Roost selection by the long-tailed bat, Chalinolobus tuberculatus, in temperate New Zealand rainforest and its implications for the conservation of bats in managed forests

BIOLOGICAL CONSERVATION

Biological Conservation 88 (1999) 261±276

Roost selection by the long-tailed bat, Chalinolobus tuberculatus, in temperate New Zealand rainforest and its implications for the conservation of bats in managed forests Jane A. Sedgeley a, b,*, Colin F.J. O'Donnell a, b a Department of Zoology, University of Otago, PO Box 56, Dunedin, New Zealand Science & Research Unit, Department of Conservation, Private Bag, Christchurch, New Zealand

b

Received 2 November 1997; received in revised form 27 May 1998; accepted 3 June 1998

Abstract Roost selection by the threatened New Zealand long-tailed bat (Chalinolobus tuberculatus) was examined in temperate beech (Nothofagus) rainforest in New Zealand. Seventy-three bats were radio-tracked during the summers of 1993±1997 to 304 roost cavities in 291 di€erent trees. Roost tree and site characteristics were compared with those of 593 randomly selected trees. Bats selected roosts on the basis of topography, forest composition and tree characteristics. Ninety-®ve percent of roost trees were in mature, open-structured lowland forest on the relatively ¯at valley ¯oor within 500 m of the forest edge. Four tree species (including dead trees) were used as day roosts. C. tuberculatus did not discriminate between tree species per se, but selected roost trees on the basis of functional characteristics associated with these trees. Bats actively selected taller trees which had relatively low canopy closure, larger stem diameters, larger trunk surface areas and greater numbers of cavities than random trees. Red beech (Nothofagus fusca) and dead trees were most likely to provide these preferred characteristics. Seventy-four percent of roost trees were c. 100± >600 years of age. Such trees are targeted for removal under most forest management practices. Selection of specialised roosts, high roost lability and low levels of roost re-use indicate that C. tuberculatus need large areas of mature forest. We predict that outside protected areas, the low availability of suitable roost trees may limit bat populations. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Bats; Chalinolobus; Tree-roosts; Roost-selection; Logging

1. Introduction Many insectivorous bats spend over half of each day in their roosts (Vaughan and O'Shea, 1976), and for temperate zone bats this may extend to months at a time as they hibernate (Ransome, 1990). Bats utilise a wide range of structures as roosts, including caves, rock crevices, tree cavities, foliage and man-made structures (reviewed in Kunz, 1982). Roosts can provide protection from weather and predators (Vaughan and O'Shea, 1976; Vaughan, 1987), a relatively stable micro-climate (Herreid II, 1963; Burnett and August, 1981), a focus for social interactions (Morrison, 1980; Wilkinson, 1985; Daniel, 1990) and a place in which to mate and rear young (Kunz, 1982).

* Corresponding author at Science & Research Unit, Department of Conservation, Private Bag, Christchurch, New Zealand. Tel.: +643-379-9758; fax: +64-3-365-1388; e-mail: [email protected].

The structural characteristics of roosts can in¯uence the thermal environment (Kurta, 1985; Bell et al., 1986; Barclay et al., 1988) and the degree of exposure to predators (Nilsson, 1984; Tideman and Flavel, 1987; Morrison, 1979). The physical size can set limits on the numbers of bats using the roost and so a€ect their social organisation (Kunz, 1982). Only the `tent-making' bats (Timm and Mortimer, 1976), are known to manipulate the physical structure of their roost environment, so for most bat species the active selection of roost characteristics could in¯uence survival and reproductive ®tness. Furthermore, the availability of suitable roosts can also limit bat distribution and population size (Findley and Wilson, 1974; Humphrey, 1975; Findley, 1993). The New Zealand long-tailed bat (Chalinolobus tuberculatus Gray 1843, Vespertilionidae) is one of only two extant bat species living in New Zealand. It is an endemic species belonging to an Australasian genus which includes ®ve other species. In terms of its conservation status C. tuberculatus is classed as Vulnerable

0006-3207/99/$Ðsee front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0006 -3 207(98)00069 -X

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(= threatened; Bell, 1986). It is a moderately small (8± 10 g) insectivorous bat which is largely forest dwelling, gives birth to a single young once a year and roosts either solitarily or in colonies containing up to several hundred individuals (Daniel, 1990). Information on roosting ecology and habitat requirements is currently being sought in an e€ort to better understand the threats which New Zealand bats face (Molloy, 1995). There has been little published characterising C. tuberculatus roosts. The most well known and best described roost is in Grand Canyon Cave, North Island, which is occupied throughout the year by up to 300 bats (Daniel and Williams, 1983). Records of bat roosts throughout New Zealand were compiled by Daniel and Williams (1984). Of the 52 C. tuberculatus roosts reported, 31 were in trees (native and introduced species), 12 were in caves and nine were in buildings (farm sheds, bridges and a boat jetty). Most of the roosts inside buildings were found in autumn or winter and contained only a single torpid bat. No nursery colonies were found in buildings. More recently, Griths (1996) described roosts of C. tuberculatus in a predominately agricultural landscape with highly fragmented indigenous forest remnants in South Canterbury, South island. Anecdotal reports from this area were of roosts in barns and sheds. By contrast none of the 23 roosts Griths located in his radio-tracking study were in buildings. Eighteen were in small inconspicuous limestone crevices and ®ve were in trees. These roosts contained very small numbers of bats (1±10) and Griths found no evidence of breeding during his 2 two year study. These studies show that trees are frequently used as roosts in highly modi®ed landscapes and a recent study of roosting behaviour (C. O'Donnell and J. Sedgeley, unpublished data) clearly demonstrates the importance of trees to C. tuberculatus for roosting and breeding in unmodi®ed forest areas. Despite this, little attention has been given to describing tree roosts in any detail. If C. tuberculatus require a highly specialised roost environment traditionally provided by trees, the reduction of indigenous forest may be forcing them to use less than optimal roost sites. Prolonged use of unsuitable roosts can reduce survival and productivity and may reduce the viability of a bat population (Brigham and Fenton, 1986). Large scale clearance of lowland forests over the last 1000 years has destroyed an enormous proportion of wildlife habitat in New Zealand. Indigenous forest once covered 90% of New Zealand (McGlone, 1989), but is now reduced to an estimated 14% of its original area (Stevens et al., 1988). Current programmes of selective logging may continue to threaten bat populations in local areas (Molloy, 1995). Certainly cavitynesting forest birds are particularly vulnerable to the e€ects of selective logging (O'Donnell, 1991; O'Donnell and Dilks, 1994) which targets older and larger trees (O'Donnell and Dilks, 1987).

