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Benefits of rotational grazing and dense nesting cover for island-nesting waterfowl in southern Quebec
Agriculture, Ecosystems and Environment 78 (2000) 261–272
Benefits of rotational grazing and dense nesting cover for island-nesting waterfowl in southern Quebec Stéphane Lapointea,1 , Jean-François Giroux a,∗ , Luc Bélanger b , Bernard Filion c a
Département des sciences biologiques, Université du Québec à Montréal, C.P. 8888, Succursale Centre-ville, Montréal, Québec, Canada H3C 3P8 b Environment Canada, Canadian Wildlife Service, 1141 route de l’Église, C.P. 10100, Ste-Foy, Québec, Canada G1V 4H5 c Ducks Unlimited Canada, 710 rue Bouvier, suite 260, Québec, Canada G2J 1A7 Received 7 July 1998; received in revised form 9 August 1999; accepted 29 September 1999
Abstract Intensification of agricultural practices is an important factor responsible for the decline of duck populations throughout North America. More than 200 islands covering a total of 5000 ha are found in the St. Lawrence river between Montreal and Trois-Rivieres in southern Quebec. The value of these islands as duck nesting habitat, however, is often limited by cattle grazing. The effects of two types of habitat improvements, rotational grazing and establishment of dense nesting cover (DNC), on island-nesting waterfowl was studied from 1992 to 1994. Four treatments were compared: idle fields with no vegetation improvement but exclusion of cattle, improved pastures with seeding of forage plants for cattle, DNC fields with improved cover for ducks and exclusion of cattle and unimproved pastures used after the duck nesting season. Before habitat improvements, grazing by cattle reduced dry mass of green vegetation by 53% relative to ungrazed plots. No difference was found in the biomass of live (green) and dead (residual) vegetation among the islands’ sections before treatments. Nest density and the number of expected nests based on the area covered by each habitat were also similar among sections before treatment. Gadwall (Anas strepera L.), mallard (Anas platyrhynchos L.), and pintail (Anas acuta L.) were the most abundant species nesting on the islands and this was not affected by treatments. Two years after habitat improvements, the number of duck nests increased. Idle fields and 2-year old DNC had greater visual obstruction, more residual vegetation and more litter. Densities of 2.8 and 7.0 nests ha−1 with 69 and 82% Mayfield nest success were recorded in the idle and DNC fields, respectively. Nest success was low in improved pasture where a large proportion of nests were trampled (33%) or depredated (28%). Fencing permitted growth of emergent vegetation which enabled over-water nesting by ducks. These results indicate that with appropriate management, coexistence of cattle and nesting waterfowl is possible on islands of the St. Lawrence river. ©2000 Elsevier Science B.V. All rights reserved. Keywords: Ducks; Nesting density; Nesting success; Rotational grazing; DNC; Quebec
1. Introduction ∗ Corresponding author. Tel.: +1-514-987-3000 (ext. 3353); fax: +1-514-987-4647. E-mail address: [email protected] (J.-F. Giroux). 1 Present address: Pharmascience inc, 6111 Royalmount Avenue, suite 100, Montr´eal, Qu´ebec, Canada H4P 2T4.
Expansion of farming and changes to more intensive agricultural practices are among the most important factors responsible for the decline of duck populations throughout North America (Sugden and Beyersber-
0167-8809/00/$ – see front matter ©2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 8 8 0 9 ( 9 9 ) 0 0 1 3 2 - 2
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gen, 1984). Ducks now have to nest in the remaining small and fragmented habitats where predation is often higher than in contiguous habitats (Clark and Nudds, 1991; Pasitschniak-Arts and Messier, 1995). Even though dabbling duck populations have less declined in eastern than in western North America, biologists are concerned with the rate at which wetlands and their surroundings are being converted into farmlands and industrial lands (Anonymous, 1986). They are therefore seeking ways to overcome loss of natural habitats. Island construction is one of the most productive techniques because ducks can nest at higher densities and with better success attributed to lower mammalian predation (Giroux, 1981; Duebbert, 1982). However, island construction is expensive and could be inappropriate where duck populations are low (Lokemoen, 1984; Bélanger and Tremblay, 1989). Managing existing islands may therefore be a more cost-efficient strategy (Lokemoen and Woodward, 1992). In Quebec, the most productive areas for nesting dabbling ducks are located on islands of the St. Lawrence river. More than 200 islands ranging in size from <0.1 to >2000 ha and representing nearly 5000 ha of land are found between Montreal and Trois-Rivieres. However, the value of these islands for ground-nesting birds is often limited by cattle grazing (Bélanger and Lehoux, 1995; Bélanger and Picard, 1999). This reduces the screening effect of vegetative cover, which can lower nest density and success (Lokemoen et al., 1990; Gilbert et al., 1996; Kruse and Bowen, 1996). Grazing can also affect residual vegetation, an important component of nesting cover for early nesting ducks (Duebbert, 1969; Kirsh, 1969; Kirsh et al., 1978). It may provide ideal temperature and humidity for better egg hatchability (Francis, 1968; Duebbert, 1969). In addition, grazing and trampling of shoreline vegetation decrease over-water nesting (Krapu et al., 1979; Kirby et al., 1992). Finally, trampling of eggs by cattle directly affects nest success (Jensen et al., 1990). Studies have shown that it is possible to reduce the adverse effects of cattle with rotational grazing systems (Gjersing, 1975; Barker et al., 1990). Pastures are divided into smaller range units and cattle are periodically moved among these units (Kie et al., 1994). Rotation of cattle throughout the growing season maintains plants at a vegetative stage that provides the most digestible forage (Conrad and Martz,
1985). Thus, higher stocking rates are possible and calf weight gain per hectare is better than with continuous grazing (Barker et al., 1990). Furthermore, this leaves more undisturbed cover for nesting waterfowl because less area is required for cattle. The establishment of dense nesting cover (DNC) has also been proposed to enhance duck productivity because it generally supports higher nest densities and success (Duebbert and Kantrud, 1974; Klett et al., 1988; but see McKinnon and Duncan, 1999 for different results). Improved nesting cover is easy and less expensive to establish and can be sown on islands where cover is inadequate (Lokemoen, 1984; Willms and Crawford, 1989). Several years, however, may be needed before cover becomes adequate for nesting (Livezey, 1981). The effectiveness of rotational grazing systems and cover improvements on nesting waterfowl has been generally demonstrated in the mid continent of North America. This area is characterized by productive wetlands called prairie potholes that support large numbers of breeding ducks (Bellrose, 1979). On the other hand, little is known about the effects of these techniques in eastern North America where wetlands are often located along rivers or coastal shores and where breeding populations of ducks are less numerous than in the mid continent. Moreover, growing conditions are different between the dryer prairie region and eastern North America and this could affect the establishment of seeded vegetation. The objective of this study was therefore to evaluate the effectiveness of rotational grazing systems and cover improvements to enhance nesting habitat for waterfowl in eastern North America. More specifically, the aims were to compare different grassland management practices on (1) quality of nesting cover, (2) nest density of dabbling ducks and (3) their nesting success on islands of the St. Lawrence river in southern Quebec.
2. Material and methods 2.1. Study area The study was conducted between 1992 and 1994 on four adjacent islands near Varennes, Quebec, Canada (45◦ 400 N, 73◦ 270 W), 16 km northeast of Montreal along the St. Lawrence river. The climate is
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continental temperate, with a mean annual temperature of 6.1◦ C and a total annual rainfall of 768 mm. The islands ranged in size between 9.4 and 59.8 ha for a total of 111.5 ha. No trees or shrubs were present. As water levels recede following spring run-off, the islands are joined together forming small interior marshes with stands of cattail (Typha angustifolia L.), big burreed (Sparganium eurycarpum Engelm) and arrowhead (Sagittaria spp.). Cattle were brought to the islands by boat in late May to early June and removed in November. A total of 114, 100 and 85 cows were present in 1992, 1993 and 1994, respectively. During the first year, cattle grazed everywhere on the islands (Fig. 1).
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Ile-aux-Fermiers, Masta and St. Patrice islands were dominated by red-top (Agrostis alba L.), red fescue-grass (Festuca rubra L.), Kentucky bluegrass (Poa pratensis L.) and cow vetch (Vicia cracca L.). Grande-Ile was covered with reed canary grass (Phalaris arundinacea L.) and Canada reed-grass (Calamagrostis canadensis [Michx.] Beauv.). In August 1992, Ducks Unlimited Canada seeded DNC, improved the quality and quantity of forage of some pastures and set up a series of electric fences to establish a rotational grazing system. The forage on Grande-Ile was improved by sowing 19.2 ha of timothy (Phleum pratense L.), sweet clover (Melilotus officinalis [L.] Desr.), smooth brome (Bromus
Fig. 1. Location of the treatments on islands at Varennes, Quebec, 1992–1994.
