The small, migratory bat called the Mexican free-tailed bat is very common in Napa County, especially as the weather warms.
They fly extremely fast, up to almost 100 miles per hour. They live in extremely large colonies, the largest is in a cave outside of San Antonio TX with about 20 million bats, says Quirk. "Locally our colonies are smaller, but still in the thousands. Pregnant and nursing females in the summer eat about their body weight in moths and mosquitoes nightly."
Quirk also notes that Mexican free-tailed bats have an extremely large baby, compared to the mother's size. "Her pup is about 1/3 her weight at birth. Luckily for the mom, most bat species only give birth to one baby per year. Of course that means they are very slow to reproduce and don't recover well from tragedy to a colony."