J. Zool., Lond. (2000) 252,11±17 # 2000 The Zoological Society of London Printed in the United Kingdom Social and population structure of a gleaning bat, Plecotus auritus A. C. Entwistle*, P. A. Racey and J. R. Speakman Department of Zoology, University of Aberdeen, Aberdeen AB24 2TZ, U.K. (Accepted 21 September 1999) Abstract Brown long-eared bats Plecotus auritus occupying 30 summer roosts in north-east Scotland were studied over 15 years. During this time 1365 bats were ringed, and a further 720 recaptures were made. Individual bats showed a high degree of roost ®delity, returning to one main roost site; < 1% of recaptured bats had moved among roost sites, and all recorded movements (n = 5) were < 300 m. Adults of both sexes were loyal to the roost sites at which they were ®rst captured, indicating long-term use of roosts. At least some juveniles (n = 32) of both sexes returned to the natal roost. Mark±recapture estimates indicated that colonies of this species were substantially larger (c. 30±50 individuals) than assumed in previous studies. Plecotus auritus differs from most other temperate zone, vespertilionid species in that there was no evidence of sexual segregation during summer, with males present in all colonies throughout the period of occupancy. Population structure in summer seems to be consistent with a metapopulation model, with discrete sub-populations showing minimal interchange. The group size, colony composition and population structure described in this species may be associated with the wing shape (particularly aspect ratio) and foraging behaviour of P. auritus. It is postulated that relative motility, linked to wing structure, may affect the distribution of individuals, and may have implications for the genetic structure of this species. Correlations between aspect ratio and both colony size and migratory behaviour, across British bat species, indicate that wing shape could be an important factor contributing to patterns of social behaviour and genetic structuring in bats. Key words: Chiroptera, social structure, metapopulation, wing morphology, philopatry INTRODUCTION of morphological and ecological specializations. However, surprisingly little information is available The autecology of a species underlies the distribution of about the patterns and variation in dispersal behaviour individuals, their use of space and resources, interplay and social organization of many, even common, bat with conspeci®cs, and consequently population struc- species. In addition, few attempts have been made to ture. The relationship between ecology and social explain distributions and determine the population behaviour within species has been the source of con- structure of these mammals, and to explain how siderable study, particularly with respect to the such variation may relate to morphological factors or formation of groups (Alexander, 1974; Wilson, 1975). ecological specializations. Studies of variation in wing However, it often remains unclear how speci®c eco- morphology have shown it to be closely associated with logical and morphological specializations may affect feeding specializations and community structuring group formation and population structure. (Fenton, 1972; Aldridge & Rautenbach, 1987; Findley, In general, the social and population structure of bats 1993). Furthermore, a relationship between wing shape is not well known. Most of our knowledge of vespertil- (aspect ratio) and foraging range (Jones, Duverge & ionid behaviour is based upon a few well-studied species Ransome, 1995) leads to a prediction that wing such as Pipistrellus pipistrellus and Myotis lucifugus. morphology may affect the dispersal abilities of bats, Overall, the family is ecologically and behaviourally with implications for group formation and distribution diverse (Bradbury, 1977; Kunz, 1982), with a wide range of individual species. It is predicted that wing morphology may have further implications for both social and population structure. *All correspondence to: Dr Abigail Entwistle, Fauna & Flora International, Great Eastern House, Tenison Road, Cambridge In this paper we examine population structure, group CB1 2DT, U.K. E-mail: [email protected] size and composition in the brown long-eared bat 12 A. C. Entwistle, P. A. Racey and J. R. Speakman Plecotus auritus, L., which differs in both morphology Assessment of colony size and feeding behaviour from most other vespertilionid bat species. This species displays related morphological Previous attempts at determining colony size from and ecological specializations: distinctive short broad emergence counts for this species proved unsuccessful wings and long ears, coupled with low intensity echo- given the low light intensity at the time of emergence. location calls, used