Our results showed that Black-nest Swiftlets appeared to specialize solely on larger-bodied
hymenoptera (89% of all food items taken, of which 97% were flying ants). The low diversity of species in the bolus suggests that the majority were taken from swarms. I t is unlikely that this represents a sampling bias due to timing of feeding, because both Black-nest and White-nest Swiftlets were caught at the same time on the same day, and the latter did not show a similar
preponderance of ants in their boluses. This foraging strategy may be related to the larger body size of the Black-nest Swiftlet (40-2000/0 larger than the other Malaysian species) and its consequent potential reduction in manoeuvrability, resulting, for example, in
being unable to chase individual prey. Manoeuvrability has been shown to be important in determining foraging patterns and diet in bats (Aldridge & Rautenbach 1987). Furthermore, Waugh and Hails (1983) state, of C. esculenta, that 'their lighter body weight relative to tail and wing length are likely to confer greater manoeuvrability permitting capture of
faster turning insects, particularly near vegetation', which implies that the opposite may be true for the larger, heavier-bodied Black-nest Swiftlets.