Bats galore

A few months ago we drove over the Yolo Causeway at sunset. To our delight, we saw thousands of bats flying out from under the road. So last night, we decided to picnic near the bridge (about 3 miles from our house) and watch the bats. . . We arrived at 7:30 and checked out the belly of the bridge. From our experience in Austin, we knew we were in the right place because of the feces on the ground and the distinctive smell wafting out from under the causeway. Within minutes, thousands of bats emerged, flying out from under the bridge so quickly that the camera could only catch blurred images. As they emerged, the smell intensified. Interestingly, they seemed to fly out from the bridge disorganized, but gathered together into an organized flume of bats heading Southward.

Here's a video we shot (FYI: the video does not show up on Bloglines. So if you want to see the videos, you should go to our actual blogsite if you rely on Bloglines to read the posts):

Bat Emergence Times at the Yolo Causeway:
Jan - Mar (migratory, not in area)
April - 7:45 PM
May - 8:15 PM
June - 8:30 PM
July - 8:30 PM
August - 8:00 PM
September - 7:15 PM
October - 6:30 PM
Nov - Dec (migratory, not in area)

I believe these bats are Mexican free-tail bats, the same as those found in Austin TX. Click here for a study about Central Valley bats conducted in Yolo County.

In April, thousands of mostly female, pregnant Mexican free-tailed bats migrate North to give birth. I have no idea how many bats are living under the Yolo Causeway, but in Austin, they estimate 0.75-1 million live under the famous Congress Avenue Bridge. There is much more space under the Causeway, so I imagine that there may be more here? In Austin, they estimate that the bats consume from 10,000 to 30,000 pounds of insects each night! Moms give birth in June or July and the bats and pups head back south in October.

Our Mexican free-tailed friend is of the Family Molossidae, and Genus species Tadarida brasiliensis.

Approximate North American Range:

A closeup profile of our buddy Tadarida brasiliensis:

One more video: