Eur J Wildl Res DOI 10.1007/s10344-014-0862-8

ORIGINAL PAPER

Living above the treeline: roosting ecology of the alpine macrobullaris

Antton Alberdi & Joxerra Aihartza & Ostaizka Aizpurua & Egoitz Salsamendi & R. Mark Brigham & Inazio Garin

Received: 11 June 2014 /Revised: 12 September 2014 /Accepted: 22 September 2014 # Springer-Verlag Berlin Heidelberg 2014

Abstract Little is known about the alpine bat community, but foraging and trophic behaviour, of P.macrobullaris, as well as recent studies suggest that the alpine long-eared bat, Plecotus its distribution pattern linked to mountain regions. macrobullaris, commonly forages in alpine habitats, although most of its known roosting records are from locations situated Keywords Alpine long-eared bat . Mountain long-eared bat . below the treeline. Aiming to contribute to resolving this Pyrenees . Radio-tracking . Sexual segregation . Scree seemingly contradictory pattern of ecological preferences of deposits . Thermoregulation P. macrobullaris, we carried out a radio-tracking study to (1) identify its roosts and unveil its roosting habitat preferences, (2) determine whether found foraging in alpine habitats Introduction do actually roost and breed in such high-mountain environ- ments, and (3) test if any elevation-related sexual segregation The diversity and activity of chiropterans in alpine environ- occurs. We captured 117 alpine long-eared bats and radio- ments may have been underestimated thus far (Alberdi et al. tracked 37 individuals to 54 roosts located at elevations be- 2013). Elevation-gradient diversity and abundance studies tween 1,450 and 2,430 m, 46 of them above the treeline. Bats have shown that chiropteran diversity and activity decreases used rock crevices (30 roosts), scree deposits (21) and build- above mid-elevations (Holzhaider and Zahn 2001), which ings (3) for roosting, and most lactating and pregnant females may have led many elevation-related diversity studies to over- relied on crevices. Bats selected areas with high meadow look the alpine belt (Holzhaider and Zahn 2001;Pavlinicand availability near the roost, while avoiding densely forested Tvrtkovic 2004). However, some recent studies have shown areas. Foraging areas and roosting sites were located at the that bats do exploit alpine environments (Barataud 2005; same elevation, indicating that alpine long-eared bats use Alberdi et al. 2013). Although more than a dozen species have alpine areas for both roosting and foraging in the Pyrenees. been captured or detected above the treeline in Europe (Aellen Breeding females roosted at lower elevations than nulliparous 1962; Barataud 2005; Alberdi et al. 2013), there are few females and males, though they remained above the treeline. known roosting records. The particular physiological require- Although being considerably different to the ecological pref- mentsofbatsmostlikelyhamperthemfromroostingathigh erences described so far in the Alps, the roosting behaviour we elevation. For instance, pregnant and lactating females cannot observed was consistent with some ecological traits, namely take advantage of deep torpor, presumably in order to speed foetal and neonatal development (Dzal and Brigham 2012). It appears that the majority of bats found in alpine environments Communicated by C. Gortázar are primarily lowland species that occasionally commute to higher elevations when conditions become favourable A. Alberdi (*) : J. Aihartza : O. Aizpurua : E. Salsamendi : I. Garin Department of Zoology and Cell Biology, Faculty of Science (Michaelsen 2010) or use alpine environments as commuting and Technology, University of The Basque Country UPV/EHU, routes (Aellen 1962; Alberdi et al. 2012a). Nevertheless, Leioa, The Basque Country, Spain detailed information about the spatial and temporal dynamics e-mail: [email protected] of bats in alpine habitats is still largely unknown. R. M. Brigham The alpine long-eared bat, Plecotus macrobullaris Department of Biology, University of Regina, Regina, Canada (Kuzjakin, 1965), stands out among the bat species reported Eur J Wildl Res in European alpine environments. More than two thirds of the biased view of the actual roosting preferences of the species. bats captured in European supraforestal habitats by Alberdi No study to date has focused on the roosting ecology of et al. (2013)wereP. macrobullaris. The study did not identify P. macrobullaris, and therefore the relative frequency of dif- the pattern of elevation-related sexual segregation reported for ferent roost types remains unknown. many other species (Cryan et al. 2000; Russo 2002), and In order to elucidate the roosting ecology of alpine instead, breeding females were captured up to 1,000 m above P. macrobullaris during the breeding season, we identified the treeline (Garin et al. 2003). Additionally, molecular anal- the roosting locations and determined the types of roosts used ysis of diet showed that P. macrobullaris