Transient Behavior, Nocturnal Activity Patterns, and Feeding Efficiency of Vampire Bats (Desmodus Rotundus) under Natural Conditions

During 5 netting nights, 99 vampire bats (Desmodus rotundus) (37 males, 57 females, five sex unrecorded) were taken in a mist net stretched before the entrance of a permanent cave roost in Tabasco. Each was banded; weight, sex, time of capture, and direction of passage (in or out of the roost) were noted; and the bat was then released. Because 33 individuals were recaptured one or more times, a total of 139 bats was handled. The repopulation of another roost during biweekly intervals following two successive removals of almost all bats present is recorded also. Analysis of these data suggest the following conclusions: 1) within a given population there may be multiple diurnal roosts among which individuals shift on a more or less daily and perhaps opportunistic basis (it has generally been assumed that vampires use a single home roost to which the same individuals return each day); 2) maximum foraging activity is restricted to the earlier hours of the evening; 3) vampires forage only after dark, the mean foraging time being estimated to be about 2 hours; 4) vampires seem not to utilize temporary nocturnal roosts in the usually Accepted sense, but return directly to a diurnal roost after foraging; 5) most individuals probably forage only once nightly; 6) heavy precipitation tends to suppress foraging activity; 7) differences in foraging pattern between the sexes were not apparent; 8) the amount of blood consumed may depend upon the length of the foraging period; 9) wild vampires probably consume not less than 20 per cent (of fasting body weight) more blood per diem than vampires in captivity, but variation from day to day apparently is great.