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inermis Leyss.) and clover (Trifolium spp.). Mixtures of reed canary grass in association with timothy, tall fescue-grass (Festuca elatior L.), Orchard grass (Dactylis glomerata L.) or tall wheat grass (Agropyron elongatum [Host] Beauv.) were sown on 5 ha on Grande-Ile to establish the DNC. Non-selective herbicide (glyphosate) was applied to treated fields before cultivation. Masta, St. Patrice as well as parts of Grande-Ile and Ile-aux-Fermiers were left idle with no grazing. Interior marshes were also protected from cattle by permanent or temporary fences. In 1993, a rotational grazing system was established (Fig. 1). From the end of May to mid July, cattle were restricted to the improved pasture. After the duck nesting season, they were moved to the unimproved pasture on Ile-aux-Fermiers until mid September. Another rotation between these two pastures took place between mid September and the end of October. Finally, cattle were allowed to graze freely on all islands (including in DNC) for 2 weeks until they were removed in mid November. During the duck nesting period from May to July, there were four treatments: idle field (59.9 ha), improved pasture with cattle (19.2 ha), unimproved pasture without cattle (27.4 ha) and a 1-year old DNC (DNC93: 5.0 ha). In the fall of 1993, another 9.4 and 5.6 ha of DNC were established on St. Patrice and Grande-Ile, respectively, by sowing Western wheat grass (Agropyron smithii Rydb.) and crested wheat grass (Agropyron cristatum[L.] Gaertn.). A portion of Ile-aux-Fermiers was ploughed so it could be converted to improved pasture but was not seeded on time. This pasture was therefore a ploughed field (17.6 ha) during the 1994 duck nesting season. The other treatments included: idle field (39.1 ha), improved pasture with cattle (19.2 ha), unimproved pasture without cattle (15.6 ha), a 1-year old DNC (DNC94: 15.0 ha) and a 2-year old DNC (DNC93: 5.0 ha). Rotation of cattle among pastures in 1994 was similar to the previous year.
2.2. Cover evaluation In 1992, the effect of cattle grazing on the vegetation was evaluated by establishing 50 0.5 m × 1.0 m exclosures that were randomly located on the four islands and put in place before the arrival of cattle. In July, all the vegetation above 1 cm was clipped in a
10 cm × 10 cm randomly selected quadrat within each exclosure and in grazed sites, also located randomly at more than 50 m away from the exclosures. Vegetation was sorted into live biomass defined as any green plants or plant parts, and residual vegetation that consisted of dead biomass from the previous and current years. Vegetation was then dried to constant weight in a micro-wave oven (Bilanski and Ghate, 1978) and weighed to the nearest 0.1 g. Data from unfenced plots were also used to compare live and dead biomass of vegetation among treatments before and after the management. In 1993, the same 50 plots were used while in 1994 an additional 39 plots were randomly located, for a total of 89. Sampling was conducted during the first week of July each year, using the same procedure. In 1994, visual obstruction readings were taken every 10 m along a 100 m NE–SW line in each plot using a Robel et al. (1970) pole. Readings were taken at a distance of 4 m from a height of 1 m. These readings give an index of cover quality by taking into account height and density of vegetation; it is highly corelated to biomass (Robel et al., 1970). Depth of residual vegetation accumulated on the ground was measured at the same time with a ruler (±0.5 cm). Visual obstruction and litter depth readings were taken every 2 weeks from early May to mid July.
2.3. Nest search Nest searches were conducted three times each year at 3-week intervals starting at the end of May. All upland habitats on the islands were searched for waterfowl nests. In 1994, newly established patches of emergent vegetation were also searched for nests by walking through the vegetation. Searches were done between 06:00 and 12:00 hours when most females are attending their nests (Gloutney et al., 1993). Four to eight observers walked side-by-side along transects, making noise and beating vegetation with 2.5 m bamboo sticks in order to flush nesting females. We consider that nest detection probability was equivalent among treatments characterized by herbaceous cover without shrubs. Species was determined by identifying the flushing female or using egg and down characteristics. Nest location was marked with 1 m long bamboo sticks in 1992 and 1993, and with reed-grass (Phragmites communis Trin.) stalks in 1994. Markers were
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placed 4 m NE of the nest. Semi-rigid plastic poles were used as nest markers in pastures in 1993 and 1994 because bamboo sticks proved to be inadequate markers when cattle were present (most of them fell in 1992). Nest locations were also marked on 1 : 10 000 aerial color photographs. A nest was defined as a bowl containing at least one egg. Number of eggs, amount of down and incubation stage evaluated by floatation (Westerskov, 1950) were recorded at each visit. Nests were revisited during the following nest search or after the expected hatching date. A nest was considered successful if at least one egg hatched. Unsuccessful nests were recorded as depredated if there was evidence of broken or missing eggs, abandoned if the nest was not tended by a female and had cold eggs, and trampled if the clutch and the surrounding area were destroyed by cattle hooves. Predators were identified when possible following the criteria of Rearden (1951) based on remaining eggshells and/or characteristics of the nests. 2.4. Costs of habitat improvements For each treatment, costs of ground preparation (tillage, harrowing, seeding and spreading of herbicides and fertilizers), chemical products, seeds and fencing were evaluated. Costs for ground preparation were obtained from Le Comité des références économiques en agriculture du Québec (1994) and do not represent the actual costs involved during the study because some operations were done on an experimental basis and were therefore more costly than regular operations. Seed prices are from Labon. All prices are in 1997 CDN dollars. 2.5. Data analyses Paired t-tests were used to evaluate the effect of cattle grazing by comparing biomass between ungrazed and grazed plots. Comparisons among treatments or sampling periods for live and dead biomass, visual obstruction and litter depth were made using analyses of variance (ANOVAs). Homogeneity of variances and normality were verified and logarithmic transformations were applied when necessary. When a significant effect was found, Tukey multiple comparison tests were performed to determine where differences occurred.
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Annual differences in the species composition of the breeding population were compared with χ 2 tests as well as the proportion of early, intermediate and late nests in each treatment. Comparisons of expected and observed distributions of nests among treatments were made using χ 2 . The proportion of the nesting population (expected numbers of nests) in each treatment was weighed proportional to the area covered by each habitat. For each year, contrast tests were used to determine where differences occurred among treatments. In 1994, nest success was calculated for each treatment using the Mayfield-40% method followed by pairwise comparisons of daily survival rates among treatments (Johnson, 1979). For all analyses, significance level was fixed at P = 0.05 and all means are shown ±1 SE. 3. Results 3.1. Nesting cover In July 1992, before any habitat improvements, grazing by cattle reduced live biomass by 53% (ungrazed plots: 671 ± 50 g m−2 ; grazed plots: 355 ± 37 g m−2 ; t47 = 5.88, P < 0.0001). However, there was more dead biomass (residual vegetation) in grazed than in ungrazed plots (122 ± 81 versus 81 ± 68 g m−2 ; t47 = 3.1, P = 0.004). In terms of cover quality, no difference among treatments was recorded for live (F3,46 = 2.08, P = 0.12) and dead biomass (F3,46 = 0.65, P = 0.59) in 1992 before the management (Table 1). In 1993, after fencing and DNC seeding, there was significantly more live biomass in DNC93 than in improved pasture (F3,46 = 3.38, P = 0.03). In 1994, DNC93 had more live biomass than all other treatments (F5,78 = 5.77, P < 0.0001). Finally, DNC93 and idle field also had more residual vegetation than improved pasture, DNC94 and ploughed field (F5,78 = 11.85, P < 0.0001). From May to July, the visual obstruction index increased in every treatment during the summer of 1994, except in improved pastures where it decreased after the arrival of cattle (Fig. 2; idle: F5,96 = 48.9; improved pastures: F5,138 = 46.8; unimproved pastures: F5,54 = 10.1; DNC93 fields: F5,24 = 11.3; DNC94 fields: F5,71 = 19.9; ploughed fields: F5,108 = 16.9,
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Table 1 Live and dead aboveground biomass (g m−2 dry mass) of vegetation used as nesting cover by ducks measured in July in six treatments on islands at Varennes, Quebec, 1992–1994 Treatment
na
1992b
1993
Live Idle field Improved pasture Unimproved pasture DNC93d DNC94d Ploughed
23, 23, 17 12, 12, 24 11, 10, 10 4, 5, 5 –, –, 13 –, –, 19
Dead
433 ± 60 212 ± 53 a 396 ± 90 a 369 ± 105 a – – ac
126 ± 14 130 ± 21 119 ± 37 77 ± 13 – –
a a a a
1994
Live
Dead
Live
Dead
577 ± 85 ab 419 ± 127 b 808 ± 155 ab 830 ± 198 a – –
86 ± 18 a 134 ± 51 a 207 ± 69 a 132 ± 96 a – –
780 ± 135 b 366 ± 71 b 632 ± 70 b 1631 ± 700 a 614 ± 130 b 327 ± 94 b
217 ± 40 a 50 ± 12 b 103 ± 24 ab 222 ± 82 a 24 ± 9 b 14 ± 6 b
a
Number of plots sampled in 1992, 1993 and 1994, respectively. Vegetation was sampled before establishment of treatments. c Means (±1 SE) followed by the same letters within a column are not significantly different (P > 0.05). d DNC93 and DNC94 refer to the dense nesting cover treatments established in 1993 and 1994, respectively. b
P < 0.0001, for all tests). Idle field and DNC93 had higher visual obstruction than improved pasture in early May (F5,82 = 20.79, P < 0.0001) and the difference remained significant between DNC93 and improved pasture throughout the summer (P < 0.0001).