to glean prey (predominantly moths) Instead, the number of bats using each roost was directly from foliage (Anderson & Racey, 1991). Flight assessed in 3 ways: is slow, but manoeuvrable, as a result of low wing (1) An average of the number of bats seen in the attic aspect ratio and low wing loading (Norberg, 1976). The on different visits (average colony count), which is relatively short foraging range described in P. auritus comparable between roosts and independent of effort. (Entwistle, Racey & Speakman, 1996) is consistent with (2) The `minimum number alive' (MNA) (Krebs, 1989) lower ranges associated with species with such wing in a given year was calculated from ringing records, and morphology (Jones et al., 1995). In Britain P. auritus can be considered as the lower limit of population size roosts mostly within the attics of houses, which appear (Montgomery, 1987). to be selected on the basis of a suite of characteristics, (3) The Jolly±Seber method (Seber, 1982) was used to including woodland availability, attic structure and provide an upper population estimate which includes an temperature (Entwistle et al., 1997). However, there is estimate of the individuals that might have evaded surprisingly little detailed information about the occu- capture. In this study all assumptions inherent in the pancy of roost sites by this species, social organization Jolly±Seber method were considered to be ful®lled (see of colonies or population structure (but see Burland also Boyd & Stebbings, 1989). et al., in press). The present study examines several components of social organization and population structure in this Interspeci®c comparisons of wing morphology and species. Furthermore, since P. auritus has an unusual behaviour wing morphology (Norberg, 1976), it provides a useful model to examine how morphology and ecological Relationships between wing morphology and both specializations may be linked to social behaviour and colony size and migratory abilities, for British bat population structure. species, were examined using stepwise regressions. Data were collated on maximum colony sizes from the available literature (Greenaway & Hutson, 1990; MATERIALS AND METHODS Nowak, 1994). Classi®cations of migratory and sedentary species among European bats were taken from A ringing programme was conducted in north-east Strelkov (1969). Interspeci®c comparisons were made Scotland between 1978 and 1989, under licence from the between these data and corresponding measures of statutory nature conservation authorities. Between 1991 morphology (mass, wingspan, ear length, aspect ratio and 1993 this study was extended with a more intensive and wing loading) for each species (from Norberg & ringing schedule, when roosts were checked up to 5 Rayner, 1987). times each summer (mean number of visits = 2.2 per roost each year). Efforts were made to identify all roosts in the study area (an area c. 50 by 20 km), and localities RESULTS with a high concentration of roosts were intensively surveyed, so that all extant roosts could be identi®ed. A Roost occupancy total of 30 roosts in buildings was studied, and the distance between these structures ranged from 100 m to All captures took place between April and October, 40 km, although 8 roosts were located within 4 km of with few individuals found after the beginning of each other. October (average = 5 individuals). Across all 30 roosts, Bats were caught either by hand or with a hand net. bats were present on 65% of visits between 1991 and The total number of bats counted on each visit was 1993 (n = 195). The likelihood of bats being located was recorded, including those that were seen but could not not related to the number of visits made to the roost 2 be captured. Information collected from each individual (F1,11 = 0.03, r < 0.01, n = 12, NS). Bats frequently captured included: sex, adult or juvenile (based upon changed roosting position within the roost site through the epiphyseal gap; Anthony, 1988), and reproductive the course of the summer, although movements maturity and status (Racey, 1974; Entwistle et al., appeared unrelated to the timings of capture. 1998). Bats were marked using 3.0 mm (closed internal diameter) aluminium rings (Mammal Society, London), bearing an individual code. A small proportion of bats Ringing and site ®delity (n = 68) were double ringed to assess ring loss (estimated as < 3%). Juveniles were not ringed until the epiphyses Between 1978 and 1993, 2206 bats were caught. Of had fused, and overall there was minimal incidence of these, 1365 bats were ®rst captures which were subse- damage to bats from the rings. quently ringed, 121 were released without ringing and Social structure in the brown long-eared bat 13 Table 1. The numbers of recaptures made after