This time of year, if you sit near the hawk bench at the Model Boat Pond at dusk, you’ll see lots of Chimney Swifts feeding.  But as it gets darker, almost like magic, there are fewer and fewer swifts and in their place you’ll see bats. 

Using a “bat detector” to monitor the pitch of the echolocation sound, I discovered the bats are primarily two species, Eastern Red Bat and Big Brown Bat.