Litter depth decreased during the summer but differences were only significant in idle fields (F5,96 = 3.38, P = 0.007), improved pastures (F5,138 = 27.3, P < 0.0001) and ploughed fields (F5,108 = 2.35, P = 0.05). Idle fields and DNC93 had more litter than improved
Fig. 2. Visual obstruction index measured with the Robel et al. (1970) pole and litter depth in six treatments during the summer 1994 on islands at Varennes, Quebec. Significant differences among treatments for each period are indicated by different letters (P < 0.05).
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Table 2 Species composition (%) of duck nests initiated on the islands at Varennes, Quebec, 1992–1994
Table 4 Number of duck nests per hectare in six treatments on islands at Varennes, Quebec, 1992–1994
Species
Year
Gadwall Mallard Pintail Shoveler American Wigeon Othersa
Year (number of nests) 1992 (139)
1993 (137)
1994 (254)
24 25 24 10 10 6
28 20 27 9 7 9
32 26 18 14 8 2
Treatment Idle Improved Unimproved DNC93a DNC94a Ploughed field pasture pasture
1992b 1.0 1993 1.5 1994 2.8
a Included American black duck (Anas rubripes Brewster), blue-winged teal (Anas discors L.), redhead (Aythya americana) and unidentified species.
pastures throughout the summer (P < 0.0001) while DNC94 and the ploughed fields had a very thin litter (Fig. 2). 3.2. Number of nests and species composition A total of 143, 143 and 263 duck nests were found in the upland portions of the islands during the 300, 384 and 357 person-hours of searching in 1992, 1993 and 1994, respectively. Nineteen nests found in hunter’s blinds or artificial structures (e.g., oil drums, small fenced plot within an electrical tower) were excluded from subsequent analyses. Combined nest densities for all islands were 1.3, 1.2 and 2.3 nests ha−1 during the 3 years of the study, respectively. Gadwall (Anas strepera L.), mallard (Anas platyrhynchos L.) and northern pintail (Anas acuta L.) were the most abundant species totaling nearly 75% of the duck nesting population every year (Table 2). Species composition did not vary among years 2 = 16.6, P = 0.08). (χ10
0.5 0.7 1.1
1.1 0.8 2.4
1.0 1.8 7.0
– – 2.3
– – 0.9
a DNC93 and DNC94 refer to the dense nesting cover treatments established in 1993 and 1994, respectively. b Nest density established before habitat improvements.
In 1994, the proportion of nests found in each treatment varied with nesting chronology (Table 3; 2 = 26.4, P = 0.003). The DNC93 system had a χ10 greater percentage of nests initiated early and at an intermediate date than later in the season. Ploughed field had also more early nesters (mallard and pintail), whereas DNC94 and unimproved pasture had more late nesters. Nest density in each treatment varied from 0.5 to 1.1 nests ha−1 in 1992, with improved pasture having the lowest density (Table 4). These densities, however, are underestimated because some nests (n = 34 or 0.3 nest ha−1 ) could not be associated to a treatment (loss of data). In 1993 and 1994, after fencing and DNC seeding, idle field and DNC93 had more nests per hectare than any other treatments. In 1992, the number of nests found in each treatment did not differ from the expected number based on the relative area covered by each treatment (Fig. 3; χ32 = 5.47, P = 0.15). In 1993, more nests than expected were found in idle field while fewer nests were found in improved and unimproved pastures (χ32 = 13.83, P < 0.0005). In 1994, idle field and
Table 3 Percentage of early, intermediate and late nests of ducks in six treatments on islands at Varennes, Quebec, 1994 Nesting chronologya
Treatment (number of nests) Idle field (111) Improved pasture (19) Unimproved pasture (37) DNC93b (35) DNC94b (35) Ploughed (14)
Early Intermediate Late
25 31 44
26 37 37
27 27 46
46 46 8
26 23 51
64 14 22
a Early: before 15 May; intermediate: between 16 May and 5 June; late: after 5 June. Nests with unknown initiation date were excluded from this analysis (n = 3). b DNC93 and DNC94 refer to the dense nesting cover treatments established in 1993 and 1994, respectively.
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Fig. 3. Observed and expected proportion of nests in six treatments on islands at Varennes, Quebec, 1992–1994. The expected numbers were based on the proportion of the area covered by each treatment. Significant differences (P < 0.05) are shown with asterisks.
DNC93 had also more nests than expected while improved pasture and ploughed field had fewer (χ52 = 81.2, P < 0.0005). 3.3. Nesting success and productivity Nesting success was overestimated in 1992 and 1993 because inadequate markers prevented fate determination of some nests that have probably been trampled by cattle. Nevertheless, 28/40 (70%) and 71/99 (72%) hatched at least one egg in 1992 and 1993, respectively. In 1994, the fate of 233/254 nests (92%) was determined: 76% of them hatched, 14% were depredated, 7% were abandoned and 3% were trampled. Mayfield nest success was 63% in 1994 (Table 5). Success was significantly lower in the improved pasture than in the other treatments except the ploughed
field. Lower success in the improved pasture was related to higher predation rate and trampling by cattle. Predation rate in the ploughed field was as high as in the improved pasture. Combining nest density and success indicates that the DNC93 was the most productive treatment with 5.7 hatched nests ha−1 followed by the idle field (1.9), the unimproved pasture (1.6), the DNC94 (1.2), the ploughed field (0.4) and the improved pasture (0.2). 3.4. Nesting in emergent vegetation In 1994, 16 nests were found in emergent vegetation in interior marshes, mostly between Grande-Ile and Ile-aux-Fermiers. These included eight nests of redhead (Aythya americana Eyton), six of mallard and two of unknown species. Twelve (75%) of the nests hatched at least one egg.
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Table 5 Mayfield nest success and fate of nests in six treatments on islands at Varennes, Quebec, 1994 Treatment
Idle field Improved pasture Unimproved pasture DNC93c DNC94c Ploughed Total
na
110, 105 21, 18 37, 34 35, 29 34, 32 15, 15 252, 233
Mayfield success (%)
69 15 68 82 53 47 63
ab
95% confidence intervals
58–81 5–46 51–89 67–100 35–81 21–99 55–71
b a a a ab
Fate (%) Hatched
Depredated
Abandoned
Trampled
81 39 76 86 72 73 76
12 28 6 10 16 27 14
7 0 18 4 12 0 7
0 33 0 0 0 0 3
a Numbers of nests used to calculate Mayfield success and fate of nests, respectively. Nests with unknown fate are excluded for calculations of apparent nest success (hatched). b Percentages followed by the same letter are not significantly different (P > 0.05). c DNC93 and DNC94 refer to the dense nesting cover treatments established in 1993 and 1994, respectively.
3.5. Costs of habitat improvements The improved pasture was the most expensive treatment because of the higher price of seeds and fencing (Table 6). Fencing was considered only for pastures assuming that cover was indirectly protected from grazing in DNC and idle field. When cows are present, costs associated with unimproved pasture should be added when establishing idle fields or DNC.
4. Discussion The study lacked spatial replication because it was impossible to find other islands similar in size, cover and distance from shore. Moreover financial Table 6 Cost per hectare (1997 $CDN) of habitat improvements on islands at Varennes, Quebec Treatment
Ground Chemical Seeds Fencingc Total a preparation productsb
Improved pasture 33 Unimproved pasture – Dense nesting cover 33
180 – 180
192d 474 – 474 135e –
879 474 348
a Includes land tillage ($14), spreading of herbicide ($2), harrowing ($9), seeding ($6) and spreading of fertilizers ($2). b Includes fertilizers ($94), lime ($76) and herbicide ($10). c Permanent fences for 1 ha (100 m × 100m) = 400 m. Cost includes labor and material. d Seeds: 20 kg ha−1 of a mixture of Bromus sp. (24%), Phleum pratense (34%), Melilotus officinalis (34%) and Trifolium sp. (8%). e Seeds: 16 kg ha−1 of a mixture of Phalaris arundinacea (56%) and Festuca elatior (44%).
