycatcher (Empidonax minimus) Indigo bunting (Passerina amoena)
1.6 1.4
Prefers Prefers
No No
Black-and-white warbler (Mniotilta taria) Scarlet tanager (Piranga olivacea) Veery (Catharus fuscecens) Chimney swift (Chaetura pelagica)
1.4 1.3 1.3 1.1
Avoids Avoids Prefers Prefers
Yes Yes Yes No
Yellow-breasted chat (Icteria virens)
1.0
Prefers
No
Great crested flycatcher (Myiarchus crinitus) Baltimore oriole (Icterus galbula)
0.9 0.9
Uses and may prefer Prefers
No No
Acadian flycatcher (Empidonax virescens) Chipping sparrow (Spizella passerina)
0.8 0.6
Avoids Prefers
Yes No
Common yellowthroat
0.6
Prefers
No
House wren (Troglodytes aedon)
0.6
Prefers
No
As in Appendix A ‘‘Deciduous forest edge and regenerating clearings, open woodland, second-growth, shrubby areas, scrub, and riparian woodland; . . ..’’ AOU As in Appendix A As in Appendix A As in Appendix A ‘‘Open situations and woodland, especially around human habitation; now nests primarily in chimneys, originally on cliffs or in hollow trees.’’ AOU ‘‘Dense second-growth, riparian thickets, and brush.’’ AOU As in Appendix A ‘‘Breeds in open woodland, deciduous forest edge, riparian woodland, orchards and planted shade trees.’’ AOU As in Appendix A ‘‘Open coniferous forest (especially early second-growth) and forest edge (especially pine), oak woodland, pine–oak association, and open woodland and parks: . . ..’’ AOU ‘‘Marshes (especially cattail), thickets near water, bogs, brushy pastures, old-fields, and, locally, undergrowth at edge of humid forest; . . ..’’AOU ‘‘Thickets and scrub in partly open situations, open woodland (especially aspen), farmlands, chaparral, riparian woodland, and around human habitations [aedon group]: . . ..’’AOU
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Species
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