The worlds largest colony of Mexican Free-tailed bats migrates from Mexico to a natural cave near San Antonio, Texas every year for the spring and summer months. They come to give birth and to fatten up for the winter before heading back south.
I was lucky enough to get the opportunity to go and photograph and watch the return of the colony after staying out all night feeding. These are some of the images from Bracken Cave where they nest.
Bracken Bat Cave is located near the Natural Bridge Caverns and the grounds are quite nice. Here are some images of the surrounding area.