constraints precluded the set up of a large scale replicated experiment. Nevertheless, temporal replication (before and after) was utilized to circumvent this problem. Furthermore, the study results are considered applicable to the Varennes islands and to other nearby islands of the St. Lawrence river. Results from this study, along with those of Barker et al. (1990), indicate that with appropriate management, use of prairies by cattle and their improvements for nesting waterfowl is possible. Even though the rotational grazing system and cover improvement did not result in a greater overall nest density in 1993, changes in nest distribution occurred and a greater proportion of nests were found in the idle field. Two years of rest was sufficient for the plants to recover and to establish new production. In 1994, there was more live and dead biomass in the idle field than in the improved pasture. The number of duck nests increased in the idle field and was higher than expected based on the area covered by this treatment whereas it was lower than expected in the improved pasture. Before the transfer of cattle in July, unimproved pasture had more vegetation than the improved pasture and this resulted in an increase of duck nest numbers in 1994. Restricting cattle to a smaller improved pasture was clearly beneficial for the overall waterfowl production on the islands. Seeding dense vegetation was an effective way of improving nesting cover on the St. Lawrence river islands. Newly sown DNC did not have enough litter in May to be suitable for early nesters. Two years after its establishment, however, the DNC93 had reached a density of 7.0 nests ha−1 with high nest success. This
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contrasts with results in southern Saskatchewan where only 1.1–1.4 nests ha−1 with 8–26% nest success were found in DNC plots (McKinnon and Duncan, 1999). In dryer regions such as the mid-continent prairies, DNC reaches maximum growth after 3–5 years and may become too dense for nesting when 7–8 years old (Duebbert and Kantrud, 1974; Duebbert et al., 1983). Maximum growth and a reduction in the value of DNC for nesting waterfowl could occur over a shorter time interval in Quebec where growing conditions are better. In this case, grazing by cattle during short periods as it was done in the fall 1993 on the Varennes islands, could be used as a tool to maintain cover quality of DNC. Nest densities on islands at Varennes were similar to those on other artificial or natural islands in southern Quebec (Bélanger and Tremblay, 1989; Bélanger and Lehoux, 1995) but lower than in the Prairie pothole region, reflecting different abundance of waterfowl (Giroux, 1981; Duebbert, 1982; Willms and Crawford, 1989). Gadwall, mallard, and northern pintail were the most abundant species nesting at Varennes consistent with the results reported by Bélanger and Lehoux (1995) for islands in southern Quebec. Gadwall and mallard are common island nesters but the use of islands by pintail is less frequent (Giroux, 1981; Duebbert et al., 1983). This may be attributed to regional variation in the abundance of this species and to the low and scarce vegetation found on some parts of islands of the St. Lawrence river, providing suitable nesting cover for pintails (Bélanger and Tremblay, 1989; Bélanger and Lehoux, 1995). About one third of the nests in the improved pasture were trampled. Cow density increases with reduction of area allocated to grazing and therefore the probability of nest trampling is higher (Jensen et al., 1990). Although the present study recorded a high percentage of nests destroyed by cattle, the total proportion of trampled nests for all the islands remained low (3%) after fencing. Trampling of nests by cattle seems to be of secondary importance compare to the effects of grazing since many studies have also showed a low percentage of trampled nests with specialized grazing systems (Koerth et al., 1983; Bareiss et al., 1986). High nest success is typical of island nesting ducks because isolation from mainland reduces mammalian predation (Lokemoen and Woodward, 1992). The absence of trees at Varennes may have also reduced
nest predation by raccoons and by birds like American crows (Corvus brachyrhyncos Brehm), which are more important predators when they have perches. Herring gull (Larus argentatus Pont.) and Great Black-backed Gull (Larus marinus L.) are also known to prey upon duck nests but their numbers were low. Before fencing, grazing and trampling of interior marshes by cattle was considerable and emergent vegetation was nearly absent. Excluding cattle from marsh edges allowed over-water nesting by mallard and redhead. This record of breeding redheads at Varennes is one of the most northeastern one for that species (Gauthier and Aubry, 1995). Emergent vegetation can provide additional space for pairs as well as good brood rearing habitat both as escape cover and support for invertebrates that serve as food for ducklings (Whyte et al., 1981). A larger number of broods was recorded in marshes on and around the islands after fencing (Bélanger, L., unpublished data). Brood survival may have also been better in 1993 than in 1992, contributing to the increase in the number of duck nests in 1994. Improved pasture was the most expensive management and resulted in low nest production but these expenditures were necessary to keep cattle in a more restricted area with good forage. The DNC system was expensive compared to idle fields but had three times as many successful nests per hectare than idle fields. Life expectancy of the seeded DNC is estimated to be more than 10 years (Lokemoen, 1984) with approximately $1000 per year for maintenance and rotation of cattle. Long-term effects of improvements were not evaluated and costs could be amortized over the years. Benefits may then be higher if duck numbers increase with homing of successful females (Lokemeon et al., 1990).
5. Conclusions Rotational grazing and cover improvement should be established on islands of the St. Lawrence river where grazing by cattle limits waterfowl production. Further research should be done, however, before large scale implementation of these habitat improvements could be done on the mainland in northeastern Canada where duck populations are lower than in the Prairie region. Reduction of cover by grazing has more consequences on the mainland because mammalian pre-
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dation is more important (Kirsh, 1969). Beneficial effects of cattle restriction could then be even greater. The DNC system, however, may be relatively less productive on the mainland in southern Quebec and other areas with less abundant waterfowl population because it seems to be more effective in reducing avian than mammalian predation (Clark and Nudds, 1991). Recent studies confirmed that prohibitively large areas of DNC would be required to have a substantial effect on regional duck population in southern Saskatchewan (McKinnon and Duncan, 1999). In integrated land management and sustainable development strategies, these habitat improvements could also be advantageous to landowners. Increase in beef production and reduction of soil erosion, two beneficial effects of specialized grazing systems, are strong arguments to persuade farmers to use rotational grazing systems to benefit both waterfowl and cattle (Barker et al., 1990; Kirby et al., 1992). Restricting access of cattle to some sectors of the islands during the fall season may also reduce potential conflicts with waterfowl hunters. Finally, the effects of these duck-oriented management practices on other prairie bird species should also be considered since cattle grazing can reduce the abundance of these species (Bélanger and Picard, 1999).
Acknowledgements We are thankful to C. Berthiaume, F. Blouin, A. Cossette, G. Couture, E. Desfossés, S. Goupil, J. Hamel, J. Lefebvre, C. Miqueu and F. St-Pierre for their assistance in the field and laboratory. We would also like to acknowledge the work of Ducks Unlimited staff for managing the islands. This study was financially supported by the Canadian Wildlife Service through the Eastern Habitat Joint Venture and the St. Lawrence Action Plan and by the Université du Québec à Montréal. We thank B. Pollard and two anonymous reviewers for their comments on the manuscript. References Anonymous, 1986. North American Waterfowl Management Plan. Canadian Wildlife Service, Environment Canada and U.S. Fish and Wildlife Service, Department of the Interior, 36pp.
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Bareiss, L.J., Schulz, P., Guthery, F.S., 1986. Effects of short-duration and continuous grazing on bobwhite and wild turkeys nesting. J. Range Manage. 39, 259–260. Barker, W.T., Sedivec, K.K., Messmer, T.A., Higgins, K.F., Hertel, D.R., 1990. Effects of specialized grazing systems on waterfowl production in south-central North Dakota. Trans. North Am. Wildl. Nat. Resour. Conf. 55, 462–474. Bélanger, L., Picard, M., 1999. Cattle grazing and avian communities of the spring flooded prairies of the St. Lawrence River islands. J. Range Manage. 52, 332–338. Bélanger, L., Lehoux, D., 1995. Use of various habitat types by nesting ducks on islands between Montreal and Trois-Rivieres. Can. Wildl. Serv. Occas. Pap. 87, 1–26. Bélanger, L., Tremblay, S., 1989. Ducks nesting on artificial islands in Quebec. Wildl. Soc. Bull. 17, 233–236. Bellrose, F.C., 1979. Species distribution, habitats, and characteristics of breeding dabbling ducks in North America. In: T. A. Bookhout (Ed.), Waterfowl and Wetlands — an Integrated Review. The Wildlife Society Madison, pp. 1–15. Bilanski, W.K., Ghate, S.R., 1978. Determining moisture content of alfalfa using a microwave oven. Ontario Ministry of Renewable Resources. Fact Sheet 40, 1–2. Clark, G.R., Nudds, D.T., 1991. Habitat patch size and duck nesting success: the crucial experiments have not been performed. Wildl. Soc. Bull. 19, 534–543. Conrad, H.R., Martz, F.A., 1985. Forages for dairy cattle. In: M.E. Heath, R.F. Barnes, D.S. Metcalfe (Eds.), Forages — The science of grassland agriculture, Iowa State University Press, Ames, Iowa, pp. 550–559. Duebbert, H.F., 1969. High nest density and hatching success of ducks on South Dakota Cap Land. Trans. N. Am. Wildl. Nat. Resour. Conf. 34, 218–229. Duebbert, H.F., 1982. Nesting of waterfowl on islands in Lake Audubon, North Dakota. Wildl. Soc. Bull. 10, 232–237. Duebbert, H.F., Lokemoen, J.T., Sharp, D.E., 1983. Concentrated nesting of mallards and gadwalls on Miller Lake Island, North Dakota. J. Wildl. Manage. 47, 729–740. Duebbert, H.F., Kantrud, H.A., 1974. Upland duck nesting related to land use and predator reduction. J. Wildl. Manage. 38, 257– 265. Francis, W.J., 1968. Temperature and humidity conditions in potential pheasant nesting habitat. J. Wildl. Manage. 33, 36–46. Gauthier, J., Aubry, Y., 1995. Les oiseaux nicheurs du Quebec: Atlas des oiseaux nicheurs du Quebec méridional. Association québécoise des groupes ornithologiques, la Société Quebecoise de protection des oiseaux and le Service Canadien de la Faune, Quebec, Environnement Canada, Montréal, 1295pp. Gilbert, D.W., Anderson, D.R., Ringelman, J.K., Szymczak, M.R., 1996. Response of nesting ducks to habitat management on the Monte Vista National Wildlife Refuge Colorado. Wildl. Monogr. 131, 1–44. Giroux, J.-F., 1981. Use of artificial islands by nesting waterfowl in southeastern Alberta. J. Wildl. Manage. 45, 669–679. Gjersing, F.M., 1975. Waterfowl production in relation to rest rotation grazing. J. Range Manage. 28, 37–42. Gloutney, M.L., Clark, R.G., Afton, A.D., Huff, G.J., 1993. Timing of nest searches for upland nesting waterfowl. J. Wildl. Manage. 57, 597–601.
