Diet of Hoary (Lasiurus Cinereus) and Silver-Haired (Lasionycteris Noctivagans) Bats While Migrating through Southwestern Alberta in Late Summer and Autumn
Reimer, Jesika P., Baerwald, Erin F., Barclay, Robert M. R., The American Midland Naturalist
The feeding habits of hoary (Lasiurus cinereus) and silver-haired (Lasionycteris noctivagans) bats have been documented for their summer grounds, but little is known about their feeding habits while en route during migration. We analyzed stomach contents of L. cinereus and L. noctivagans collected at a wind-turbine facility in southwestern Alberta to gain insight into the feeding behavior of migrating bats. We addressed four questions: (1) Do L. cinereus and L. noctivagans feed while en route? (2) On what prey types do each species feed? (3) Do diets differ between species? (4) Do diets differ between age classes within each species? We found that both species fed while migrating and that their diets were similar to those found in their summer grounds, with the exception that L. cinereus consumed a considerable number of water boatmen (Hemiptera; Corixidae). Diets differed between species and age groups within species.
Of the bats in North America, perhaps the least well studied are those that migrate long distances, such as hoary (Lasiurus dnereus), eastern red (L. borealis) and silver-haired bats (Lasionycteris noctivagans). For example, previous studies have described the feeding habits of hoary and silver-haired bats in their summer range (e.g., Ross, 1967; Black, 1974; Whitaker et al, 1977, 1981; Kunz, 1982; Barclay, 1985, 1986), yet little is known about their feeding behavior during migration. While previous studies have included data-collection periods that overlapped with the autumn migration season, no distinction was made between migrating individuals and summer residents.
The diet of insectivorous bats is influenced by their morphology, echolocation calls and foraging habitat and, thus, varies among species (e.g., Barclay, 1985; Bogdanowicz et al., 1999). Lasiurus cinereus is relatively large (adult body mass 25-30 g; van ZyIl dejong, 1985), with a high wing loading and aspect ratio that allow individuals straight, fast, efficient flight necessary for migration. However, these traits also limit the available foraging habitat to less cluttered areas (Barclay, 1985, 1986). The echolocation calls of L. cinereus are intense, and of relatively low frequency, allowing for prey detection over longer distances (Simmons and Stein, 1980; Barclay, 1986; Neuweiler, 1989). In their summer ranges, L. cinereus feed on large insects such as Lepidoptera, Coleóptera and Odonata (Ross, 1961; Black, 1974; Barclay, 1985), as well as Hymenoptera and Diptera (Ross, 1961; Whitaker et al, 1977; Barclay, 1985; Rolseth et al, 1994). Diet composition changes with age in juveniles during the first few weeks after fledging (Rolseth et al, 1994). Recentiy, Valdez and Cryan (2009) reported that in spring, migrating hoary bats in New Mexico feed almost exclusively on moths,
Lasionycteris noctivagans has intermediate wing loading associated with its smaller size (1215 g), which allows for relatively slow maneuverable flight. Foraging is typically in or near forested areas (Kunz, 1982). They have broadband echolocation calls allowing for shorter range but more detailed prey detection compared to the low, constant frequency calls of Lasiurus cinereas (Barclay, 1986). The calls, and the reduced size and increased maneuverability of L. noctivagans, allows individuals to capture a wider range of smaller prey compared to L. anereus (Barclay, 1985, 1986). In their summer grounds, L. noctivagans, feed extensively on Lepidoptera and Diptera, as well as on Homoptera, Hemiptera, Hymenoptera, Coleoptera and Neuroptera (Black, 1974; Whitaker et al., 1981; Barclay, 1985).
Lasiurus anereus and Lasionycteris noctivagans frequently are killed at wind turbines during late summer and autumn migration (Johnson et al, 2004; Arnett et al, 2008; Baerwald, 2008) . One of the hypotheses to explain such fatalities is that these bats are attracted to and feed on insects around the turbines (Kunz et al, 2007; Cryan and Barclay, 2009). …