By all accounts, the engineers who designed the Yolo Basin Causeway never imagined its design would provide the perfect summer roost for an estimated 250,000 migrating Mexican free-tailed bats (Tadarida brasiliensis). Nor did the designers anticipate that thousands of people would gather on summer evenings to witness and marvel over what locals call “the flyout.”
The three-mile elevated roadway between Sacramento and Davis, California – once noteworthy for its innovation in providing motorist access over a broad expanse of environmentally significant wetlands – is now perhaps equally noted for attracting and hosting hundreds of thousands of bats during warm weather months.
Every summer, Mexican free-tailed bats faithfully make their way to the Yolo Basin Causeway to roost tightly between the causeway’s expansion joints, below the road’s rumbling traffic, above marshy wetlands thick with insects, and generally inaccessible to prowling predators. Notably, the causeway’s concrete retains the warmth of the sun for pregnant bats to give birth to their pups. As the sun sets, thousands of ravenous bats rise into the sky in a ribbon-like formation, weaving through the sky.
While there are several places near the causeway to watch the bats’ remarkable emergence, the Yolo Basin Foundation provides summertime Bat Talk and Walk events that begin with a presentation on bats followed by a tour of the wildlife area’s wetlands and rice fields. Then, bat watchers settle in place to observe “the flyout.”
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- Bat Talk and Walk events offered by the Yolo Basin Foundation are family-friendly and last about three hours. Adults are charged a modest fee; children under 15 are free. The events are offered from June through September and sell out fast.
- The Yolo Basin floodplain was once an 80,000-acre wetland marsh. While conservation acreage has been whittled down over the years, the Yolo Bypass Wildlife Area continues to be vibrant with wildlife. Once inhabited by herds of tule elk, the vast wetlands are home to beavers, muskrats, river otters, turtles, toads, snakes, and nearly 200 species of birds. The wildlife area is open every day except Christmas and is always free.