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Jensen, H.P., Rollins, D., Gillen, R.L., 1990. Effects of cattle stock density on trampling loss of simulated ground nests. Wildl. Soc. Bull. 18, 71–74. Johnson, D.H., 1979. Estimating nest success: the Mayfield method and an alternative. Auk 96, 651–661. Kie, J.G., Bleich, V.C., Medina, A.L., Yoakum, J.D., Thomas, J.W., 1994. Managing rangelands for wildlife. In: Bookhout, T.A. (Ed.), Research and Management techniques for wildlife and habitats, The Wildlife Society, Bethesda, Md, pp. 663–688. Kirby, R.E., Ringelman, J.K., Anderson, D.R., Sojda, R.S., 1992. Grazing on National Wildlife Refuges: do the needs outweigh the problems? Trans. North Am. Wildl. Nat. Resour. Conf. 57, 611–626. Kirsh, L.M., 1969. Waterfowl production in relation to grazing. J. Wildl. Manage. 33, 821–828. Kirsh, L.M., Duebbert, H.F., Kruse, A.D., 1978. Grazing and haying effects on habitats of upland nesting birds. Trans. North Am. Wildl. Nat. Resour. Conf. 43, 486–497. Klett, A.T., Shaffer, T.L., Johnson, D.H., 1988. Duck nest success in the Prairie pothole region. J. Wildl. Manage. 52, 431–440. Koerth, B.H., Webb, W.M., Bryant, F.C., Guthery, F.S., 1983. Cattle trampling of simulated ground nests under short duration and continuous grazing. J. Range Manage. 36, 385–386. Krapu, G.L., Talent, L.G., Dwyer, T.J., 1979. Marsh nesting by mallards. Wildl. Soc. Bull. 7, 104–110. Kruse, A.D., Bowen, B.S., 1996. Effects of grazing and burning on densities and habitats of breeding ducks in North Dakota. J. Wildl. Manage. 60, 233–246. Livezey, B.C., 1981. Duck nesting in retired croplands at Horicon National Wildlife Refuge, Wisconsin. J. Wildl. Manage. 45, 27–37.
Lokemoen, J.T., 1984. Examining economic efficiency of management practices that enhance waterfowl production. Trans. North Am. Wildl. Nat. Resour. Conf. 47, 584–607. Lokemoen, J.T., Duebbert, H.F., Sharp, D.E., 1990. Homing and reproductive habits of mallards, gadwalls, and blue-winged teal. Wildl. Monogr. 106, 1–28. Lokemoen, J.T., Woodward, R.O., 1992. Nesting waterfowl and water birds on natural islands in the Dakotas and Montana. Wildl. Soc. Bull. 20, 163–171. McKinnon, D.T., Duncan, D.C., 1999. Effectiveness of dense nesting cover for increasing duck production in Saskatchewan. J. Wildl. Manage. 63, 382–389. Pasitschniak-Arts, M., Messier, F., 1995. Risk of predation on waterfowl nests in the Canadian prairies: effects of habitat edges and agricultural practices. Oikos 73, 347–355. Rearden, J.D., 1951. Identification of waterfowl nest predators. J. Wildl. Manage. 15, 386–395. Robel, R.J., Briggs, J.N., Dayton, A.D., Hulbert, I.C., 1970. Relationships between visual obstruction measurements and weight of grassland vegetation. J. Range Manage. 23, 295–297. Sugden, L.G., Beyersbergen, G.W., 1984. Farming intensity on waterfowl breeding grounds in Saskatchewan parklands. Wildl. Soc. Bull. 12, 22–26. Westerskov, K., 1950. Methods of determining the age of game birds eggs. J. Wildl. Manage. 14, 56–57. Whyte, R.J., Silvy, N.J., Cain, B.W., 1981. Effects of cattle on duck food plants in southern Texas. J. Wildl. Manage. 45, 512–515. Willms, M.A., Crawford, R.D., 1989. Use of earthen islands by nesting ducks in North Dakota. J. Wildl. Manage. 53, 411–417.
Benefits of rotational grazing and dense nesting cover for island-nesting waterfowl in southern Quebec Stéphane Lapointea,1 , Jean-François Giroux a,∗ , Luc Bélanger b , Bernard Filion c a
Département des sciences biologiques, Université du Québec à Montréal, C.P. 8888, Succursale Centre-ville, Montréal, Québec, Canada H3C 3P8 b Environment Canada, Canadian Wildlife Service, 1141 route de l’Église, C.P. 10100, Ste-Foy, Québec, Canada G1V 4H5 c Ducks Unlimited Canada, 710 rue Bouvier, suite 260, Québec, Canada G2J 1A7 Received 7 July 1998; received in revised form 9 August 1999; accepted 29 September 1999
Abstract Intensification of agricultural practices is an important factor responsible for the decline of duck populations throughout North America. More than 200 islands covering a total of 5000 ha are found in the St. Lawrence river between Montreal and Trois-Rivieres in southern Quebec. The value of these islands as duck nesting habitat, however, is often limited by cattle grazing. The effects of two types of habitat improvements, rotational grazing and establishment of dense nesting cover (DNC), on island-nesting waterfowl was studied from 1992 to 1994. Four treatments were compared: idle fields with no vegetation improvement but exclusion of cattle, improved pastures with seeding of forage plants for cattle, DNC fields with improved cover for ducks and exclusion of cattle and unimproved pastures used after the duck nesting season. Before habitat improvements, grazing by cattle reduced dry mass of green vegetation by 53% relative to ungrazed plots. No difference was found in the biomass of live (green) and dead (residual) vegetation among the islands’ sections before treatments. Nest density and the number of expected nests based on the area covered by each habitat were also similar among sections before treatment. Gadwall (Anas strepera L.), mallard (Anas platyrhynchos L.), and pintail (Anas acuta L.) were the most abundant species nesting on the islands and this was not affected by treatments. Two years after habitat improvements, the number of duck nests increased. Idle fields and 2-year old DNC had greater visual obstruction, more residual vegetation and more litter. Densities of 2.8 and 7.0 nests ha−1 with 69 and 82% Mayfield nest success were recorded in the idle and DNC fields, respectively. Nest success was low in improved pasture where a large proportion of nests were trampled (33%) or depredated (28%). Fencing permitted growth of emergent vegetation which enabled over-water nesting by ducks. These results indicate that with appropriate management, coexistence of cattle and nesting waterfowl is possible on islands of the St. Lawrence river. ©2000 Elsevier Science B.V. All rights reserved. Keywords: Ducks; Nesting density; Nesting success; Rotational grazing; DNC; Quebec
1. Introduction ∗ Corresponding author. Tel.: +1-514-987-3000 (ext. 3353); fax: +1-514-987-4647. E-mail address: [email protected] (J.-F. Giroux). 1 Present address: Pharmascience inc, 6111 Royalmount Avenue, suite 100, Montr´eal, Qu´ebec, Canada H4P 2T4.
Expansion of farming and changes to more intensive agricultural practices are among the most important factors responsible for the decline of duck populations throughout North America (Sugden and Beyersber-
0167-8809/00/$ – see front matter ©2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 8 8 0 9 ( 9 9 ) 0 0 1 3 2 - 2
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gen, 1984). Ducks now have to nest in the remaining small and fragmented habitats where predation is often higher than in contiguous habitats (Clark and Nudds, 1991; Pasitschniak-Arts and Messier, 1995). Even though dabbling duck populations have less declined in eastern than in western North America, biologists are concerned with the rate at which wetlands and their surroundings are being converted into farmlands and industrial lands (Anonymous, 1986). They are therefore seeking ways to overcome loss of natural habitats. Island construction is one of the most productive techniques because ducks can nest at higher densities and with better success attributed to lower mammalian predation (Giroux, 1981; Duebbert, 1982). However, island construction is expensive and could be inappropriate where duck populations are low (Lokemoen, 1984; Bélanger and Tremblay, 1989). Managing existing islands may therefore be a more cost-efficient strategy (Lokemoen and Woodward, 1992). In Quebec, the most productive areas for nesting dabbling ducks are located on islands of the St. Lawrence river. More than 200 islands ranging in size from <0.1 to >2000 ha and representing nearly 5000 ha of land are found between Montreal and Trois-Rivieres. However, the value of these islands for ground-nesting birds is often limited by cattle grazing (Bélanger and Lehoux, 1995; Bélanger and Picard, 1999). This reduces the screening effect of vegetative cover, which can lower nest density and success (Lokemoen et al., 1990; Gilbert et al., 1996; Kruse and Bowen, 1996). Grazing can also affect residual vegetation, an important component of nesting cover for early nesting ducks (Duebbert, 1969; Kirsh, 1969; Kirsh et al., 1978). It may provide ideal temperature and humidity for better egg hatchability (Francis, 1968; Duebbert, 1969). In addition, grazing and trampling of shoreline vegetation decrease over-water nesting (Krapu et al., 1979; Kirby et al., 1992). Finally, trampling of eggs by cattle directly affects nest success (Jensen et al., 1990). Studies have shown that it is possible to reduce the adverse effects of cattle with rotational grazing systems (Gjersing, 1975; Barker et al., 1990). Pastures are divided into smaller range units and cattle are periodically moved among these units (Kie et al., 1994). Rotation of cattle throughout the growing season maintains plants at a vegetative stage that provides the most digestible forage (Conrad and Martz,
1985). Thus, higher stocking rates are possible and calf weight gain per hectare is better than with continuous grazing (Barker et al., 1990). Furthermore, this leaves more undisturbed cover for nesting waterfowl because less area is required for cattle. The establishment of dense nesting cover (DNC) has also been proposed to enhance duck productivity because it generally supports higher nest densities and success (Duebbert and Kantrud, 1974; Klett et al., 1988; but see McKinnon and Duncan, 1999 for different results). Improved nesting cover is easy and less expensive to establish and can be sown on islands where cover is inadequate (Lokemoen, 1984; Willms and Crawford, 1989). Several years, however, may be needed before cover becomes adequate for nesting (Livezey, 1981). The effectiveness of rotational grazing systems and cover improvements on nesting waterfowl has been generally demonstrated in the mid continent of North America. This area is characterized by productive wetlands called prairie potholes that support large numbers of breeding ducks (Bellrose, 1979). On the other hand, little is known about the effects of these techniques in eastern North America where wetlands are often located along rivers or coastal shores and where breeding populations of ducks are less numerous than in the mid continent. Moreover, growing conditions are different between the dryer prairie region and eastern North America and this could affect the establishment of seeded vegetation. The objective of this study was therefore to evaluate the effectiveness of rotational grazing systems and cover improvements to enhance nesting habitat for waterfowl in eastern North America. More specifically, the aims were to compare different grassland management practices on (1) quality of nesting cover, (2) nest density of dabbling ducks and (3) their nesting success on islands of the St. Lawrence river in southern Quebec.