Roost selection is best determined by comparing bat's roost sites with the characteristics of available sites (Barclay et al., 1988; Taylor and Savva, 1988; Lumsden et al., 1994; Lunney et al., 1995; Campbell et al., 1996; Vonhof and Barclay, 1996; Entwhistle et al., 1997). We examined roost selection as part of a broad study of C. tuberculatus roosting ecology in temperate rainforest. In this paper we: (1) describe the roost sites of C. tuberculatus, (2) determine whether C. tuberculatus selects roosts on the basis of landscape (e.g. landform, forest type, forest structure) and tree characteristics (e.g. species, age, size); (3) evaluate how the availability of suitable roosts may limit C. tuberculatus populations and discuss implications for conservation. 2. Methods 2.1. Study area The study was conducted in the lower Eglinton Valley, Fiordland National Park in the South Island, New Zealand (44 580 S, 168 010 E). The valley is glaciated with steep sides and a ¯at ¯oor, 0.5±1.5 km wide, at c.250±550 m a.s.l. Tussock grasslands cover much of the valley ¯oor, although the composition has been modi®ed by the e€ects of grazing (cattle and sheep) and over-sowing with introduced grass species. Temperate southern beech (Nothofagus) forest covers gentle glacial terraces and outwash fans on the lower hill-slopes and then rises steeply to the timberline at 1000±1200 m a.s.l. A road bi-sects the valley for its entire length. Annual rainfall averages 2300 mm per year in the centre of the valley, but increases up to >5000 mm per year further up the valley. Red and silver beech (Nothofagus fusca, N. menziesii) dominate the forest on the valley ¯oor. Forest composition varies, ranging from pure stands of silver beech c. 20 m tall along the forest margin to tall stands of red beech up to c. 60 m tall further into the forest. Mountain beech (N. solandri var. cli€ortioides) occasionally contributes to the canopy at low altitudes, and becomes more common with increasing altitude. Under the canopy the forest is generally open with few understorey plants and a ground cover of mosses. The most common understorey plants are mountain toatoa (Phyllocladus aspleniifolius var. alpinus), broadleaf (Griselinia littoralis) and Coprosma spp. 2.2. Capture of bats and location of roosts Roosts were found over four years (late spring±early autumn, October±March 1993±1997), by following radio-tagged bats. C. tuberculatus were caught in canopy-height mist-nets set in the forest (Dilks et al., 1995). To maximise capture rates, nets were erected

J.A. Sedgeley, C.F.J. O'Donnell/Biological Conservation 88 (1999) 261±276

close to forest-grassland edge and forest gaps along the lower 10-km of the valley ¯oor in an area where acoustic bat surveys (C. O'Donnell, unpublished data) had revealed relatively high intensity of bat-use. Up to nine canopy-rigs were used per night, each with between six and eight 12.82.1 m mist-nets covering an area 2±20 m high. Bats were ®tted with 0.7 g transmitters (BD2A, Holohil Systems, Canada). Transmitter weight represented 6.7% of average female body weight, and 7.6% of average male body weight, and were attached between the scapulae using a latex-based contact adhesive glue (F21, Ados Chemical Company. New Zealand) after the fur had been partially trimmed. The sample of age and sex classes of bats radio-tagged and followed each month was dependent on the composition of bats caught in mist-nets. Because densities of foraging C. tuberculatus were low, and they could detect mist-nets, catch rates were extremely low (<0.01 bats per net h). Constraints on available personpower meant that only 2±4 bats could be followed intensively at one time. Nets were opened on ®ne, calm nights for up to two weeks per month and ®ve hours per night in an e€ort to keep a sample of four bats with transmitters on at any one time. Trees containing bat roosts were located during the day by radio-tracking using a TR4 receiver (Telonics, Az, USA) and a 3-element hand-held yagi aerial (Sirtrack, Havelock North, New Zealand). Roost cavities were identi®ed either by observers on the ground watching bats ¯ying into the roost tree at dawn or ¯ying out at dusk. Alternatively, the tree was climbed using a single rope technique (O'Donnell et al., 1996) and the TR4 receiver was used at close range to identify the occupied cavity. 2.3. Roost tree characteristics The location of each roost tree identi®ed was recorded as a six ®gure grid reference (New Zealand Map Series 1, S131, 1978). Where possible we measured eight characteristics for each roost tree. We recorded tree species and classi®ed it as alive or dead (>90% dead limbs and loss of foliage=dead tree). Tree girth (stem diameter at breast height, DBH) was measured as an indicator of tree size and age. Where stem shape was irregular we applied standards out-lined in Alder and Synnott (1992). We measured overall tree height, trunk height (the distance to the ®rst canopy height branch=crown point height, Alder and Synnott, 1992), and height of cavities from ground with a clinometer (Suunto, Helsinki, Finland). Trunk surface area, an indicator of potential habitat area available for cavity formation, was calculated as pDBHtrunk height (adapted from Elliott et al., 1996). Binoculars were used to estimate the number of cavities visible from the ground per tree. It was largely impossible to access cavities in

263

the tree crown, and too subjective to assess from the ground. So, all cavities recorded are those occurring on the main trunk and lower main limbs. To assess the accuracy of our counts we climbed 43 randomly-selected trees and counted cavities present on the trunk and lower limbs and compared them with counts we had previously made from the ground. There was no signi®cant di€erence between the number of cavities observed using each method (Mann±Whitney U=821, p=0.37). Canopy closure was assessed from the base of the tree and visually estimated to the nearest 5%. A mean error of 3.7%‹3.85 SD was detected between two independent observers estimating the canopy closure of 50 randomly selected trees. Canopy closure and height measurements were measured as indicators of the accessibility and exposure of roost entrances. 2.4. Roost site characteristics (roost plots) We de®ne roost site to be the immediate area surrounding a tree which contains a bat roost. To describe general landscape characteristics at roost sites we measured four variables, ground slope, altitude, distance of roost tree from forest edge and density of potential roost trees/ha (overall tree density, frequency of tree species and density of each tree species on standard plots). Ground slope was measured on site with the clinometer. The distance from forest-grassland edge was also measured on site, but altitude was estimated from the map. Density of potential roost trees/ha was calculated by measuring the distances to the nearest four available trees around each of a sub-set of 121 roost trees (pointcentred quarter method, Causton, 1988) (cf. Finch, 1989). Since our sampling techniques were retrospective we were able to limit our measurements of trees to those which we considered to be potential roost trees (i.e. available to bats). We used the minimum dimensions observed for stem diameter and total height of roost trees as a guideline to determine the lower limit acceptable for an available tree (cf. Smith, 1997). The smallest stem diameter of a tree containing a bat roost was 27 cm, and the lowest total height was 1.7 m (a dead stump). Thus, our sample of available trees was limited to trees with stem diameters of 20 cm and total heights of 1.0 m. Additionally, to test if roost tree features might be associated with a local habitat or forest structure we measured the eight tree characteristics (listed for roost trees above) for each of the four available trees. This sub-set of roost trees and associated available trees are hereafter termed roost plots. 2.5. Characteristics of random trees available to bats (random plots) We measured random bat-available trees as a control sample to assess how use of certain tree and landscape

