Every evening from March to November, approximately 1.5 million Mexican free-tailed bats emerge from under the Congress Avenue Bridge in what is one of the great wildlife spectacles of North American cities. The emergence begins about 20 minutes after sunset and can last 45 minutes — a continuous dark spiral of bats pouring out over Lady Bird Lake and heading north and west to feed on moths and other insects.
The best viewing spots are on the bridge itself, on the lower trail along the lake's edge, or from a kayak on the water below. Bat viewing parties and guided kayak tours are available throughout the season. The colony is largest in August, when the pups born that summer are old enough to fly. The sheer scale of the emergence — and the sound, a continuous low chirring as the colony pours out — is genuinely one of Austin's unmissable experiences.