2. Material and methods 2.1. Study area The study was conducted between 1992 and 1994 on four adjacent islands near Varennes, Quebec, Canada (45◦ 400 N, 73◦ 270 W), 16 km northeast of Montreal along the St. Lawrence river. The climate is
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continental temperate, with a mean annual temperature of 6.1◦ C and a total annual rainfall of 768 mm. The islands ranged in size between 9.4 and 59.8 ha for a total of 111.5 ha. No trees or shrubs were present. As water levels recede following spring run-off, the islands are joined together forming small interior marshes with stands of cattail (Typha angustifolia L.), big burreed (Sparganium eurycarpum Engelm) and arrowhead (Sagittaria spp.). Cattle were brought to the islands by boat in late May to early June and removed in November. A total of 114, 100 and 85 cows were present in 1992, 1993 and 1994, respectively. During the first year, cattle grazed everywhere on the islands (Fig. 1).
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Ile-aux-Fermiers, Masta and St. Patrice islands were dominated by red-top (Agrostis alba L.), red fescue-grass (Festuca rubra L.), Kentucky bluegrass (Poa pratensis L.) and cow vetch (Vicia cracca L.). Grande-Ile was covered with reed canary grass (Phalaris arundinacea L.) and Canada reed-grass (Calamagrostis canadensis [Michx.] Beauv.). In August 1992, Ducks Unlimited Canada seeded DNC, improved the quality and quantity of forage of some pastures and set up a series of electric fences to establish a rotational grazing system. The forage on Grande-Ile was improved by sowing 19.2 ha of timothy (Phleum pratense L.), sweet clover (Melilotus officinalis [L.] Desr.), smooth brome (Bromus
Fig. 1. Location of the treatments on islands at Varennes, Quebec, 1992–1994.
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inermis Leyss.) and clover (Trifolium spp.). Mixtures of reed canary grass in association with timothy, tall fescue-grass (Festuca elatior L.), Orchard grass (Dactylis glomerata L.) or tall wheat grass (Agropyron elongatum [Host] Beauv.) were sown on 5 ha on Grande-Ile to establish the DNC. Non-selective herbicide (glyphosate) was applied to treated fields before cultivation. Masta, St. Patrice as well as parts of Grande-Ile and Ile-aux-Fermiers were left idle with no grazing. Interior marshes were also protected from cattle by permanent or temporary fences. In 1993, a rotational grazing system was established (Fig. 1). From the end of May to mid July, cattle were restricted to the improved pasture. After the duck nesting season, they were moved to the unimproved pasture on Ile-aux-Fermiers until mid September. Another rotation between these two pastures took place between mid September and the end of October. Finally, cattle were allowed to graze freely on all islands (including in DNC) for 2 weeks until they were removed in mid November. During the duck nesting period from May to July, there were four treatments: idle field (59.9 ha), improved pasture with cattle (19.2 ha), unimproved pasture without cattle (27.4 ha) and a 1-year old DNC (DNC93: 5.0 ha). In the fall of 1993, another 9.4 and 5.6 ha of DNC were established on St. Patrice and Grande-Ile, respectively, by sowing Western wheat grass (Agropyron smithii Rydb.) and crested wheat grass (Agropyron cristatum[L.] Gaertn.). A portion of Ile-aux-Fermiers was ploughed so it could be converted to improved pasture but was not seeded on time. This pasture was therefore a ploughed field (17.6 ha) during the 1994 duck nesting season. The other treatments included: idle field (39.1 ha), improved pasture with cattle (19.2 ha), unimproved pasture without cattle (15.6 ha), a 1-year old DNC (DNC94: 15.0 ha) and a 2-year old DNC (DNC93: 5.0 ha). Rotation of cattle among pastures in 1994 was similar to the previous year.
2.2. Cover evaluation In 1992, the effect of cattle grazing on the vegetation was evaluated by establishing 50 0.5 m × 1.0 m exclosures that were randomly located on the four islands and put in place before the arrival of cattle. In July, all the vegetation above 1 cm was clipped in a
10 cm × 10 cm randomly selected quadrat within each exclosure and in grazed sites, also located randomly at more than 50 m away from the exclosures. Vegetation was sorted into live biomass defined as any green plants or plant parts, and residual vegetation that consisted of dead biomass from the previous and current years. Vegetation was then dried to constant weight in a micro-wave oven (Bilanski and Ghate, 1978) and weighed to the nearest 0.1 g. Data from unfenced plots were also used to compare live and dead biomass of vegetation among treatments before and after the management. In 1993, the same 50 plots were used while in 1994 an additional 39 plots were randomly located, for a total of 89. Sampling was conducted during the first week of July each year, using the same procedure. In 1994, visual obstruction readings were taken every 10 m along a 100 m NE–SW line in each plot using a Robel et al. (1970) pole. Readings were taken at a distance of 4 m from a height of 1 m. These readings give an index of cover quality by taking into account height and density of vegetation; it is highly corelated to biomass (Robel et al., 1970). Depth of residual vegetation accumulated on the ground was measured at the same time with a ruler (±0.5 cm). Visual obstruction and litter depth readings were taken every 2 weeks from early May to mid July.
2.3. Nest search Nest searches were conducted three times each year at 3-week intervals starting at the end of May. All upland habitats on the islands were searched for waterfowl nests. In 1994, newly established patches of emergent vegetation were also searched for nests by walking through the vegetation. Searches were done between 06:00 and 12:00 hours when most females are attending their nests (Gloutney et al., 1993). Four to eight observers walked side-by-side along transects, making noise and beating vegetation with 2.5 m bamboo sticks in order to flush nesting females. We consider that nest detection probability was equivalent among treatments characterized by herbaceous cover without shrubs. Species was determined by identifying the flushing female or using egg and down characteristics. Nest location was marked with 1 m long bamboo sticks in 1992 and 1993, and with reed-grass (Phragmites communis Trin.) stalks in 1994. Markers were
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placed 4 m NE of the nest. Semi-rigid plastic poles were used as nest markers in pastures in 1993 and 1994 because bamboo sticks proved to be inadequate markers when cattle were present (most of them fell in 1992). Nest locations were also marked on 1 : 10 000 aerial color photographs. A nest was defined as a bowl containing at least one egg. Number of eggs, amount of down and incubation stage evaluated by floatation (Westerskov, 1950) were recorded at each visit. Nests were revisited during the following nest search or after the expected hatching date. A nest was considered successful if at least one egg hatched. Unsuccessful nests were recorded as depredated if there was evidence of broken or missing eggs, abandoned if the nest was not tended by a female and had cold eggs, and trampled if the clutch and the surrounding area were destroyed by cattle hooves. Predators were identified when possible following the criteria of Rearden (1951) based on remaining eggshells and/or characteristics of the nests. 2.4. Costs of habitat improvements For each treatment, costs of ground preparation (tillage, harrowing, seeding and spreading of herbicides and fertilizers), chemical products, seeds and fencing were evaluated. Costs for ground preparation were obtained from Le Comité des références économiques en agriculture du Québec (1994) and do not represent the actual costs involved during the study because some operations were done on an experimental basis and were therefore more costly than regular operations. Seed prices are from Labon. All prices are in 1997 CDN dollars. 2.5. Data analyses Paired t-tests were used to evaluate the effect of cattle grazing by comparing biomass between ungrazed and grazed plots. Comparisons among treatments or sampling periods for live and dead biomass, visual obstruction and litter depth were made using analyses of variance (ANOVAs). Homogeneity of variances and normality were verified and logarithmic transformations were applied when necessary. When a significant effect was found, Tukey multiple comparison tests were performed to determine where differences occurred.
