Activity Patterns, Habitat Use, and Prey Selection by Some African Insectivorous Bats

Abstract

Between 10 January and 14 February 1976, activity patterns, habitat use, and selection of prey by some insectivorous bats were studied in mopane and brachystegia deciduous woodlands in the Sengwa Wild Life Research Area of the Hostes Nicolle Institute of Wild Life Research in Rhodesia (18?10' S, 23013' E), using ultrasonic (=bat) detectors, light tags, and analysis of insect remains from bat feces. Some bats were active throughout the night, in part feeding, but in general bat activity was reduced from around midnight until just before dawn. Rain tended to suppress bat activity, although the timing of the rain was important. Since insects remained active in the rain, we suspect that the responses of the bats to rain reflected problems of thermoregulation associated with wet fur, and the effect of multiple echoes and attenuation of high-frequency sound on echolocation. Bright moonlight suppressed bat activity and altered the foraging patterns of light-tagged Scotophilus viridis, Eptesicus capensis, and Nycticeius schlieffeni which on dark nights fed above the canopy and along the grassland sides of meadow/woodland interfaces, but which were mainly restricted within the woodland on bright moonlight nights. Since a pair of bat hawks (Macheiramphus alcinus) nested near the study area and fed mainly on bats, we suggest that the bats' responses to moonlight are predator-avoidance behaviors. S. viridis (15 20 g), E. capensis (5 6 g), and N. schlieffeni (5 6 g) appeared to feed on concentrations of insects, and responded quickly to aggregations of insects around lights. These bats fed mainly on beetles (S. viridis-85%%; E. capensis-68%; N. schlieffeni-72%), although E. capensis also took moths (18.5%) and N. schlieffeni took flies (19%). Other insectivorous bats in the study area fed mainly on moths (Hipposideros caffer, Laephotis angolensis, Ga4uconycteris variegata) or beetles (Scotophilus nigrita), or both (Rhinolophus hildebrandti, Pipistrellus nanus). Data for some insectivorous bats from the vicinity of Salisbury, Rhodesia, indicated a similar separation for some bats (moths-Nycteris thebaica, Rhinolophus landeri; beetles-Rhinolopus clivosus) in addition to two species of Miniopterus which took mainly aquatic Diptera. The data from this study, with those from other works, are used to illustrate partitioning of insect prey by the species of bats known to occur in the Sengwa Wild Life Research Area. KNOWLEDGE OF THE PARTITIONING of available resources is central to the understanding of the ecological interactions between sympatric species of animals. While substantial data are available for some birds, in terms of what food is consumed and where (e.g, MacArthur 1958, Lack 1966. Keast 1968). this information is not available for most bats. There are reports of the insects eaten by different bats (e.g.. Ross 1967; Black 1972, 1974; Whitaker and Black 1976), but these are usually based on analysis of stomach contents or feces, and do not indicate where the bats had been feeding. Other studies (e.g., Kunz 1973) have shown that different insectivorous bats have different periods of activity that may be related