forage in alpine by individual alpine long-eared bats using radio-tracking. We habitats rather than only using them for commuting (Alberdi tested whether (1) bats select any specific habitat for setting et al. 2012b). However, depending on the geographic area, the their roosts, (2) if elevation differences exist between foraging elevation range of P. macrobullaris spans from sea level up to and roosting sites and (3) if any elevation-related sexual 2,800 m (Alberdi et al. 2013), and this species has been found segregation occurs in their roosting behaviour. This informa- in habitats other than alpine grounds. Two studies carried out tion will allow us to assess whether Pyrenean P.macrobullaris in Switzerland identified a preference towards deciduous for- exhibit a mid-elevation anthropophilic roosting pattern similar est environments (Rutishauser et al. 2012; Ashrafi et al. 2013), to that depicted in the Alps, or conversely, if they behave in a while a population studied in Italy was shown to avoid wood- similar manner to alpine species that both forage and roost in lands (Preatoni et al. 2011). The species has also been cap- the alpine belt. tured in semi-arid steppes and other scarcely vegetated areas (Shehab et al. 2007; Benda et al. 2008). Similarly, current understanding of the roosting ecology of P. macrobullaris is still inconclusive. Most known roosting Methods locations are from the Alps, where the species is commonly found in buildings below the treeline (Presetnik et al. 2009; Fieldwork Mattei-Roesli 2010; Rutishauser et al. 2012), corresponding to the reported use of woodlands as foraging grounds in these This study was performed in July and August 2012, in eight areas. However, the species has also been captured in the valleys scattered throughout the Pyrenees (Fig. 1). The Pyre- alpine belt of several mountain ranges in Europe, far from nees mountain chain separates the Iberian Peninsula from woodlands and where buildings are very scarce (Alberdi et al. continental Europe with elevations ranging from 500 to 2013). These observations suggest that P. macrobullaris 3,400 m amsl. Nets were set following the technique of may use other types of roosting resources, similar to those Alberdi et al. (2013) in 18 sparsely vegetated meadow loca- used by other alpine vertebrates. Several alpine birds rely tions with elevations ranging from 1,550 to 2,370 m, the range on boulders, crevices and ledges for nesting, and a small at which 95 % of known records in the Pyrenees are found number also take advantage of caves (Cramp et al. 1994). (Alberdi et al. 2013). Small terrestrial usually shelter in rock or stone Captured bats were identified in the field using morpho- stacks such as scree deposits (Luque-Larena et al. 2002), logical characteristics (Dietz and Helversen 2004). Bats whereas large mammals tend to shelter close to steep cliffs were sexed and aged by visual inspection, with lactating (Villaret et al. 1997). Roosting at high elevations would females identified by the production of milk after gentle allow bats to be closer to their foraging grounds, but lower pressure on the mammary glands. Bats weighing 8–12 g temperatures may limit breeding females, which are were fitted with 0.35 g radio transmitters (PipII, Biotrack prevented from entering into deep and long torpor when Ltd., Dorset, UK) and released at the site of capture within gestating or nursing their pups (Dzal and Brigham 2012). 20 min of being caught. We tracked the tagged bats to Conversely, roosting at lower elevations would probably diurnal roosts for 8 days, except on the first day after offer females better climatic conditions, but they would tagging, as often as accessibility made it feasible. Based have to fly greater distances when commuting between on the species’ reported foraging range (Arthur and roosting and foraging sites. Lemaire 2009;Preatonietal.2011), a radius of at least Finally, an important factor that must be taken into account 10 km from each capture location was surveyed, mainly on is the substantially lower detectability of bats that roost in foot in areas far from roads or vehicle tracks. We searched natural rock crevices compared to sheltering in caves, for signals from bats in roosts at elevations ranging from and even more so in buildings, which are commonly exam- 1,200 to 2,950 m, covering the montane (dense deciduous ined for research and conservation purposes. In fact, most and/or coniferous forest), subalpine (sparse trees) and al- P. macrobullaris colonies sheltering in buildings have been pine (meadows and sparsely vegetated areas) belts. Exact discovered as a result of extensive building monitoring roost locations were recorded using GPS devices (Oregon programmes (Mattei-Roesli 2010), which may have led to a 550, Garmin, Kansas, USA). Eur J Wildl Res

Fig. 1 Geographic location of the eight valleys where P. macrobullaris individuals were captured and tracked in the Pyrenees

