YOLO COUNTY -- Alongside the bumper-to-bumper traffic of the Yolo Causeway, just a few miles from downtown Sacramento, the Yolo Bypass Wildlife Area is like a hidden treasure in plain sight.
But what can’t be seen during the day are the estimated 250,000 bats that live inside the causeway structure during the summer.
If you know where to look, you can see them in magnificent numbers streaming out at sunset to eat their weight in bugs all night.
"You know, it changes every night. There's always something new to see," said Corky Quirk, the founder of NorCal Bats.
Quirk is the tour guide for the summer bat tours offered through the California Department of Fish and Wildlife and the Yolo Bypass Wildlife Area.
The program starts with an indoor, multi-media talk where the public learns all about the flying mammals.
Quirk even hooks up a live camera to a projector, so people can get an up-close look at the bats eating.
Then shortly before sunset, everyone caravans out to the wildlife area to be in position for the main event.
What about the Yolo Causeway makes it so attractive to bats?
"I think a lot of it is because it's just a really safe, hot place. The freeway, it's black on top, so it absorbs the heat," Quirk explained. "Predators just can't get into those crevices, they're 20 and 40 feet high. Feels like rock, you know, so it feels kind of like the caves would feel, which these are historically cave bats."
The tours are offered several nights a week and July is all sold out, but there are plenty of opportunities in August and September. Advanced reservations can be made through the Yolo Basin Foundation's website.