264

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characteristics compared with availability. Trees were sampled throughout the roosting area using the pointcentred quarter method, which is particularly suitable for surveying trees (Curtis and McIntosh, 1950; Causton, 1988). A road runs through the middle of the study area and we marked out transect lines along compass bearings at 100 m intervals at right angles to the road, extending from 0±500 m into the forest on each side. The transects were tagged at 50 m intervals. One hundred and ®fty sampling points (point-centres) were established at random directions and distances from the 50 m tags. These sampling units are hereafter termed random plots. We marked four quadrants around each point-centre and located the nearest available tree in each quadrant. The eight tree characteristics (see roost trees above) were described for each tree and distance from the point-centre to each tree was used to calculate potential roost tree density/ha (as above) (Causton, 1988). The roosting area was divided into 500 m distance bands from the forest-grassland edge up to the timberline on a map. The area of forest in each band was measured with a digital planimeter (Planix2) to determine the area (ha) of available forest in each distance and altitudinal classes. 2.6. Data analysis Initially univariate statistics were used to test if there were di€erences between characteristics of sites used by bats and those available. Non-parametric Mann±Whitney U-tests and Kruskal±Wallis H-tests were used to compare samples where data sets were not normally distributed (tested with Wilks±Shapiro Statistic W). Two-sample ttests and one-way analysis of variance were used when distributions were normal and sample variances similar. Chi-squared tests were used to test di€erences in the frequency of occurrence of characteristics between the two sets of data (used and available) (Sokal and Rohlf, 1981). Spearman rank rs correlation coecients were used to test for correlation between roost site variables. Logistic regression (Statistix for Windows, Analytical Software, Tallahassee, FL, USA) was used to determine which of the tree or site features associated with the trees the bats used best explained any apparent selection. Logistic regression is particularly suitable for habitat association studies when habitat variables often have non normal distributions, are categorical, and the sampling design is retrospective (Ramsey et al., 1994). Logistic regression is based on modelling presence and absence data. For the purpose of this analysis we used the random data (available trees) to represent absence, and assumed the available trees were not being used by bats. Firstly, a set of variables (tree characteristics) was ®tted to the model. Then the signi®cance of individual variables was tested by removing one variable at a time from the model whilst leaving all others in place.

3. Results 3.1. Bats radio-tracked A total of 73 bats was radio-tracked, 13 were followed during 1993±1994, 18 in 1994±95, 29 in 1995±96 and 13 in 1996±1997. Their sex and age composition was 14 adult males, 34 breeding females, nine nulliparous females (non-breeders who had not previously given birth) and 16 juveniles. Bats were followed for as long as the transmitters remained attached or functional (an average of 11.9‹6.4 SD days, range 1±28 days) and they led us to 291 roost trees. 3.2. Landscape characteristics of C. tuberculatus roost sites 3.2.1. Di€erences between roost plots and random plots We measured characteristics of 484 trees from 121 roost plots and 593 trees from 150 random plots (the full quota of 600 possible tree measurements was not obtained, because occasionally there were no trees present in some of the quadrants close to the forest edge). Six tree species were recorded; red beech, silver beech, mountain beech, broadleaf, matai (Podocarpus spicatus) and Hall's totara (P. halli). All dead trees were beech but, with little or no bark present, identi®cation to species level was not reliable. All the dead trees found were small stumps or trees with no foliage, few limbs and no observable live wood. With such distinctive features, dead trees were treated as a seventh `species' category. The frequency of occurrence of tree species varied signi®cantly between roost and random plots (w2=14.45, df 3, p<0.01). Matai, broadleaf and totara were excluded from this analysis because of small sample sizes. Roost plots were composed of more red beech and less mountain beech than were random plots (Table 1). Tree density was signi®cantly lower around roost trees (median=213/ha) than in random plots (median=298/ha, Mann±Whitney U=4986, p<0.001). Most of this di€erence can be attributed to the higher density of red beech trees on random plots (Table 1). There were no signi®cant di€erences in the average stem diameter, total tree height, trunk height, percentage canopy closure, average number of holes per tree, height of holes from ground and trunk surface area between trees on roost plots and trees on random plots Mann±Whitney U-tests and t-tests p>0.05). Consequently available trees measured on roost plots will be ignored in further analysis and roost trees will be compared with available trees from random plots only. 3.2.2. Distance from forest edge, slope and altitude The area in which roosts were found was comprised of two forested valley sides of c. 4036 ha divided by c. 830 ha of tussock grassland and river bed on the valley

J.A. Sedgeley, C.F.J. O'Donnell/Biological Conservation 88 (1999) 261±276

265

Table 1 Frequency of occurrence and density of tree species (20 cm dbh) for roost plots (n=121 plots, 484 trees) and random plots (n=150 plots, 593 tree) Frequency(%) Tree species Red beech Dead beech Silver beech Mountain beech Matai Broadleaf Totara Total

Roost plot 65.7 9.1 22.7 2.1 0.0 0.2 0.2 100

Stem density/ha

Random plot 60.4 9.3 22.9 6.9 0.5 0.0 0.0 100

Roost plot

Random plot

U

140.0 19.4 48.4 4.4 0.0 0.4 0.4

180.0 27.6 68.3 20.6 1.5 0.0 0.0

6340*** 8536 ns 8664 ns 7741 ns

213

298

Stem density compared using Mann-Whitney U-tests (ns=p>0.05, ***=p<0.001).

