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Colonies and reproductive patterns of tree-roosting female eastern pipistrelle bats in Indiana.

Article Excerpt
ABSTRACT. We investigated colonies and reproductive patterns of adult female eastern pipistrelles, Pipistrellus subflavus, in Indiana during the non-hibernation season in 1999-2000. Females began to form small colonies (range, 1-8 individuals) during early May, and parturition occurred during late June and early July (sex ratio of young = 1:1). Young pipistrelles began to fly during middle to late July. Colonies of adult females began to disband soon after the young became volant. Alter leaving colonies, the adult females roosted singly tier the remainder of the summer, and then moved to hibernation sites from late August through September. This study is the first detailed description of tree colonies and reproductive patterns of eastern pipistrelles roosting in natural structures.

Keywords: Bats, eastern pipistrelle, Pipistrellus subflavus, colonies, reproduction, tree roosts

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Eastern pipistrelles are common across the mid-western United States (Barbour & Davis 1969), and in summer prefer wooded habitats near permanent water sources such as streams and ponds (Mumford & Whitaker 1982). The eastern pipistrelle is usually a tree-roosting species, spending the day in clusters of dead or live foliage (Veilleux et al. 2003). Although eastern pipistrelles roost mainly in tree foliage, they sometimes roost in buildings; and to date studies investigating populations and reproduction of eastern pipistrelles in summer are based solely on colonies located in manmade structures (Allen 1921; Cope et al. 1961; Jones & Pagels 1968; Jones & Suttkus 1973; Whitaker 1998; Winchell & Kunz 1996). In this study we examined colonial behavior and reproductive patterns of eastern pipistrelles roosting in trees.

Female eastern pipistrelles leave hibernacula during April through mid-May (Whitaker & Rissler 1992), presumably migrate a relatively short distance (perhaps 50-100 km), and then begin to form summer colonies (Hoying & Kunz 1998; Whitaker 1998). After a gestation period of approximately 44 days (Wimsatt 1945) females give birth to two young (Lane 1946; Whitaker 1998; Wimsatt 1945) in late June to early July (Hoying 1983; Whitaker 1998). However, parturition may occur as early as late May at more southern latitudes (Jennings 1958). In many litters only one pup survives due to predation (Hoying & Kunz 1998) or other unknown factors. Young fly when approximately three weeks old and are able to effectively forage about one week later (Fujita & Kunz 1984). Adults leave the maternity roost once the young are fully weaned (Hoying 1983; Whitaker 1998), although the young may remain in the roost for longer periods. Whitaker (1998) reported mean summer colony size in man-made roosts to be 15 individuals (range 7-29), and Hoying & Kunz (1998) report the largest summer colony on record at approximately 55 bats.

The purpose of our study was to investigate colonial behavior (arrival at summering grounds, colony size and fluctuations, summer colony breakdown, migration to hibernacula following the summer roosting season) and describe reproduction events (dates of pregnancy and parturition for adult females, and first flight and weaning of young) for eastern pipistrelles roosting in trees. We also compare these data with similar data from pipistrelle colonies located in buildings.

METHODS

Data were collected mainly during April through September 1999 and 2000 at Prairie Creek in southwest Vigo County, in southwest Indiana (UTM 43.48.000N, 4.54.000E), although information from several mist-netting samples collected during 1997 and 1998 also is included (see Veilleux et al. 2003 for details of habitat and netting areas). Mist-netting and radio-telemetry were used to gather data on dates of arrival and departure from summering grounds, dates and duration of female reproductive stages (i.e.,...

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