1. 1.|Independent of their diverse feeding habits almost all bats are nocturnal. One hypothesis for chiropteran nocturnality is that bats flying in the day experience fatal hyperthermia because their wings take up significant amounts of short-wave radiation which they are unable to dissipate convectively. Factors that will critically affect a bat's susceptibility to overheating are the albedo and transmittance of wing membranes to short-wave radiation. 2. 2.|Albedo of taut segments of bat wings from four species of insectivorous bats and one Pteropid varied between 0.026 (for Rhinolophus hipposideros) and 0.069 (Plecotus auritus). 3. 3.|Transmittance exceeded albedo in all species studied and varied from 0.077 (Pipistrellus pipistrellus) to 0.194 (P. auritus). In this small sample there was no relationship between albedo and transmittance. 4. 4.|Total absorbed short-wave radiation amounted to between 70 and 92% of the incident radiation, and averaged 81.9% (SE = 2.4%, n = 9). Given a clear sky short-wave flux density of about 971 W · m-2 a typical small insectivorous bat (5g, wing area = 0.013 m2, absorptivity = 81.9%) with fully outstretched wings and the sun directly overhead would absorb about 10.65 W, compared with the maximum endogenous heat production from flight of 0.83 W. 5. 5.|Predicted maximum exogenous heat load relative to maximum endogenous heat load declined as a function of body mass, however, even in the largest known bats (1.4 kg) the exogenous burden exceeded by a factor of 3 the endogenous heat load.
- energy balance
- flight cost