¯oor. The forest edge on the valley ¯oor was 275 m a.s.l. and low altitude forest extended for 300±500 m across the ¯at valley ¯oor and low river terraces before rising steeply for 2.5±3 km up to the timberline at 1050 m a.s.l. No roosts were found above the timberline and all were located inside the forest, except one, in a tree in grassland 15 m from the forest edge. Ninety-®ve percent of all roosts occurred at low altitude (275±500 m a.s.l) and were 500 m from the forest-grassland edge (median=120 m, range=0±2 000 m). Forest this close to the grassland edge made up only 22% of the available forest in the study area. C. tuberculatus actively selected roost trees in this zone (Chi-squared goodness of ®t test w2=258.91, df 1, p<0.001 comparing frequency of roosts <500 m from the forest edge and >500 m from

the forest edge with expected frequencies) (Fig. 1). Most roost trees (74%) were located on ¯at ground or on slopes of 1±5 (median=0 range=0±7 ). 3.3. Tree characteristics 3.3.1. Roost type Three hundred and four day roosts were found in 291 di€erent trees, but it was not always possible to measure all characteristics of all roosts. Four `species' (including dead trees) of trees were used as day roosts, red beech (n=181, 74%), dead beech (n=55, 22%), silver beech (n=9, 4%) and mountain beech (n=1, <1%). The overall frequency of occurrence of tree species used as roosts was non-random with respect to availability

Fig. 1. Distance of bat roosts from the forest edge (m) compared with available forest (Chi-squared test, w2=258.91, df 1, p<0.001).

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(w2=79.34, df 3, p<0.001). Red beech made up 61% of available trees, dead beech 9%, silver beech 23% and mountain beech 7%. C. tuberculatus used red beech (w2=13.2, df 1, p<0.001) and dead beech (w2=24.14, df 1, p<0.001) more frequently than expected when compared with availability and used silver beech (w2=56.59, df 1, p<0.001) and mountain beech (w2=22.23, df 1, p<0.001) less than expected. In addition to roosts located by radio-tracking, the presence of bat droppings and insect remains enabled us to identify three non-tree roosts, two in buildings and one beneath a rock overhang. The latter roost simply consisted of a large boulder in the forest which formed an overhang one metre above the forest ¯oor, forming a very open and exposed roosting space. The other two roosts were found in small wooden outside toilets situated in campgrounds. It is likely that these sites were used as night roosts or feeding roosts. The droppings were presumed to be those of C. tuberculatus because the roosting range of the other bat species present in the valley, the short-tailed bat (Mystacina tuberculata), occupied an area c. 17 km to the north (C. O'Donnell et al, unpublished data). Radio-tracking also revealed that C. tuberculatus occupied temporary tree roosts during the night, although the exact trees were not identi®ed. Night roosts and non-tree roosts are not discussed further.

comparison of means, p<0.05). The height of available beech trees followed the same trend (Table 2). Ninetyone percent of red beech trees used as roosts were 26 m tall, but only 67% of available trees were in the same height class (Fig. 3). Fifty percent of dead beech roost trees were 26 m high, compared with 4% of available dead beech (Fig. 3). Sample sizes for silver and mountain beech were too small for analysis. Trunk heights of roost trees were also signi®cantly higher than those of available trees (Table 2). The mean trunk height of roost trees did not vary between red, dead and silver beech (Tukey's pairwise comparison of means, p>0.05), The mean trunk height of available beech trees di€ered signi®cantly between tree species (F4,586=43.32, p<0.001), with red beech having the tallest trunks and dead beech having the shortest (Tukey's pairwise comparison of means, p<0.05) (Table 2). The di€erence in trunk height between roost and available trees was due to the large proportion of short dead beech trees in the sample of available trees. Roost trees had signi®cantly larger trunk surface areas than available trees (Table 2). Average trunk surface area did not di€er between species of roost tree (H3,105=7.59, p>0.05). Available red beech trees had signi®cantly larger surface areas than silver beech, dead beech and mountain beech (H4,586=159.78, p<0.001) (Table 2).

3.3.2. Canopy closure Bats selected trees to roost in which had a signi®cantly more open canopy than available trees (Table 2). For roost trees there was no signi®cant di€erence in the average canopy closure between tree species (H3,113=6.79, p>0.05). However, the canopy closure of available red and silver beech was signi®cantly higher than that of dead and mountain beech (H4,588=39.27, p<0.001). Only 51% of roost trees had a canopy closure of 80% compared with 75% of available trees.

3.3.4. Number of cavities per tree and height of cavities from the ground Roost trees had signi®cantly more cavities per tree than did available trees (Table 2) (Fig. 4). Dead beech trees used as roosts had the most cavities per tree (H3,103=17.39, p<0.001). More than half of available trees had no cavities (i.e. 55% of red beech, 57% of dead beech and 79% both mountain and silver beech). Of those that did have cavities, red and silver beech had the most and mountain beech the least (H4,395=23.21, p<0.001). The height of cavities from the ground was measured for a subset of available trees (Table 2) and the cavities measured on roost trees were the actual cavities used as roosts. Roost cavities were signi®cantly higher than random cavities (Table 2). There was no signi®cant di€erence in the height of roost cavities between tree species (H3,188=4.1, p>0.05). Eighty-®ve percent of roost cavities were over 10 m above the ground. Bats did not use basal hollows of tree trunks. Only one roost cavity was less than 5 m from the ground (Fig. 5), and it was located in a dead tree stump situated on the edge of a cli€. Therefore its e€ective height in relation to a bat's ¯ight-path may have been much greater. The roost was occupied by a single bat.

3.3.3. Size of Trees Roost trees had signi®cantly larger stem diameters than available trees (Table 2). The mean stem diameter of roost trees di€ered between tree species (F3,233=10.28, p<0.001), with red beech having the largest stems, and silver beech having the smallest (Tukey's pairwise comparison of means p<0.05). Available tree species exhibited a similar trend (Table 2). Eighty percent of red beech roost trees had stem diameters of 80 cm DBH (Fig. 2), but only 34% of available red beech trees were in this size class. A similar trend was shown for dead beech. Bat roosts were rare in silver beech but occurred in a range of stem diameter size classes (Fig. 2). Roost trees were signi®cantly taller than available trees (Table 2), but were not emergent above the canopy. Mean height di€ered between species of roost tree (F3,232=22.67, p<0.001), with red beech being the tallest and dead beech the shortest (Tukey's pairwise

3.3.5. Tree characteristics associated with selection Many of the tree characteristics measured were associated with selection of roost sites by C. tuberculatus.

