Between Sacramento and Davis, nearly 250,000 bats take flight each night beneath the Yolo Causeway

You may have driven over the Yolo Causeway between West Sacramento and Davis countless times, but there is more than just traffic on the bridge.

The NorCal Bat Association says underneath the causeway lives a bat colony with almost a quarter million members. Each evening, they emerge from underneath the bridge and take to the sky in search of insects, including mosquitoes.

September is considered prime time for watching the bats emerge around sunset, drawing visitors who gather beneath the causeway with chairs, cameras and plenty of questions.

For visitor Ashley Manges, the experience was an unexpected surprise, as she watched hundreds of tiny silhouettes begin to fill the sky.

"It's gorgeous, isn't it?" said Corky Quirk, a certified NorCal Bats educator who leads educational programs about the colony.

"Those are bats"

Quirk said people who have driven across the causeway for years may have mistaken the bats for birds.

"But if you are seeing them at sunset, it's bats," Quirk said.

The colony beneath the causeway is one of the largest urban bat colonies in the region, and the bats play an important role in the ecosystem by consuming insects.

Quirk works with the Yolo Basin Foundation to educate visitors about bats through its bat education and tour programs.

The program includes a caravan tour where visitors learn about the animals before watching the colony emerge. Visitors can also see bats that are being rehabilitated by the Yolo Basin Foundation and take part in a question-and-answer presentation.

Quirk said the bats' physical characteristics help them move quickly through the air.

"They have a long, narrow wing, a sign of speed," Quirk said. "And these guys can fly faster than a cheetah can run."

Changing perceptions about bats

For Quirk, the tours are about more than watching thousands of bats take flight.

"Mostly I hope people learn bats are an important part of the environment and they are not scary animals, no reason to fear them," Quirk said.

Visitors often turn the experience into an evening outing, bringing chairs and settling in beneath the causeway as they wait for the bats to emerge.

The surrounding landscape provides plenty to watch while they wait, but the bats remain the main attraction.

"Watching kids play in the dirt and get in touch with the world around them in nature is a great part," Quirk said. "It is always good to see."

Then, as the sun begins to disappear, the bats start emerging.

The Yolo Basin Foundation Bat Caravan tours run through September and have a $17 registration fee.

NorCal Bats offers education on bats to schools year-round.

Quirk says you should never handle bats and always call for help if you see one on the ground for safety.