We had a great time last night conducting a Bat Walk to mark the third anniversary of the founding of Shoal Creek Conservancy, here in Austin.
Bat fans showed up on the second night of cool weather to see if bats would fly from under the 9th St. Bridge in Duncan Park.
Though the cool weather felt great to us after a long extended hot summer, the bats were snug in their expansion-joint crevices under the bridge and did not want to drop out into the cool night.  The temperature had dropped to 43 degrees F the previous night and that night’s dew point of 47 F promised another cool night ahead.  Since fewer insects fly below 50 F, they must have decided to conserve their energy budget and stay snug in the roost.  Here’s a thermal imaging snapshot of the crevice we inspected.

thermal image crevice 9th St. Bridge Duncan Park

Those are bat bodies showing white and their reading was about 88 deg F on the outside of their fur.  Their body heat kept the crevice nice and warm, 82.6 deg F here next to the bats in this snapshot, 15 degrees warmer than the blue-colored bridge outside the crevice.  It would take a lot of snuggling to re-create all that warmth, so perhaps they just hunkered down to wait out the cooler nights.  Low temps will be back in the 60s for the next two weeks, so I think they made the right call.

Great group of people at Shoal Creek Conservancy; we’re so happy there is a unified voice to speak up on behalf of beautiful Shoal Creek!
Thanks to all who came out to hear our talk and watch our radar images of Central Texas bat activity.  Next year we’ll unveil the new SonoBat Live and if we get a warmer night, we’ll all be able to see real time sonograms of the echolocation calls of flying bats.