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Annual differences in the species composition of the breeding population were compared with χ 2 tests as well as the proportion of early, intermediate and late nests in each treatment. Comparisons of expected and observed distributions of nests among treatments were made using χ 2 . The proportion of the nesting population (expected numbers of nests) in each treatment was weighed proportional to the area covered by each habitat. For each year, contrast tests were used to determine where differences occurred among treatments. In 1994, nest success was calculated for each treatment using the Mayfield-40% method followed by pairwise comparisons of daily survival rates among treatments (Johnson, 1979). For all analyses, significance level was fixed at P = 0.05 and all means are shown ±1 SE. 3. Results 3.1. Nesting cover In July 1992, before any habitat improvements, grazing by cattle reduced live biomass by 53% (ungrazed plots: 671 ± 50 g m−2 ; grazed plots: 355 ± 37 g m−2 ; t47 = 5.88, P < 0.0001). However, there was more dead biomass (residual vegetation) in grazed than in ungrazed plots (122 ± 81 versus 81 ± 68 g m−2 ; t47 = 3.1, P = 0.004). In terms of cover quality, no difference among treatments was recorded for live (F3,46 = 2.08, P = 0.12) and dead biomass (F3,46 = 0.65, P = 0.59) in 1992 before the management (Table 1). In 1993, after fencing and DNC seeding, there was significantly more live biomass in DNC93 than in improved pasture (F3,46 = 3.38, P = 0.03). In 1994, DNC93 had more live biomass than all other treatments (F5,78 = 5.77, P < 0.0001). Finally, DNC93 and idle field also had more residual vegetation than improved pasture, DNC94 and ploughed field (F5,78 = 11.85, P < 0.0001). From May to July, the visual obstruction index increased in every treatment during the summer of 1994, except in improved pastures where it decreased after the arrival of cattle (Fig. 2; idle: F5,96 = 48.9; improved pastures: F5,138 = 46.8; unimproved pastures: F5,54 = 10.1; DNC93 fields: F5,24 = 11.3; DNC94 fields: F5,71 = 19.9; ploughed fields: F5,108 = 16.9,
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Table 1 Live and dead aboveground biomass (g m−2 dry mass) of vegetation used as nesting cover by ducks measured in July in six treatments on islands at Varennes, Quebec, 1992–1994 Treatment
na
1992b
1993
Live Idle field Improved pasture Unimproved pasture DNC93d DNC94d Ploughed
23, 23, 17 12, 12, 24 11, 10, 10 4, 5, 5 –, –, 13 –, –, 19
Dead
433 ± 60 212 ± 53 a 396 ± 90 a 369 ± 105 a – – ac
126 ± 14 130 ± 21 119 ± 37 77 ± 13 – –
a a a a
1994
Live
Dead
Live
Dead
577 ± 85 ab 419 ± 127 b 808 ± 155 ab 830 ± 198 a – –
86 ± 18 a 134 ± 51 a 207 ± 69 a 132 ± 96 a – –
780 ± 135 b 366 ± 71 b 632 ± 70 b 1631 ± 700 a 614 ± 130 b 327 ± 94 b
217 ± 40 a 50 ± 12 b 103 ± 24 ab 222 ± 82 a 24 ± 9 b 14 ± 6 b
a
Number of plots sampled in 1992, 1993 and 1994, respectively. Vegetation was sampled before establishment of treatments. c Means (±1 SE) followed by the same letters within a column are not significantly different (P > 0.05). d DNC93 and DNC94 refer to the dense nesting cover treatments established in 1993 and 1994, respectively. b
P < 0.0001, for all tests). Idle field and DNC93 had higher visual obstruction than improved pasture in early May (F5,82 = 20.79, P < 0.0001) and the difference remained significant between DNC93 and improved pasture throughout the summer (P < 0.0001).
Litter depth decreased during the summer but differences were only significant in idle fields (F5,96 = 3.38, P = 0.007), improved pastures (F5,138 = 27.3, P < 0.0001) and ploughed fields (F5,108 = 2.35, P = 0.05). Idle fields and DNC93 had more litter than improved
Fig. 2. Visual obstruction index measured with the Robel et al. (1970) pole and litter depth in six treatments during the summer 1994 on islands at Varennes, Quebec. Significant differences among treatments for each period are indicated by different letters (P < 0.05).
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Table 2 Species composition (%) of duck nests initiated on the islands at Varennes, Quebec, 1992–1994
Table 4 Number of duck nests per hectare in six treatments on islands at Varennes, Quebec, 1992–1994
Species
Year
Gadwall Mallard Pintail Shoveler American Wigeon Othersa
Year (number of nests) 1992 (139)
1993 (137)
1994 (254)
24 25 24 10 10 6
28 20 27 9 7 9
32 26 18 14 8 2
Treatment Idle Improved Unimproved DNC93a DNC94a Ploughed field pasture pasture
1992b 1.0 1993 1.5 1994 2.8
a Included American black duck (Anas rubripes Brewster), blue-winged teal (Anas discors L.), redhead (Aythya americana) and unidentified species.
pastures throughout the summer (P < 0.0001) while DNC94 and the ploughed fields had a very thin litter (Fig. 2). 3.2. Number of nests and species composition A total of 143, 143 and 263 duck nests were found in the upland portions of the islands during the 300, 384 and 357 person-hours of searching in 1992, 1993 and 1994, respectively. Nineteen nests found in hunter’s blinds or artificial structures (e.g., oil drums, small fenced plot within an electrical tower) were excluded from subsequent analyses. Combined nest densities for all islands were 1.3, 1.2 and 2.3 nests ha−1 during the 3 years of the study, respectively. Gadwall (Anas strepera L.), mallard (Anas platyrhynchos L.) and northern pintail (Anas acuta L.) were the most abundant species totaling nearly 75% of the duck nesting population every year (Table 2). Species composition did not vary among years 2 = 16.6, P = 0.08). (χ10
0.5 0.7 1.1
1.1 0.8 2.4
1.0 1.8 7.0
– – 2.3
– – 0.9
a DNC93 and DNC94 refer to the dense nesting cover treatments established in 1993 and 1994, respectively. b Nest density established before habitat improvements.
In 1994, the proportion of nests found in each treatment varied with nesting chronology (Table 3; 2 = 26.4, P = 0.003). The DNC93 system had a χ10 greater percentage of nests initiated early and at an intermediate date than later in the season. Ploughed field had also more early nesters (mallard and pintail), whereas DNC94 and unimproved pasture had more late nesters. Nest density in each treatment varied from 0.5 to 1.1 nests ha−1 in 1992, with improved pasture having the lowest density (Table 4). These densities, however, are underestimated because some nests (n = 34 or 0.3 nest ha−1 ) could not be associated to a treatment (loss of data). In 1993 and 1994, after fencing and DNC seeding, idle field and DNC93 had more nests per hectare than any other treatments. In 1992, the number of nests found in each treatment did not differ from the expected number based on the relative area covered by each treatment (Fig. 3; χ32 = 5.47, P = 0.15). In 1993, more nests than expected were found in idle field while fewer nests were found in improved and unimproved pastures (χ32 = 13.83, P < 0.0005). In 1994, idle field and
Table 3 Percentage of early, intermediate and late nests of ducks in six treatments on islands at Varennes, Quebec, 1994 Nesting chronologya
Treatment (number of nests) Idle field (111) Improved pasture (19) Unimproved pasture (37) DNC93b (35) DNC94b (35) Ploughed (14)
Early Intermediate Late
25 31 44
26 37 37
27 27 46
46 46 8
26 23 51
64 14 22
a Early: before 15 May; intermediate: between 16 May and 5 June; late: after 5 June. Nests with unknown initiation date were excluded from this analysis (n = 3). b DNC93 and DNC94 refer to the dense nesting cover treatments established in 1993 and 1994, respectively.
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Fig. 3. Observed and expected proportion of nests in six treatments on islands at Varennes, Quebec, 1992–1994. The expected numbers were based on the proportion of the area covered by each treatment. Significant differences (P < 0.05) are shown with asterisks.
DNC93 had also more nests than expected while improved pasture and ploughed field had fewer (χ52 = 81.2, P < 0.0005). 3.3. Nesting success and productivity Nesting success was overestimated in 1992 and 1993 because inadequate markers prevented fate determination of some nests that have probably been trampled by cattle. Nevertheless, 28/40 (70%) and 71/99 (72%) hatched at least one egg in 1992 and 1993, respectively. In 1994, the fate of 233/254 nests (92%) was determined: 76% of them hatched, 14% were depredated, 7% were abandoned and 3% were trampled. Mayfield nest success was 63% in 1994 (Table 5). Success was significantly lower in the improved pasture than in the other treatments except the ploughed
field. Lower success in the improved pasture was related to higher predation rate and trampling by cattle. Predation rate in the ploughed field was as high as in the improved pasture. Combining nest density and success indicates that the DNC93 was the most productive treatment with 5.7 hatched nests ha−1 followed by the idle field (1.9), the unimproved pasture (1.6), the DNC94 (1.2), the ploughed field (0.4) and the improved pasture (0.2). 3.4. Nesting in emergent vegetation In 1994, 16 nests were found in emergent vegetation in interior marshes, mostly between Grande-Ile and Ile-aux-Fermiers. These included eight nests of redhead (Aythya americana Eyton), six of mallard and two of unknown species. Twelve (75%) of the nests hatched at least one egg.