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Table 2 Comparison of average (mean‹1SD, median) characteristics for roost trees and available trees, using (a) two-sample t-tests and (b) Mann-Whitney U-tests Characteristic

Roost trees

Available trees

Mean

n

Mean

n

p

Stem diameter DBH (cm) Red beech Dead beech Silver beech Mountain beech Matai

111‹36 93‹78 58‹32 81 ±

172 55 9 1 0

73‹38 63‹38 40‹18 53‹25 44‹12

358 55 136 41 3

<0.001a <0.001a 0.13a ± ±

Overall

105‹36

237

63‹36

593

<0.001a

Total tree height (m) Red beech Dead beech Silver beech Mountain beech Matai

33‹7 24‹8 30‹8 25 ±

172 54 9 1 0

30‹9 9‹7 23‹7 23‹7 20‹7

356 55 136 41 3

<0.001a <0.001a 0.003a ± ±

Overall

31‹8

236

26‹10

591

<0.001a

Trunk height (m) Red beech Dead beech Silver beech Mountain beech Matai

17‹5 19‹5 15‹3 4 ±

81 24 5 1 0

17‹6 9‹5 13‹5 13‹6 13‹5

356 55 136 41 3

0.635a <0.001a 0.364a ± ±

Overall

17‹5

111

15‹6

591

<0.001a

Height of cavities from ground (m) Red beech Dead beech Silver beech Mountain beech Matai

(cavities used as roosts) 17‹7 135 10‹5 16‹7 48 6 13‹4 8 6 13 1 13 ± 0 ±

135 1 1 1 0

<0.001a ± ± ± ±

Overall

17‹7

185

10‹5

138

<0.001a

Median

Range

n

Median

Range

n

p

Number of cavities per tree Red beech Dead beech Silver beech Mountain beech Matai

3 5 2 4 ±

1±10 2±13 1±3 ± ±

78 23 5 1 0

0 0 0 0 0

0±8 0±6 0±8 0±1 0±1

244 39 95 19 3

<0.001b <0.001b 0.002b ± ±

Overall

3

1±13

107

0

0±8

400

<0.001b

Percent canopy closure Red beech Dead beech Silver beech Mountain beech Matai

80 70 75 95 ±

40±95 20±95 60±90 95 ±

84 26 6 1 0

88 75 85 80 80

10±95 25±95 20±95 20±90 75±95

358 55 136 41 3

<0.001b 0.255b <0.035b ± ±

Overall

80

20±95

117

85

10±95

593

<0.001b

Trunk surface area (m ) Red beech Dead beech Silver beech Mountain beech Matai

49 54 19 10 ±

18±167 10±106 15±85 10 ±

79 24 5 1 0

35 9 14 18 14

3±167 3±80 2±68 2±44 3±27

356 55 136 41 3

<0.001b <0.001b 0.039b ± ±

Overall

50

10±167

109

24

2±167

591

<0.001b

2

268

J.A. Sedgeley, C.F.J. O'Donnell/Biological Conservation 88 (1999) 261±276

However, there were many intercorrelations between them. For example, stem diameter was strongly correlated with number of cavities (rs=0.549, p<0.001) and tree height (rs=0.521, p<0.001); trunk height was positively correlated with tree height (rs=0.699, p<0.001); and trunk surface area with number of cavities (rs=0.403, p<0.001). Logistic regression was used to determine which tree characteristics were associated with selection.

Three variables, number of cavities, trunk surface area and canopy cover signi®cantly contributed to the explanatory power of the logistic regression, while DBH, tree height and tree species contributed no additional explanation (Table 3). Therefore, the model indicated that the probability of bats roosting in a tree increased as the number of cavities and trunk surface area increased and canopy cover decreased.

Fig. 2. Stem diameter (DBH cm) of bat roost trees compared with available trees.

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4. Discussion 4.1. Evidence for roost selection Chalinolobus tuberculatus selected roosts on the basis of landscape, forest composition and tree characteristics.

269

Few roosts were found at higher altitude or on steep hill slopes. Most were in the low altitude forest on the valley ¯oor 500 m from the forest-grassland edge. Roosts may have been concentrated in this zone because (a) the forest was more sheltered and less subject to weather extremes (cf. Law. 1993; Lunney et al., 1995),

Fig. 3. Total tree height (m) of bat roost trees compared with available trees.

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J.A. Sedgeley, C.F.J. O'Donnell/Biological Conservation 88 (1999) 261±276

(b) commuting distances were lessened between roosts and the open and forest edge habitats they feed in (C. O'Donnell, unpublished data) and/or (c) the forest on the valley ¯oor contained signi®cantly more suitable roost trees. Red beech forest is associated with fertile soils on lower valley slopes, and in the Eglinton Valley it dominates the valley ¯oor and the roosting area. Red beech forests have lower stem densities/ha and more large diameter stems than both silver and mountain beech forests. Mountain beech is associated with poorer soils and higher altitudes, it tends to have a higher stem

density/ha and to be shorter in height (Wardle, 1984). It is a common timberline species, and so dominates the steep valley sides. Forest structure tends to be de®ned by the distribution of tree characteristics such as stem diameter (Wardle, 1984). There were no signi®cant di€erences in the distribution of DBH, tree height, trunk height, canopy closure and trunk surface area between trees on the two plot types. This suggests that forest structure was relatively homogeneous throughout the roosting area, as would be expected within forest on the valley ¯oor and

Fig. 4. Number of cavities per tree of bat roost trees compared with available trees.

Fig. 5. Comparison of the height from the ground (m) of bat roost cavities and available cavities in red beech trees.