Data analysis assessed using Spearman’s rank correlation coefficient (ρ)and ensured that all pairwise values were below 0.5 (Kutner et al. Radio-tracked bats were grouped into three classes based on 2004). All roost locations were compared to a random set of sex and reproductive condition: breeding (lactating and preg- locations generated within the study area. We used a chi-square nant) females, nulliparous females and males. Roost types goodness-of-fit analysis to test whether habitat composition were classified into four categories: crevices, caves, scree around roosts was significantly different from random. The deposits and buildings. Rock fractures or fissures up to habitat selection analysis was developed using generalised 20 cm wide, regardless of whether they occurred in large cliffs linear models (GLM) with a binomial error distribution and a or boulders, were classified as crevices. We defined scree logit link function (logistic regression models). In order to deposits as accumulations of rock fragments at the base of estimated the availability of different roost types, we calculated cliffs, composed mainly of rocks about 10–80 cm in diameter. the relative surface of rocky areas and counted the number of Roosts in fissures of boulders within scree deposits were buildings in the 10-km-radius area. Land cover data used for considered as crevices. We characterised each roost using obtaining the variables for the habitat selection analysis and the the following variables: elevation, distance to the capture site relative rock cover were obtained from Corine Land Cover (capture distance) and elevation difference relative to the 2006 (http://sia.eionet.europa.eu/CLC2006), while the treeline in each area (treeline difference). We tested whether cartography of buildings was obtained from the Territorial data were normally distributed with the Shapiro-Wilk test and Information System of Aragón SITAR (http://sitar.aragon.es/) determined homogeneity of variances using Levene’s test. and the Cartographic Institute of Catalunya ICC (http://www. Parameters that fulfilled both assumptions were analysed icc.es/). Since availabilities of different roost types were not using one-way ANOVA (α=0.05), and the Tukey method comparable at the unit level—e.g. scree and rock walls vs. was used for post hoc multiple test comparisons. For param- buildings—their availability at different elevations was eters that did not fulfil the assumption of normality, we used assessed by probability density functions. We generated the nonparametric Kruskal-Wallis test and Wilcoxon signed kernel density estimations (KDE) of available buildings and rank test (for pairwise comparisons). rocky areas across the elevation range using the density func- We analysed eight habitat variables to test for habitat selec- tion available in R package STAT (Deng and Wickham 2011), tion and compared our results with the published literature. We and plotted with the KDE of the employed roosts to obtain a calculated the relative area of each habitat type in two visual reference of roost availability with respect to elevation. predefined radii around each roosting site: r=1,300 m to obtain Roost fidelity (FR) was calculated using the following comparable results with that of Rutishauser et al. (2012), and equation: r=2,900 m, which is the average distance recorded between the Xn capture sites and roosting sites in this study. The studied vari- Ri−1 F ¼ ables were the relative area in percentages of (1) deciduous R − i¼1 Pi 1 forest, (2) mixed forest, (3) coniferous forest, (4) open forest, (5) shrubbery, (6) orchards and (7) meadows. Following (Rutishauser et al. 2012), we also calculated the landscape diversity based on four landscape types (settlement, forest, where Ri is the number of different roosts used by the bat i, shrubbery and meadows). Correlation between variables was Pi is the number of records for the bat i,andn is the total Eur J Wildl Res

number of bats in the sample. FR, therefore, ranges from 0 to 1 1.41 km away from the closest forest and 349±297 m above and reflects the probability of roost switching each day, with the treeline. The area within the 10-km radius around roosting the highest values indicating high lability (1=switches every sites consisted of a landscape where the relative extent of bare day) and low values indicating high fidelity (0=same roost rock areas was 27.6 % and the average building availability everyday). All spatial and statistical analyses were performed was 1.67±1.35 building/km2. However, the availability of using GIS software ArcView 3.2 and R 2.9.2 (http://cran.r- both types of roosts varied with elevation (Fig. 3). Building project.org/). density peaked at 1,200 m amsl and tended to decrease with increasing elevation, even though buildings occurred at up to 2,500 m. The peak in crevice and scree resources was at 2,500 m, though rocky areas were available in the elevation Results range between 1,500 and 3,000 m.

