Academic journal article The American Midland Naturalist

Intra-Annual and Interannual Fidelity to Summer Roost Areas by Female Eastern Pipistrelles, Pipistrellus Subflavus

Academic journal article The American Midland Naturalist

Intra-Annual and Interannual Fidelity to Summer Roost Areas by Female Eastern Pipistrelles, Pipistrellus Subflavus

Article excerpt

ABSTRACT.-

Bats in forests have strict roosting habitat requirements. The current paradigm in bat conservation has been to identify the specific characteristics of individual roost trees that arc selected by bats. Although this strategy is both practical and useful, it is also important to recognize landscape level interactions between bats and their roost habitats. Few studies have documented fidelity patterns of individual bats to specific roost habitat areas both within and between years. If bats are faithful to roost areas, conservation and management practices must incorporate the identification of the minimum size of areas required by bats during the summer season. We provide evidence that female eastern pipistrelles are faithful to small roost areas both within and between years, and that juvenile females exhibit female natal philopatry.

INTRODUCTION

Fidelity, in terms of roosting ecology of bats, is defined as the degree of faithfulness that an individual bat or bat colony shows to its roost (for review see Lewis, 1995; Kunz and Lumsden, 2003). The 'roost' may take various forms, including both summer roost sites and winter hibernacula. During summer, most bat species occurring in the temperate United States rear their young in maternity roosts. These roosts are variable in type, being located in man made (e.g., attics, barns) or natural structures (e.g., trees, caves) (for review see Kunz and Lumsden, 2003). Fidelity to a roost structure is also variable, with species exhibiting relatively high fidelity to stable rare roosts (e.g., caves) and low fidelity to unstable ubiquitous roosts (e.g., foliage; Lewis, 1995).

Recent research has described fidelity patterns for a number of species, especially those occurring in temperate North America (e.g., Lewis, 1996; Whilaker, 1998; Foster and Kurta, 1999). The majority of species, particularly those that form maternity colonies in trees, require a relatively large number of roost trees during a single season. Since females of most North American species give birth and rear young within maternity roosts, these studies are important from a conservation standpoint because they reveal the minimum habitat requirements necessary to sustain bat populations.

However, in addition to describing fidelity patterns of bats to a specific roost, it is important to document whether individuals exhibit fidelity to the same habitat area during a single summer season, as well as across multiple years. Fidelity to roost areas may result in fitness benefits, particularly for individuals of colonial species. Coloniality may benefit individual foraging success by facilitating information transfer about prey rich patches (Wilkinson, 1992; but see Kerth et al, 2001). In addition, roost microclimate is influenced by colony size (Kurta, 1985; Kurta and Kunz, 1988) and membership in a social group may allow individual bats, particularly reproductive females, to take advantage of energetically favorable conditions. Fidelity to relatively small habitat areas should facilitate group cohesion by increasing the probability of locating colony mates after foraging bouts and after returning to summer habitats following hibernation.

If individuals remain in and return to specific habitat areas within and between years, commercial and private development of natural areas pose serious problems for bats, as individuals may be displaced from areas that have been used as roost habitat for relatively long periods of time (Cryan et al, 2001). Costs associated with displacement may include the energetic cost of searching for new roost sites, disruption of social bonds among colony members and increased risk of predation as individuals move through unfamiliar areas. Unfortunately, few data are currently available that describe interannual and intra-annual fidelity to a roost habitat area by individual bats. The purpose of this paper is to report evidence that individual female eastern pipistrelles remain in relatively small roost habitat areas during a single summer and return to the same roost habitat area across successive years. …

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