J.A. Sedgeley, C.F.J. O'Donnell/Biological Conservation 88 (1999) 261±276 Table 3 Results of logistic regression of bat roost trees against habitat variables expressed as change in deviance as individual variables were removed from the model whilst leaving all others in place Variable

Full model (six variables) Number of cavities Trunk surface area Canopy cover DBH Tree height Tree speciesa a

Reduction in deviance (w2)

df

p

311.96 137.21 19.14 13.84 0.72 0.21 2.24

4 1 1 1 1 1 4

<0.001 <0.001 <0.001 <0.001 >0.05 >0.05 >0.05

Red beech, dead beech, silver beech and mountain beech.

lower hill slopes. However, roost plots had a signi®cantly lower tree density relative to random plots, inferring that roost trees were associated with more open-structured parts of the forest. We did not measure trees with <20 cm DBH and so our measure of overall forest density is under estimated. The trees with small DBHs were also relatively short and were not as high as bat roosts, therefore the forest can still be termed `open-structured' in relation to roost entrance accessibility. C. tuberculatus selected tall, large diameter red beech and standing dead trees for their roosts, and selected

271

against mountain and silver beech. Several other bat species have been shown to roost preferentially in particular tree species (Table 4). However, the logistic regression model generated in this study indicated that C. tuberculatus did not discriminate between tree species per se, but selected trees on the basis of functional characteristics associated with these trees (i.e. high availability of cavities, greater trunk surface area and relatively low canopy cover). In the Eglinton Valley red beech are the largest beech forest tree, in terms of both total height and stem diameter. Bennett et al. (1994) noted that in Eucalyptus trees the number of cavities increased with stem diameter, but the slope of the relationship di€ered between tree species. Similarly, across all tree species in the present study the number of cavities was correlated with increasing stem diameter, trunk height and trunk surface area. Trees with large surface areas are likely to be more susceptible to weathering and consequent cavity formation. Therefore, it seems to a large extent bats were selecting red beech trees because they were the largest trees. Tree size is not the only factor associated with cavity formation. An additional feature of red beech which may contribute to its higher incidence of cavities is its higher susceptibility to decay. In one study (Litchwark, 1978), pathological wood (a defective core) was present in 92% of red and 68% of silver beech sampled. Some of the red beech also had a pathological wood of a type not found in silver beech. A large proportion of timber

Table 4 Review of research investigating selectivity in temperate tree roosting micro-chiropteran bats Bat species

Selected characteristic 1 2 3 4 5 6

Chalinolobus morio Lasionycteris noctivagans Nyctophilus gouldi Eptesicus regulus, E. sagittula, Chalinolobus morio, Nyctophilus geo€royia Myotis daubentoni, M. mystacinus/brandti M. natterei, Nyctalus leisleri, N. noctula, Pipistrellus pipistrellus, Plecotus auritusa, Nyctophilus geo€royi Chalinolobus gouldii Lasioncyteris noctivagans Myotis sodalis Myotis septentrionalis Eptesicus fuscus Lasionycteris noctivagans Eptesicus fuscus, Lasionycteris noctivagans, Myotis evotis, M. volansa Chalinolobus tuberculatus

+ ++ 0 ++ 0 +

7

Country

Source

+a

Australia Canada Australia Australia

Lunney et al. (1985) Barclay et al. (1988) Lunney et al. (1988) Taylor and Savva (1988)

+a

The Netherlands

Limpens and Bongers (1991)

Australia Australia USA USA USA Canada Canada Canada

Lumsden et al. (1994 and pers. comm.) Lumsden et al. (1994 and pers. comm.) Campbell et al. (1996) Kurta et al. (1996) Sasse and Pekins (1996) Vonhof (1996) Vonhof (1996) Vonhof and Barclay (1996)

+

+

+ + + + +++++ 0 ++ 0 +++++ + + + + + + +b + + + + 0 0 +b + + + + + + +b +++++

+ac New Zealand

This study

1=Tree species, 2=Larger stem diameters, 3=Taller tree height, 4=Lower canopy closure/lower clutter around tree, 5=Dead trees/heavily decayed, 6=More bark cover, 7=Other. (a) older trees, (b) shorter distance to nearest available roost sized tree, c) longer distance to nearest available roost sized tree. +=Positive selection, 0=Used at random or avoided, a blank space denotes that a characteristic was not measured or was not compared with availability. a Data pooled from several species.

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defects in beech trees (butt rots, stem rots, pathological wood) which can result in eventual tree mortality, are caused by attacks of wood boring beetles, (the pinhole borers, Platypus spp.) and a fungus associated with its attacks (Wardle, 1984). Platypus attacks are positively correlated with stem diameter and tree growth rate and attacks on red beech can be 8±9 times more numerous than on silver beech (Litchwark, 1978). In a review of research investigating selectivity m temperate tree-roosting microchiroptera, bats selected roost trees with larger stem diameters (where it was measured) in all the studies reviewed (Table 4). Such a preference has also been shown by other tree cavity roosting mammals (e.g. possum and glider species, Smith and Lindenmayer, 1988) and birds (e.g. mohua, Mohoua ochrocephala, and yellow-crowned parakeets, Cyanoramphus auriceps, Elliott et al., 1996; and woodpeckers, Dendrocopus major, Smith, 1997). Stem diameter is correlated with bark thickness (Wardle, 1984) and degree of insulation (Sluiter et al., 1973; Maeda, 1974; Alder, 1994). Therefore large trees may also o€er the best insulated cavities in the study area. Rieger (1996) demonstrated that di€erent tree species radiated varying levels of heat and that Daubenton's bat (Myotis daubentoni) most often roosted in the tree species which retained heat the longest. The thicker or more ®ssured that bark is, the greater insulation it provides (Nicolai, 1986). Adult red beech has the thickest and most ®ssured bark of all four species of beech in our study area. Silver beech has much thinner, less ®ssured bark and has a lower wood density than red or mountain beech (Wardle, 1984). However C. tuberculatus also roosted in dead trees which had little or no outer bark. Dead trees are unlikely to be as well insulated as live trees due to the lack of bark and also because they have a lower water content (Maeda, 1974). Bats of di€erent sex and age classes often select roosts with di€ering micro-climates, and di€erences are usually explained by di€ering thermoregulatory requirements of these bats, which can also change with time (cf. Watkins and Schump, 1981, Hamilton and Barclay, 1994). Fifty-two percent of C. tuberculatus roost trees were occupied by communal groups of bats and 48% were occupied by solitary bats. Breeding females tended to dominate communal groups, with adult males more frequently roosting alone (C. O'Donnell and J. Sedgeley, unpublished data). Of the total number of roosts found, proportionately more solitary roosts (34%) were found in dead trees compared with communally occupied roosts (19%) (w2=5.37, df 1, p<0.05). We predict that trees of di€erent species, sizes and condition (alive or dead) will provide cavities with di€ering micro-climates and C. tuberculatus will utilise cavities which best suit their current energetic status. Cavity size and shape may directly in¯uence the number and social organisation of bats occupying the