We captured 147 bats at 16 netting sites, 117 of them (79 %) Spatial organisation being alpine long-eared bats (Table 1). We radio-tagged 51 animals and were able to identify the roosts of 37 (72 %): 8 We found no difference in the elevation of capture sites between breeding females, 12 nulliparous females and 17 males for an the three bat classes (Kruskal-Wallis: X2=1.77, df=2, p=0.410), average of 3.4±0.81 location points during the 8-day sam- but we did find differences in the elevation of roosting sites pling period. The total radio-tracking effort amounted to 178 (ANOVA: F=6.748, df=2, p=0.002). The average elevation of person-days. roosts used by breeding bats was lower than the elevation of nulliparous females (Tukey: p<0.01) and males (Tukey: p= Roost types 0.030) (Table 2). Despite the mean elevation of nulliparous females being 147 m higher than that of males, differences were We identified 54 roosts, averaging 2.2±0.85 roost per bat not statistical significance (Tukey: p=0.141). The overall mean (several tracked bats shared the same roosts). P. macrobullaris elevation of roosts and capture sites was not statistically different used three of the four defined roosts categories: crevices (n= (Wilcoxon test: v=823.5, p=0.488), and neither were differ- 30), scree deposits (21) and buildings (3). Roosts were located ences within breeding females (Wilcoxon test: v=38, p= between 1,450 and 2,430 m amsl. The crevices used by bats 0.070), nulliparous females (Wilcoxon test: v=20, p=0.15) were located in various types of rock structures. Bats used and males (Wilcoxon test: v=327, p=0.410). Elevation differed crevices on both sunny south faces and shaded north faces depending on the roost type used (ANOVA: F=4.716, df=2,p= with snowfields nearby (10–15 m). Males roosted in scree 0.013), as roosts located at rock crevices (1,997±255 m) were at deposits more often than females, yet five females were also a higher elevation than roosts in buildings (1,633±175 m, tracked to these locations, including a pregnant female found Tukey: p=0.035). No elevation differences were observed be- roosting in a scree deposit for a single day. At these deposits, tween crevices and screes (Tukey: p=0.089), and screes and bats were found alone under average-sized stones (Fig. 2c). buildings (Tukey: p=0.299). Crevice and scree roosts were The three building roosts (5.5 % of all roosts) housed mater- respectively 458±254 m and 254±287 m above the treeline, nity colonies comprising 10–15 individuals. The buildings while building roosts were 103±92 m below the treeline. were in relatively good condition, and the colonies were The overall index of roosting fidelity (FR) was 0.51, but located in narrow spaces between wall stones or in the rafters. values differed considerably among bat classes and roost The three buildings were solitary structures surrounded by categories. By class, pregnant and lactating females showed natural habitats (Table 2). the highest fidelity (FR=0.11), nulliparous females had inter- mediate values (FR=0.35), whereas males exhibited high Habitat selection and roost availability roosting lability (FR=0.88). By category, bats roosting in buildings had the highest fidelity (FR=0), followed by bats The chi-square goodness-of-fit analysis showed that roosts roosting in crevices (FR=0.21). Conversely, bats roosting in were not located randomly in relation to surrounding habitat scree deposits exhibited low fidelity, switching roosts every 2 types (X =64.422, df=9, p<0.001). The logistic regression day they were tracked (FR=1). models showed that roosting sites were located closer to meadows and open forest, and further away from deciduous forest and shrubbery (Table 3). The values of the remaining variables were not statistically significant. The two analysed Discussion ranges (r=1,300mandr=2,900 m) showed consistent results, though the effect of mixed forest was only significant in the This study shows that in the Pyrenees the use of alpine habitats 1,300-m radius. Roosts were located on average 1.91± by P. macrobullaris is not limited to commuting and Eur J Wildl Res

Table 1 General characteristics of capture locations and obtained samples. Numbers between parentheses indicate the number of radio-tracked individuals

Valley Place Elevation (m) Distance to forest (km) Breeding females Nulliparous females Males

