Mexican free-tailed bat in a gloved hand, image

The Mexican free-tailed bat, shown here in a gloved hand, is only about 3.5 inches long and weighs about 0.43 ounce.

bats up against the sky taking off at dusk, image

Bats take off at dusk in search of insects, their favorite food.

Mexican free-tailed bat spread out on a white rock, image

The Mexican free-tailed bat uses echolocation to navigate and find its prey.

Bats! Yolo Causeway's Secret Guest

Road Journals Blog—At first glance, the Yolo Causeway appears pretty humdrum: a 3.2-mile, elevated portion of Interstate 80 passing over a seasonal flood plain between the cities of Davis and West Sacramento, Calif. But of the many thousand motorists who cross it each day, few have any idea that just below the roaring traffic lies something truly extraordinary.

The crevices underneath the Yolo Causeway are home to more than 250,000 bats, making the adjacent 15,830-acre Yolo Bypass Wildlife Area one of California's best spots to view the world's only flying mammals. Admittedly, many people find bats creepy. You know, vampires and bats-in-the-hair and all. But how can you not be fascinated by animals that include 1,200-plus species, represent about one-fourth of all mammals, and eat their body weight in food each night, the human equivalent of a body-height stack of pizzas?

The vast majority of Yolo Causeway bats are of the Mexican free-tailed species, Tadarida brasiliensis, and they're mostly a maternal colony, according to Mary Jean "Corky" Quirk, an environmental educator and self-taught bat expert for the Yolo Basin Foundation. The bats are migratory, returning by June and giving birth around July 1. The pups learn to fly by mid-August and, during September, start to migrate away.

Since 2006, from June into September, Quirk has led a series of three-hour, family-friendly Bat Walk &Talks around sunset, when bats stream from their roosts to feed on insects. Looking for an unusual happy hour? Join Quirk for her August 23 Batty for Bats event that pairs bat viewing with wine and hors d'ouevres. No insects will be served— except to bats.

Photography by USFWS/Ann Froschauer (two of bats); Jane Reckner (bats in flight)

This blog post was first published in June 2014. Some facts may have aged gracelessly. Please call ahead to verify information.