cavity (Kunz, 1982), the roost micro-climate (Kurta, 1985), and the ability of bats to thermoregulate behaviourally (Trune and Slobodchikof, 1976; Roverud and Chappell, 1991). Consequently these factors may e€ect reproductive ®tness (Racey, 1973; Tuttle and Stevenson, 1982). Since the diameter of a trunk or branch is likely to determine the size of the cavity within it, we predict that during the summer months, trees with larger stem diameters are most likely to provide cavities which meet C. tuberculatus's social, thermoregulatory and reproductive requirements. Although most C. tuberculatus roosts were in live trees, dead trees were used as roosts in a higher proportion (22%) relative to their abundance in the forest (9%). Several other bat species selectively roost in dead trees (Table 4), including two other Chalinolobus species, C. gouldi (Lumsden et al., 1994) and C. morio (Taylor and Savva, 1988). C. gouldi showed a similar bias in the use of dead trees (30% compared with the 6% available) (Lumsden et al., 1994) to that found for C. tuberculatus in the present study. Strong selection for roosts in dead trees has also been found in birds (Saunders et al., 1982; Raphael and White, 1984; Smith, 1997). Generally, large standing dead trees have numerous cavities (the larger a tree is at time of death the longer it will stand and the longer it stands more cavities develop, Newton, 1994). Given the prediction that dead trees are less well insulated (above), selection of dead trees by C. tuberculatus may simply re¯ect the relative abundance of potential roost cavities (see Table 2). In mixed silver and red beech forest there is signi®cantly more (15%) dead red beech/ha than dead silver beech/ ha (5%) (Litchwark, 1978). Dead trees may also have been selected as roosts because they have fewer branches and thus relatively uncluttered surroundings with improved access immediately outside roost cavities. Selection of roosts in the highest cavities and the tallest trees in open-structured forest with low canopy closure is consistent with predictions of bat ecomorphology. On the basis of echolocation call structure and wing morphology, C. tuberculatus has been described as being suited to moderate to fast foraging ¯ight in forest edge and gap habitats, with limited manoeuvrability within dense vegetation (C. O'Donnell, unpublished data). Roost exits that are far from the ground in an area of more open canopy and less dense forest would compensate for lack of manoeuvrability. In addition to selecting trees in more open forest stands we expect C. tuberculatus to occupy cavities with less immediate foliage clutter, as has been found in other studies (e.g. Gaisler et al., 1979; Campbell et al., 1996). Red beech trees tend to have few complex branches on the lower two-thirds of the trunk (see mean hunk height, Table 2), whereas branches of mountain and silver beech trees can extend more than half-way down the main hunk (Wardle, 1984). Free ¯ight space in front of the roost

J.A. Sedgeley, C.F.J. O'Donnell/Biological Conservation 88 (1999) 261±276

entrance is particularly important for newly volant bats which need a greater vertical space in which to practice ¯ying (Constantine, 1966). 4.2. Are roost sites limiting? C. tuberculatus selected relatively specialised roost sites and roost trees, but as the Eglinton Valley study area consisted of >8000 ha of unmodi®ed beech forest, it seems unlikely that the availability of suitable trees will be limiting in the short term. Seventy percent of C. tuberculatus roosts were occupied for only one day, even in the breeding season, with mothers carrying non-volant young to new roosts (C. O'Donnell and J. Sedgeley unpublished data). Only 10% of roosts were re-used in the same season. Frequent changing of roost sites indicates that roosts are abundant and non-limiting (Kunz, 1982; Lewis, 1995). Providing the National Park retains its protected status, the availability of suitable roosts should continue into the future. However, threats from non-native species present in the National Park, such as the competition from cavity nesting birds (e.g. starlings, Sturnus vulgaris), and the in¯uence of sheep grazing on forest regeneration rates may be of concern. Outside of forested areas and in developed landscapes C. tuberculatus has been reported roosting in a variety of man-made structures and in caves and rock crevices. However, no con®rmed evidence of breeding has been found at any of these locations (e.g. Griths, 1996), which may indicate that they are unsuitable as breeding sites, and used only because suitable roost availability is limited (cf. Brigham and Fenton, 1986). 4.3. Implications for the conservation of bats in managed forests Stem diameter (DBH) did not contribute signi®cantly to the explanatory power of the logistic regression model of roost selection. However, DBH was strongly intercorrelated with characteristics which did contribute signi®cantly. DBH is also directly correlated to tree age, although the relationship between DBH and beech tree age is highly variable, with growth rates being a€ected by numerous interacting factors including, soil fertility and altitude. The importance of stem diameter is highlighted in the studies reviewed in Table 4 where bats clearly selected roost trees with larger stem diameters. Therefore, conservation managers can use measurement of stem diameter as tool to predict whether a tree is likely to contain a bat roost and to evaluate the availability of bat roosting habitat. In addition, a knowledge of the size of stem diameter bats select will aid in assessing the potential impacts of forest management practices. The maximum age for red beech is between 450 and 600 years (Wardle, 1984). One record from the Eglinton Valley estimated a red beech tree with a DBH of 163 cm

273

to be 513‹59 years old (Ogden, 1978), but the maximum DBH of a bat roost tree in this study was 222 cm, inferring that red beech may grow much older. Apart from this record we found no other data relating age to DBH in trees >100 cm. The minimum DBH for a red beech tree used as a bat roost was 40 cm, inferring that the minimum age for red beech bat roost trees is between 60±200 years (Ogden, 1978) or 100 and >200 years (Wardle, 1984). Silver beech may also reach a maximum age of 600 years (Wardle, 1984). The DBH's of silver beech trees used as bat roosts ranged from 33 cm to 136 cm, inferring a minimum age of between 80± 130 years (Stewart, 1986) or 90 and >200 years (Wardle, 1984). The di€erent species have di€ering growth rates; red beech grows faster than silver and so attains a large size earlier (red beech takes 100±120 years to reach the canopy, whereas silver takes 180±200 years to reach the same height, Stewart and Rose, 1990). increased levels of Platypus attacks are associated with higher growth rate (see above). C. tuberculatus clearly selects older-aged trees as roost sites. This preference has been observed in other bat species (Table 4) and in cavity nesting birds (e.g. DeLotelle and Epting, 1988; Rudolph and Conner, 1991; Mawson and Long, 1994). There is no longer any large scale clearfell logging of indigenous forest in New Zealand, however, areas of unprotected lowland forest are still managed for timber production. Our ®ndings suggest that most silviculture practices will reduce the availability of bat roosting habitat because trees which are of sucient size and age to provide suitable cavities are removed (cf. Mackowski, 1984). This is consistent with other studies investigating the e€ects of forest management on wildlife (e.g. Lunney et al., 1988; O'Donnell, 1991. Lindenmayer and Possingham, 1995). In the past, beech forest silviculture aimed to perpetuate an even-aged growth structure, where trees were generally harvested after 60±120 years with DBH's of 45±75 cm (Wardle, 1984). Only 24% of C. tuberculatus roosts are in trees of this size or less, most being in larger trees which exceed the age at which trees are usually harvested. Routine thinning and pruning to produce uniform development of young beech stands, and removal unmerchantable older trees and dead wood to reduce Platypus outbreaks will further reduce cavity formation. Standing dead trees can be removed from New Zealand indigenous forest without the permits required for logging of live trees (Ministry of Forestry, 1997). The number of tree cavities in old growth natural forest containing dead trees can exceed 40/ha, compared with 1±15/ha in managed mature forest with no dead trees (reviewed by Newton, 1994). The more modern practice of selective logging of either single trees or small groups scattered throughout the forest is an alternative to the uniform silvicultural system described above and aims to produce a more natural uneven-aged stand structure. However, this