Ansó Zuriza 1,550 0.62 1 (1) 4 2 (2) Tachera 1,920 1.31 0 2 (2) 0 Hecho Plan d’Aniz 1,740 1.44 4 (2) 5 2 (2) Aisa Cubilar de las Vacas 1,570 0.67 2 1 1 (1) Izagra 1,800 2.74 1 (1) 2 (2) 0 Tena La Ripera 1,590 1.3 2 (1) 5 (1) 1 (1) Ibon de Piedrafita 1,640 1.23 0 0 1 Llana del Portillo 1,790 3.7 0 2 (2) 2 (1) Cuello Bubalar 1,800 0.32 0 0 1 (1) Ordesa-Añisclo Pardina 1,900 1.72 0 2 (1) 5 (2) Cuello Bizeto 2,005 2.49 0 0 1 (1) Arrablo 2,350 3.86 5(2) 3(1) 4(1) Insolas 2,370 2.77 0 0 14 (3) Bielsa Barrosa 1,780 1.87 1 (1) 8 (1) 7 (3) Plan Biadós 1,770 0.27 5 (3) 6 (3) 4 (2) Pallars Sobirà Campirme 2,030 0.12 2 (2) 4 (4) 5 (1) Average Total 1,850±244 1.65±1.17 23 (13) 44 (17) 50 (21) occasional foraging bouts but instead this species also roosts nesting places for alpine birds such as the alpine chough, the and breeds in alpine environments. Eighty-five percent of the wallcreeper and the white-winged snowfinch (Madge and roosts we found were located above the treeline, including Burn 1994;Saniga1995; Yan-Hua et al. 2002). These sites most of the breeding sites. The ecological pattern of roost use likely provide protection from predators and harsh meteoro- by this species does not correspond to that of a lowland logical conditions. species that occasionally commutes to higher elevations for Notably, roosting among the small stones of scree deposits foraging. Instead, the majority of P. macrobullaris roosts was common in alpine long-eared bats. Some bats, mainly occur at the same elevations as foraging areas (Table 2), crevice-dwellers such as Myotis daubentonii and Myotis suggesting that the population of alpine long-eared bats is nattereri, have occasionally been found in rocky debris on resident in the Pyrenean alpine habitat (Fig. 2). Free-ranging the floor of caves and tunnels (Baagøe 2001). Furthermore, individuals have also been captured at high elevations (above there is a single observation of a northern bat ( 1,800 m) in the Alps, the Pindos Mountains, the Caucasus and nilsonii) roosting among stones in Norway (van der Kooij the Zagros Mountains (Alberdi et al. 2013), suggesting that 1999). Myotis leibii and Myotis evotis are, to our knowledge, the pattern we observed may be similar to that of other the only species known to commonly roost in talus slopes populations. (Solick and Barclay 2006; Johnson et al. 2011). Recently, Myotis lucifugus was recorded to roost in scree slopes in Roost types Colorado, USA (D. Neubaum, personal communication). Ta- lus slopes are typical roosting resources for several small P. macrobullaris used various structures including natural and mammals closely linked to rocky environments, such as the artificial shelters for roosting, as is common among bats snow vole (Chionomys nivalis) and the North American pika (Rancourt et al. 2005; Lausen and Barclay 2006). Neverthe- (Ochotona princeps) (Smith and Weston 1990), although less, the observed roosting behaviour differed from that de- these mammals usually build a lair below or among stones. scribed in previous studies of this species (Benda et al. 2004; Scree is abundant and easy to identify in craggy landscapes, Presetnik et al. 2009;Mattei-Roesli2010; Rutishauser et al. where it offers a variety of microclimatic conditions depend- 2012)andofPlecotus bats in general (Swift 1998). In our ing on composition, rock sizes, and deposit depth (Scapozza study area, alpine long-eared bats roosted primarily in crev- et al. 2011). Thus, bats can potentially find the optimal con- ices. We found that both males and females (including five of ditions under scree deposits by moving through the deposit. the nine pregnant and lactating bats) used crevices during the Only three breeding females out of the 37 tracked bats were active season. Crevices in cliffs are also typically used as observed roosting in buildings. This contrasts with data from Eur J Wildl Res

Fig. 2 Roost views, with icons showing exact roost locations. a General view of a roost area in Añisclo Canyon; the area covered by photos b and c is marked with white insets. b Detail of the limestone cliff with a horizontal crevice (1,880 m) where two breeding females roosted. c The scree deposit (2,140 m) of five roosting points belonging to two male bats; the area shown by photo d is marked with an inset. d A male alpine long-eared bat roosting in a scree deposit sticking out its head after stones had been removed

the Alps, where nearly all known roosts are exclusively locat- building surveys considered suitable a priori, which entails a ed in buildings (Presetnik et al. 2009;Mattei-Roesli2010; bias towards buildings. Similarly, the few roosts that were Rutishauser et al. 2012). P. macrobullaris in the Alps and the previously known in the Pyrenees were also in buildings Pyrenees may indeed have completely different roosting be- (Dejean 2009, personal observations), but our radio-tracking haviours; however, we cannot exclude the possibility that approach revealed an entirely different scenario. Because studies in the Alps may have overemphasised the importance P. macrobullaris has also been captured in supraforestal hab- of buildings. Almost all the records in the Alps come from itats in the Alps (Alberdi et al. 2013), a similar radio-tracking

