Photographic estimation of roosting density of Geoffroy’s Rousette Fruit Bat Rousettus amplexicaudatus (Chiroptera: Pteropodidae) at Monfort Bat Cave, Philippines

Abstract

Conservation and management of bats requires reliable and repeatable data regarding the size and patterns of variation in size of bat colonies. Counts and densities calculated via photography have proven more accurate and repeatable than visual counts and ocular estimates. Unfortunately, the potential of photography to investigate the size of a bat colony and roost density has rarely been explored. In the summer of 2006, a colony of Geoffroys Rousette Fruit Bat, Rousettus amplexicaudatus, was photo-documented in the Monfort Bat Cave, in the Island Garden City of Samal, Davao del Norte, Mindanao, Philippines. We selected 39 images to develop roost density estimates. Mean (+or-SE) roosting density was 403+or-167.1 bats/m2 and 452.3+or-168.8 bats/m2 on the walls and ceiling of the cave, respectively; densities were not significantly different from each other (P=0.38). Based on these standardized data, we estimate that the initial 100m of the cave contained 883,526 bats. Ultimately, this photographic technique can be used to develop a statistical approach which involves repeatable estimates of colony size for Geoffroys Rousette Fruit Bats at Monfort Cave and will enhance ongoing monitoring activities throughout this species range.