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Table 5 Mayfield nest success and fate of nests in six treatments on islands at Varennes, Quebec, 1994 Treatment
Idle field Improved pasture Unimproved pasture DNC93c DNC94c Ploughed Total
na
110, 105 21, 18 37, 34 35, 29 34, 32 15, 15 252, 233
Mayfield success (%)
69 15 68 82 53 47 63
ab
95% confidence intervals
58–81 5–46 51–89 67–100 35–81 21–99 55–71
b a a a ab
Fate (%) Hatched
Depredated
Abandoned
Trampled
81 39 76 86 72 73 76
12 28 6 10 16 27 14
7 0 18 4 12 0 7
0 33 0 0 0 0 3
a Numbers of nests used to calculate Mayfield success and fate of nests, respectively. Nests with unknown fate are excluded for calculations of apparent nest success (hatched). b Percentages followed by the same letter are not significantly different (P > 0.05). c DNC93 and DNC94 refer to the dense nesting cover treatments established in 1993 and 1994, respectively.
3.5. Costs of habitat improvements The improved pasture was the most expensive treatment because of the higher price of seeds and fencing (Table 6). Fencing was considered only for pastures assuming that cover was indirectly protected from grazing in DNC and idle field. When cows are present, costs associated with unimproved pasture should be added when establishing idle fields or DNC.
4. Discussion The study lacked spatial replication because it was impossible to find other islands similar in size, cover and distance from shore. Moreover financial Table 6 Cost per hectare (1997 $CDN) of habitat improvements on islands at Varennes, Quebec Treatment
Ground Chemical Seeds Fencingc Total a preparation productsb
Improved pasture 33 Unimproved pasture – Dense nesting cover 33
180 – 180
192d 474 – 474 135e –
879 474 348
a Includes land tillage ($14), spreading of herbicide ($2), harrowing ($9), seeding ($6) and spreading of fertilizers ($2). b Includes fertilizers ($94), lime ($76) and herbicide ($10). c Permanent fences for 1 ha (100 m × 100m) = 400 m. Cost includes labor and material. d Seeds: 20 kg ha−1 of a mixture of Bromus sp. (24%), Phleum pratense (34%), Melilotus officinalis (34%) and Trifolium sp. (8%). e Seeds: 16 kg ha−1 of a mixture of Phalaris arundinacea (56%) and Festuca elatior (44%).
constraints precluded the set up of a large scale replicated experiment. Nevertheless, temporal replication (before and after) was utilized to circumvent this problem. Furthermore, the study results are considered applicable to the Varennes islands and to other nearby islands of the St. Lawrence river. Results from this study, along with those of Barker et al. (1990), indicate that with appropriate management, use of prairies by cattle and their improvements for nesting waterfowl is possible. Even though the rotational grazing system and cover improvement did not result in a greater overall nest density in 1993, changes in nest distribution occurred and a greater proportion of nests were found in the idle field. Two years of rest was sufficient for the plants to recover and to establish new production. In 1994, there was more live and dead biomass in the idle field than in the improved pasture. The number of duck nests increased in the idle field and was higher than expected based on the area covered by this treatment whereas it was lower than expected in the improved pasture. Before the transfer of cattle in July, unimproved pasture had more vegetation than the improved pasture and this resulted in an increase of duck nest numbers in 1994. Restricting cattle to a smaller improved pasture was clearly beneficial for the overall waterfowl production on the islands. Seeding dense vegetation was an effective way of improving nesting cover on the St. Lawrence river islands. Newly sown DNC did not have enough litter in May to be suitable for early nesters. Two years after its establishment, however, the DNC93 had reached a density of 7.0 nests ha−1 with high nest success. This
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contrasts with results in southern Saskatchewan where only 1.1–1.4 nests ha−1 with 8–26% nest success were found in DNC plots (McKinnon and Duncan, 1999). In dryer regions such as the mid-continent prairies, DNC reaches maximum growth after 3–5 years and may become too dense for nesting when 7–8 years old (Duebbert and Kantrud, 1974; Duebbert et al., 1983). Maximum growth and a reduction in the value of DNC for nesting waterfowl could occur over a shorter time interval in Quebec where growing conditions are better. In this case, grazing by cattle during short periods as it was done in the fall 1993 on the Varennes islands, could be used as a tool to maintain cover quality of DNC. Nest densities on islands at Varennes were similar to those on other artificial or natural islands in southern Quebec (Bélanger and Tremblay, 1989; Bélanger and Lehoux, 1995) but lower than in the Prairie pothole region, reflecting different abundance of waterfowl (Giroux, 1981; Duebbert, 1982; Willms and Crawford, 1989). Gadwall, mallard, and northern pintail were the most abundant species nesting at Varennes consistent with the results reported by Bélanger and Lehoux (1995) for islands in southern Quebec. Gadwall and mallard are common island nesters but the use of islands by pintail is less frequent (Giroux, 1981; Duebbert et al., 1983). This may be attributed to regional variation in the abundance of this species and to the low and scarce vegetation found on some parts of islands of the St. Lawrence river, providing suitable nesting cover for pintails (Bélanger and Tremblay, 1989; Bélanger and Lehoux, 1995). About one third of the nests in the improved pasture were trampled. Cow density increases with reduction of area allocated to grazing and therefore the probability of nest trampling is higher (Jensen et al., 1990). Although the present study recorded a high percentage of nests destroyed by cattle, the total proportion of trampled nests for all the islands remained low (3%) after fencing. Trampling of nests by cattle seems to be of secondary importance compare to the effects of grazing since many studies have also showed a low percentage of trampled nests with specialized grazing systems (Koerth et al., 1983; Bareiss et al., 1986). High nest success is typical of island nesting ducks because isolation from mainland reduces mammalian predation (Lokemoen and Woodward, 1992). The absence of trees at Varennes may have also reduced
nest predation by raccoons and by birds like American crows (Corvus brachyrhyncos Brehm), which are more important predators when they have perches. Herring gull (Larus argentatus Pont.) and Great Black-backed Gull (Larus marinus L.) are also known to prey upon duck nests but their numbers were low. Before fencing, grazing and trampling of interior marshes by cattle was considerable and emergent vegetation was nearly absent. Excluding cattle from marsh edges allowed over-water nesting by mallard and redhead. This record of breeding redheads at Varennes is one of the most northeastern one for that species (Gauthier and Aubry, 1995). Emergent vegetation can provide additional space for pairs as well as good brood rearing habitat both as escape cover and support for invertebrates that serve as food for ducklings (Whyte et al., 1981). A larger number of broods was recorded in marshes on and around the islands after fencing (Bélanger, L., unpublished data). Brood survival may have also been better in 1993 than in 1992, contributing to the increase in the number of duck nests in 1994. Improved pasture was the most expensive management and resulted in low nest production but these expenditures were necessary to keep cattle in a more restricted area with good forage. The DNC system was expensive compared to idle fields but had three times as many successful nests per hectare than idle fields. Life expectancy of the seeded DNC is estimated to be more than 10 years (Lokemoen, 1984) with approximately $1000 per year for maintenance and rotation of cattle. Long-term effects of improvements were not evaluated and costs could be amortized over the years. Benefits may then be higher if duck numbers increase with homing of successful females (Lokemeon et al., 1990).
5. Conclusions Rotational grazing and cover improvement should be established on islands of the St. Lawrence river where grazing by cattle limits waterfowl production. Further research should be done, however, before large scale implementation of these habitat improvements could be done on the mainland in northeastern Canada where duck populations are lower than in the Prairie region. Reduction of cover by grazing has more consequences on the mainland because mammalian pre-
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dation is more important (Kirsh, 1969). Beneficial effects of cattle restriction could then be even greater. The DNC system, however, may be relatively less productive on the mainland in southern Quebec and other areas with less abundant waterfowl population because it seems to be more effective in reducing avian than mammalian predation (Clark and Nudds, 1991). Recent studies confirmed that prohibitively large areas of DNC would be required to have a substantial effect on regional duck population in southern Saskatchewan (McKinnon and Duncan, 1999). In integrated land management and sustainable development strategies, these habitat improvements could also be advantageous to landowners. Increase in beef production and reduction of soil erosion, two beneficial effects of specialized grazing systems, are strong arguments to persuade farmers to use rotational grazing systems to benefit both waterfowl and cattle (Barker et al., 1990; Kirby et al., 1992). Restricting access of cattle to some sectors of the islands during the fall season may also reduce potential conflicts with waterfowl hunters. Finally, the effects of these duck-oriented management practices on other prairie bird species should also be considered since cattle grazing can reduce the abundance of these species (Bélanger and Picard, 1999).
Acknowledgements We are thankful to C. Berthiaume, F. Blouin, A. Cossette, G. Couture, E. Desfossés, S. Goupil, J. Hamel, J. Lefebvre, C. Miqueu and F. St-Pierre for their assistance in the field and laboratory. We would also like to acknowledge the work of Ducks Unlimited staff for managing the islands. This study was financially supported by the Canadian Wildlife Service through the Eastern Habitat Joint Venture and the St. Lawrence Action Plan and by the Université du Québec à Montréal. We thank B. Pollard and two anonymous reviewers for their comments on the manuscript. References Anonymous, 1986. North American Waterfowl Management Plan. Canadian Wildlife Service, Environment Canada and U.S. Fish and Wildlife Service, Department of the Interior, 36pp.
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