Table 2 Summary statistics for roosting sites of breeding females, nulliparous females and males. The last three columns show the number of roost types used by bats from each category

Capture elevation (m) Roosting Treeline Forest distance (km) Capture distance (km) Crevices Screes Buildings elevation (m) difference (m)

Breeding 1,887±225 1,705±208 123±280 0.78±1.02 2.86±2.17 5 1 3 females Nulliparous 1,921±118 2,071±212 510±255 2.74±1.22 3.51±2.39 8 4 0 females Males 1,930±291 1,924±234 345±285 1.89±1.37 2.66±2.13 17 16 0 Total 1,850±244 1,921±249 349±297 1.91±1.41 2.88±2.18 30 21 3 Eur J Wildl Res

Table 3 Used and available habitat features and the coefficients of the GLM in the two analysed scales

1300 m radius 2900 m radius

Used Available Coefficient Used Available Coefficient

Deciduous forest (%) 2.57±5.62 16.10±20.55 −0.087*** 3.68±5.21 15.77±16.88 −0.092*** Mixed forest (%) 0.51±1.89 5.93±13.56 −0.125* 2.03±4.83 5.76±10.29 −0.023 Coniferous forest (%) 8.61±16.67 14.70±19.83 −0.014 7.35±11.47 14.69±15.85 −0.023 Open forest (%) 11.01±13.40 8.12±12.98 0.033** 7.50±9.39 7.94±9.82 0.061*** Shrubbery (%) 1.25±3.77 8.03±13.55 −0.124** 2.18±2.87 7.57±9.94 −0.109** Orchards (%) 0 0.04±0.75 −9.461 0 0.04±0.47 −12.906 Meadows (%) 50.59±18.58 22.66±23.45 0.023*** 51.33±13.33 22.54±19.63 0.045*** Richness (1–4) 2.27±0.87 2.37±0.69 0.106 2.81±0.39 2.97±0.62 −0.474

*p<0.05; **p<0.01; ***p<0.001 (significant) study in the Alps would unambiguously determine whether gradient (Fig. 3). Most buildings are located below the treeline the observations we made in the Pyrenees can be extrapolated while most rock areas can be found in the alpine belt. Bats to other areas. opted not to fly to lower elevations for roosting, and the radio- tracking approach disclosed that more breeding females Roost availability and habitat selection roosted in crevices than in buildings, some of which were located above the treeline. Additionally, all non-breeding bats Results from the habitat selection analysis suggest that at least were found to use crevices in rocky structures. This suggests in the Pyrenees P. macrobullaris is an open-space forager. that females may select artificial shelters either when suitable These results are in accordance with the molecular diet anal- rock resources in the surroundings of foraging grounds are ysis, which showed that bats forage in alpine meadows limited or when they provide more suitable, perhaps warmer (Alberdi et al. 2012b). Additionally, no P. macrobullaris have or drier, conditions for reproduction than rocks. been captured so far in dense forest areas in the Pyrenees The pattern identified in this study largely contrasts with (Alberdi et al. 2013). Roosting near foraging areas would the observations reported from the Alps, where roosting areas allow bats to save energy by minimising long displacement of P. macrobullaris were linked to deciduous forest environ- flights, and the predominant use of crevices and scree deposits ments, while meadows were avoided (Rutishauser et al. is probably linked to that fact, since natural rock resources in 2012). It is important to note that another radio-tracking study the alpine belt provide almost unlimited roosts near the carried out in the Alps concluded that bats avoided woodlands meadows used as foraging grounds. Rock roosts were located (Preatoni et al. 2011). Therefore, further studies are necessary on average at higher elevation than roost in buildings, corre- in order to obtain a clearer picture of the actual ecological sponding to their relative availability across the elevational preferences of this species in the Alps.

Fig. 3 Density plot of the elevational distribution of used roosts and the availability of different roosting resources across the altitudinal gradient. The grey area indicates the kernel density estimation (KDE) of roosting sites. The blue line indicates the KDE of buildings. The red line indicates the KDE of the rock Density resources. The vertical dashed line indicates the average treeline elevation in the study area 0.0000 0.0005 0.0010 0.0015 500 1000 1500 2000 2500 3000 Elevation range Eur J Wildl Res

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