Bats of the United States and Canada

Inventories

recto runninghead 79 Inventories Techniques to inventory bats include searching caves known to have been inhabited by bats and attempting to locate additional caves occupied by bats. Estimates of populations are made by actually counting the number of bats hibernating in caves or mines, or by estimating numbers emerging to forage. For bats that cluster together during hibernation, estimates are made by multiplying the number of bats in a square meter by the area covered by bats. Sometimes, clusters of bats are photographed and then counted later. Mexican free-tailed bats (Tadarida brasiliensis mexicana) exiting a cave in Texas. It is difficult to estimate the number of bats exiting a cave when large populations are involved. Michael J. Harvey 80 bats of the united states and canada For bats inhabiting caves or mines during summer, estimates may be made as the bats emerge. However, these estimates often are inaccurate , especially if large numbers of bats are involved. A relatively new technique, the use of thermal-infrared-imaging cameras, has proven to be superior to estimates made by direct counting. There is increasing evidence that, in the past, estimates made from direct counts of emerging bats greatly overestimated the number of bats exiting roosts in caves or mines. ...