Dietary Benefits of Twilight Foraging by the Insectivorous Bat Hipposideros speoris1

Abstract

Although bats are nocturnal, many species emerge from roosts to forage during twilight, despite a presumed high risk of predation at this time. Here, we describe twilight foraging by a maternity colony of Schneider's leafnosed bat (Hipposideros speoris) in the dry zone of Sri Lanka and determine the dietary benefits of such behavior. Bats usually began foraging during dusk, sometimes before sunset, and also foraged during twilight in the morning. Mean use of available twilight by four radio-tagged bats was 75 percent. Twilight foraging made up, on average, 47 percent of the total foraging time of these bats (range = 25-96%), although twilight consisted of only 12 percent of the available time between sunset and sunrise the next morning. Eight species of potential predators (7 birds and 1 mammal) were observed within a 1 km radius of the colony, of which 5 species are predicted to regularly capture bats. Bats took a wide diversity of prey (1 1 insect orders, including at least 27 families, and spiders) that ranged in wing length from 2.0 to 54.0 mm. Major orders in the diet were Coleoptera, Lepidoptera, and Diptera. Prey of secondary importance included Hemiptera, Hymenoptera, Isoptera, and Neuroptera. Bats captured large numbers of insects that were only available or had marked peaks in abundance during twilight. These groups included small, swarming insects (especially flies) that have peaks in flight activity at dusk and dawn, large diurnal species (especially dragonflies) that have crepuscular activity, and winged termites that emerge in swarms at dusk. Access to these insects was a clear benefit of twilight foraging.'

Partitioning of Time as an Ecological Resource

“…Although bats are nocturnal, many species emerge from roosts to forage during twilight. Field research on foraging by a maternity colony of Schneider's leafnosed bats (Hipposideros speoris) in Sri Lanka suggested that bats captured large numbers of insects that were only available or had marked peaks in abundance during twilight (Pavey et al 2001).…”

Mosquito Consumption by Insectivorous Bats: Does Size Matter?

“…Though bats of various sizes (small to large) have been observed consuming mosquitoes [7,8] and mosquitoes have been identified in the stomach contents of bats [9,10] as well as in bat feces [8,11,12], many dietary studies have found mosquitoes to represent only a small proportion of bat diet, with other groups (e.g., moths and beetles) more common in bat diets [13]. However, the importance of mosquitoes and other small, soft-bodied prey may be understated due to the greater susceptibility of soft-bodied prey to the processes involved in mastication and digestion [14,15] and the bias associated with techniques available to study bat diet [14,16] .…”

Effects of agroecosystems on insect and insectivorous bat activity:a preliminary finding based on light trap and mist net captures

“…Other studies have also documented the linkage between insect and bat abundance (Rautenbach et al, 1996;Pavey et al, 2001), as insects constitute the principal food component of insectivorous bats (Williams and Singh, 1951;Holyoak, 2001). Furthermore, food preference, availability, and accessibility of prey (Kusch et al, 2004;Almenar et al, 2012) could have resulted in the differences in agroecosystems' ability to support insectivorous bats.…”

“…Nearly all insectfeeding bats are nocturnal (Speakman, 1995), occupy a diversity of habitat types, and exploit a wide variety of prey (Altringham, 1996;Kalko et al, 1996). Some authors have suggested that insect prey abundance influences the local occurrence of insectivorous bats (Rautenbach et al, 1996;Pavey et al, 2001). In other words, changes in the activity level of insects may influence the foraging behavior and activity levels of the bats.…”