274

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method still targets the removal of defective and misshapen stems and the large old trees (which bats prefer), and in practice actually inhibits the natural regeneration process. After target trees are removed adjacent canopy trees quickly ®ll in the available gaps that are created and consequently prevent regeneration (Wardle, 1984; Stewart et al., 1992). Selective logging of larger groups of trees is advocated for beech forest as it does favour regeneration (Wardle, 1984). However, removing large patches of trees could impact severely on roosting habitat. Roost trees tended to be clustered close together in our study (C. O'Donnell and J. Sedgeley, unpublished data), so group logging could destroy a large proportion of bat roosts in one operation. The C. tuberculatus population in our study consisted of three distinct subgroups, whose foraging areas almost completely overlapped (O'Donnell, 1995) but whose roosting areas were adjacent but largely exclusive (O'Donnell, unpublished data). Therefore, if a group's roosting area was largely destroyed it may not be able to move into adjacent forest. 5. Conclusions Selection of specialised roost sites and roost trees together with high roost lability and low levels of roost re-use indicate that C. tuberculatus need large forested areas containing large numbers of old trees. Roosting habitat of this type is seldom found in forests managed for timber production or in developed landscapes. Therefore, outside protected forest areas roost sites are likely to be rare, and this may limit the geographical distribution of bat populations. Our results show C. tuberculatus to exhibit clear selection for tall, large diameter, open-structured, low altitude red beech forest. These ®ndings are consistent with the habitat requirements of cavity-nesting New Zealand forest birds (Elliott, 1992; Elliott et al., 1996) and con®rm that unmodi®ed lowland indigenous forests are essential for the continued survival of many threatened wildlife species. Recently protected areas of regenerating secondary forest could be enhanced as bat roosting habitat by the provision of roosting boxes (Fenton, 1970; Stebbings and Walsh, 1985). However, further information on cavity preferences, such as physical size and micro-climate would be of advantage before embarking on such schemes. In the Eglinton Valley, red beech was the tree species which bats most often roosted in. Elsewhere in New Zealand other tree species can reach similar or even greater sizes and ages and may be equally important as roost trees. A study of roost selection in other forest types would be worthwhile and could test the prediction that trees with greater numbers of cavities, larger surface area and lower canopy closure are likely to be used as roosts.

In this paper we have not distinguished between roosts occupied by di€erent numbers, age and sex classes of bats. Because intraspeci®c (Morrison, 1980; Watkins and Schump, 1981; Alder, 1994; Hamilton and Barclay, 1994; Lumsden et al., 1994) and temporal (Barclay et al., 1988; Law, 1993; Lunney et al., 1995) variability in roost selection has been demonstrated in other bats, we will examine these aspects in C. tuberculatus in a future analysis. Data have also been collected on roost cavity characteristics (J. Sedgeley, unpublished data). The next stage of this study will be to test the prediction that C. tuberculatus selects roost cavities with specialised characteristics such as speci®c physical and thermal properties. Acknowledgements Our thanks go to M. Bach, G. Burrell, B. Cairns, E. Christmas, N. Corp, C. Dense, P. Dilks, S. Dymond, D. Eason, G. Elliott, M. Francis, J. Fraser, C. Geddes, D. Geddes, S. Geddes, R. Griths, K. Hellier, F. Jasma, H. Moller, J. Molloy, F. Prott, G. Rasch, W. Simpson, M. Spurr, and B. Zilletti for assisting with radiotracking. A special thank you to J. Christie, J. Comrie, J. Hayes, D. Mawer, J. McMurdo, K. O'Donnell, W. Simpson, B. Theinert, and S. Torr for assisting with tree measuring. The project was undertaken with funding from the Department of Conservation, New Zealand Lottery Grants Board, World Wide Fund for Nature (NZ) (through the Telecom New Zealand Ltd. Conservation Fund), Royal Forest and Bird Protection Society (J. S. Watson Trust and Stocker Scholarships) and the University of Otago. Thank you to Lindy Lumsden, Graeme Elliott, Peter Webb, Glenn Stewart and an unnamed referee for their useful comments on earlier drafts of the manuscript. Thanks also to Graeme Elliott for statistical advice. References Alder, H., 1994. Erste erfahrungen mit dem data logger: EreigniszaÈhlung vor baumhohlenquartieren von wasser¯edermaÈusen, Myotis daubentoni, bei gleiclizeitiger messung mikroklimatischer werte. Mitt. natf. Ges. Scha€hausen. 39, 119±133. Alder, D., Synnott, T.J., 1992. Permanent Sample Plot Techniques for Mixed Tropical Forest. Tropical Forestry Papers No. 25. Oxford Forestry Institute, Department of Plant Sciences, University of Oxford. Barclay, R.M.R., Faure, P.A., Farr, D.R., 1988. Roosting behavior and roost-selection by migrating silver-haired bats (Lasionycteris noctivagans). J. Mammal. 69, 821±825. Bell, B.D., 1986. The Conservation Status of New Zealand Wildlife. New Zealand Wildlife Service Occasional Publication No. 12. Department of Internal A€airs, Wellington, NZ. Bell, G.P., Bartholomew, G.A., Nagy, K.A., 1986. The roles of energetics, water economy, foraging behaviour and geothermal refugia in the distribution of the bat Macrotus californicus. J. Comp. Physiol. B. 156, 441±450.

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