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# The bat nado rises at sunset
- URL: https://www.earthtoseanews.com/yolo-causeway-bats/
- Published: 2026-08-25T23:47:43.000Z
- Updated: 2026-09-05T08:33:26.000Z
- Description: The Yolo Causeway carries Interstate 80 over the marshes west of Sacramento. Underneath it lives California's largest city bat colony, and watching it leave is free.
- Author: Nicole McMahon
- Tags: Explore, All stories

The causeway was built more than a hundred years ago to lift the highway over the floodplain of the Yolo Bypass, and some time in the 1970s the bats found it. Mexican free tailed bats, each about the weight of a couple of coins, tucked themselves into the expansion joints along the underside of the bridge, and they have come back every summer since. Today the colony numbers around two hundred and fifty thousand. From June to August, at sunset, they pour out in long ribbons that twist across the sky for twenty minutes or more, a sight the locals have taken to calling the bat nado. The Yolo Basin Foundation runs talks and guided tours on summer evenings, and Corky Quirk, its program coordinator, has been leading them since 2004, usually beginning with a gentle word to the thirty or so people gathered not to bother the animals. You do not need a tour. A viewing area beside the bypass is open to anyone who turns up before dusk.

Read the full story: [Under a Sacramento bridge, California’s largest urban bat colony takes flight every night](https://www.kqed.org/news/12092538/under-a-sacramento-bridge-californias-largest-urban-bat-colony-takes-flight-every-night), by Srishti Prabha, KQED. Tour details from the [Yolo Basin Foundation](https://yolobasin.org/bat-talk-tours/).

The bats spend their nights over the rice paddies of the Sacramento Valley eating moths and mosquitoes, and the farmers below them have done the maths. Charlie Russell, a volunteer with the foundation, points to one grower who never sprays for armyworm, the moth whose caterpillars chew through rice crops, "because he's got a quarter of a million bats taking care of the moths." Free tailed bats have been clocked at around a hundred and sixty kilometres an hour, faster than a cheetah, and they will climb miles into the air after their prey. "Bats are pretty misunderstood," Quirk says, "and often when people learn more about them, they begin to appreciate them. And we protect what we care about." Linda Harter, who has volunteered on the tours for more than a decade, keeps her review shorter. They are amazing. The colony heads south again as the northern autumn closes in, so the last evenings of this season are happening now.

### Questions you might have

**Do I need a ticket to see the bats?**  
No. The viewing area beside the Yolo Bypass is open to anyone who arrives before sunset. The Yolo Basin Foundation's guided talks and tours are the extra, and they book out in summer.

**Is it safe to stand near a quarter of a million bats?**  
Yes. You watch from the ground as they leave high overhead. The one rule, and the first thing Corky Quirk tells every group, is never to touch or disturb a bat, for its sake and yours.

**When does the season finish?**  
The colony leaves as the northern autumn sets in, so the last flyouts of this year are happening now. They come back in late spring, around May or June in the northern hemisphere.

Our short take: the full story is by **Srishti Prabha** for **KQED**, 31 July 2026\. Tour details from the Yolo Basin Foundation. Photograph: Eric Knight, CC BY, via iNaturalist.