Absorption of visible spectrum radiation by the wing membranes of living pteropodid bats.
The wing membranes of bats present a large surface area upon which radiation might be taken up, increasing heat load to the animals. This, combined with the high amount of heat produced during flight, has been advanced as one hypothesis explaining the fact that bats are almost exclusively nocturnal. The proportion of short-wave (visible) radiation absorbed by bat wing membrane has previously been measured at between 0.7 and 0.92. These measurements were made on pieces of membrane taken from the wings of dead, mainly insectivorous bats from temperate regions. Here we examined the amount of light transmitted through and reflected off the wing membranes of four species of live pteropodid bats. There were significant differences in wing reflection between species. At 0.68, the average proportion of light absorbed into the wing membranes was lower than previously reported. This might be because we worked with live animals or because ours were tropical bats which are routinely exposed to tropical sun when roosting. Variation in wing tension strongly affected light absorption. It was predicted that the relaxed state of wing membrane through part of the wing beat cycle would increase the absorption of light into the wings of day-flying bats. The proportion of light absorbed into wings was shown to be an important factor in the heat balance of hypothetical bats flying during the day. Our results raise the predicted temperature at which bats flying during the day might experience hyperthermia by approximately 2 degrees C and suggest that variation in albedo of wings between species may make some species more susceptible to overheating than others.
Thomson
S C
SC
Aberdeen Centre for Energy Regulation and Obesity, Department of Zoology, University of Aberdeen, UK. j.speakman@aberdeen.ac.uk
Speakman
J R
JR
D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D001833:Body Temperature Regulation / Q000502:physiology*; D002685:Chiroptera / Q000502:physiology*; D002980:Climate; D003116:Color; D005260:Female; D005426:Flight, Animal / Q000502:physiology; D006358:Hot Temperature; D008027:Light; D008297:Male; D012879:Skin Physiological Phenomena; D013472:Sunlight; D014921:Wings, Animal / Q000502:physiology* / Q000528:radiation effects