Predation on Corynorhinus townsendii by Rattus rattus

Corynorhinus townsendii (Townsend's big- eared bat) is a rare and declining species. Ex- tensive surveys for the coastal subspecies, C. t. townsendii, in California indicate that only 50% of historic maternity colonies are occu- pied currently (Pierson and Rainey, 1996). Three of the largest maternity colonies occur in Marin Co. Two of these have been moni- tored with evening exit counts on a regular basis since their discovery (1987-Randall House; 1990-Jerrys) through 1996. From 1987 through 1993, the Randall House colony slowly increased from 123 to 215 bats as the colony was afforded greater protection from disturbance once the bats were discovered. Since 1990, both colonies have been com- posed of ca. 200 adult bats in the spring, and ca. 300 adults and young through the summer and early fall.