ROOSTS OF INDIANA BATS (MYOTIS SODALIS) NEAR THE INDIANAPOLIS INTERNATIONAL AIRPORT (1997-2001)

Long-term roosting ecology of the federally-endangered Indiana myotis (Myotis sodalis), in a rapidly-developing area immediately southwest of the Indianapolis International Airport was examined. A dead shagbark hickory, Carya ovata, in a woodlot 1 km S of Interstate Highway 70 was the most utilized roost tree throughout the study, from 1996 to the winter of 2001-02 when it fell. Bats arrived at this roost in April and regularly used it until October of most years, with young fledging in July. Based on consistent increases in the maximum number of bats seen exiting this roost during 1997-1999, this colony was growing. At least four other primary roosts, all cottonwoods (Populus de/toides), and 24 alternate roosts were used at this site. Movement patterns among and between these roosts indicate that all bats belong to one colony spread across a fairly large area. The Indiana myotis (Myotis soda/is) is the most intensively studied of all tree-roosting bats, in terms of both the number of roosts that have been identified and the amount of published literature (Kurta 2005; Barclay & Kurta 2007). Despite protection of multiple high priority hibernacula and intense study of the summer needs of this bat, the species continues to decline; and the reason(s) for this decline remains poorly understood (Clawson 2005) A typical primary maternity roost tree of this species consists of a fairly large tree (usually over 20 inches dbh) with sloughing bark that is open to the sun. Some of the initial observa­ tions of summer roosts by Indiana myotis suggest these bats make use of both primary and alternate roosts (Humphrey et al. 1977) with primary roosts receiving extensive use throughout summer. Later observations (Cal­ lahan et al. 1997) supported and further refined these observations. A maternity colony of Indiana myotis may include up to three primary roosts and many alternate roosts. Most of these previous studies often were concluded within two years, and particular colonies were studied (particularly by consul­ tants) for only a few days or weeks. The presence of long-term data has led us to further refine the traditional definitions of primary and alternate roost as follows. A primary Class I roost was used regularly by a large number of bats over extended periods of time and usually over more than one year. A primary Class II roost was used sometimes by large numbers of bats, but over shorter periods. Traditionally, a secondary or alternate roost has been consid­ ered to be a tree used by small numbers of bats over short periods of time (Callahan et al. 1997). However, we also recognized two classes of alternate roosts. An alternate Class I roost contained a large proportion of the colony for a short period of time, whereas an alternate Class II roost was used by only a few (often one) individuals. Some trees that we recognized as alternate Class I roosts would have been considered primary roosts by some authors (Callahan et al. 1997; Gardner et al. 1996) examining them only over short periods of time. Because these trees are used for relatively short periods of time, we suspect that they are actually roosts that bats roosted in, but found unsatisfactory.