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Posts Tagged ‘Yolo Bypass Wildlife Area’

If you are in the Davis or West Sacramento area in the late summer or early fall, and have an evening to spare, go and find a spot where you can sit beside the Yolo Bypass Causeway. This is where highway I-80 crosses over the Yolo Bypass.

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Streams of Mexican Free-tailed Bats over the Yolo Bypass

Just as the sun begins to set, you will see an amazing sight. Columns of bat will flood out from under the bypass and stream across the sky in sinuous ribbons. About a quarter of a million Mexican Free-tailed Bats (Tadarida brasiliensis) live under the bypass this time of year, and every night they pour out and spread across the surrounding area to find small flying insects to eat.

These bats are incredible! They can fly about about 100 miles per hour, making them among the fastest mammals in the world! Remember that Cheetahs are the fastest land-mammal, but bats have them beat by a healthy margin. These bats can fly as high as a mile above the ground, and can forage out distances of several miles from their night roost before returning around dawn to sleep. Using their sonar they can detect and pinpoint the exact position of little insects flying through the air and then capture those insects on the wing, at speed!

My wife, daughter, and I joined some friends and went out for an evening visit to see the bats about a month ago. I was a spectacular evening in the Yolo Bypass Wildlife Area. We saw lots of Swainson’s Hawks; herons, egrets, and ibis galore; some of the biggest Western Saddlebags (which is a species of dragonfly) I have ever seen; and then we got to the causeway.

When we arrived, the sun was still a touch above the horizon, so we had some time to stand around the dirt road that runs parallel to I-80 and chat and watch the sunset. We got a very nice surprise when an adult Peregrine Falcon flew past and landed in the top of a tree a little ways to the west of us. I was so excited to see this bird that, in turning around for a better look, I clumsily stepped on my wife toes (sorry sweetheart)!

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Mexican Free-tailed Bats as they leave from under the Yolo Causeway.

As the light began to fade, we started seeing little movements under the causeway. The first bats were starting to move. Interestingly, the bats do not wake up, take flight, and simply fly out from under the causeway wherever they happen to be. Instead, they wake up, take flight, and then fly directly under the causeway for a few hundred yards before turning a sharp left, and lifting up into the open sky. I have no idea why they decide to do this, but volunteers at the Wildlife Area know it is gong to happen so consistently, that they can tell you exactly which tree the bats will fly out near.

The numbers of bats moving under the causeway built and built until there were bats streaming along between the support pillars. Then they made that left, and out in to open they came! A snaking stream of bats began raising and twisting into the sky! Thousands and thousands of bats following one another out from where they had been sleeping to look for food. As we watched the seemingly endless flow of bats, we got a very cool surprise. That Peregrine Falcon that we had seen earlier came back. It started strafing through the flow of bats. It was hunting bats!

I have seen this behavior of raptors hunting bats as they leave their night roost on video before, and it is pretty spectacular to see on a screen. Seeing it in real life was thrilling! After a couple of passes, the Peregrine made a quick move to one side, and suddenly it had a bat in one talon! It flew off and out of sight carrying it’s dinnertime snack.

The rest of the bats were generally nonplussed by the Peregrine attack, and keep streaming and streaming into the coming night.

Finally, the last bat that was going to leave had departed, and the darkness was getting deep enough that we would not have been able to see the bats fl by even if they were there, so we piled back into our cars and headed for home.

All in all, a terrific way to spend and evening!

 

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