When your field trip involves wildlife watching, you can't be sure how it is going to go. The Conway Bats emergence time is usually somewhat predictable. Shortly before sunset. But not last night. Thanks to Javier, our field trip was still educational and fun. We just saw way less bats than we were hoping. Only one or two bats here and there were spotted leaving their roosting place by binoculars. Our bat devices were frequently detecting a few, occasionally clearly enough they must have been flying right overhead. But only small numbers. The bat colony never emerged in mass like usual. We kept thinking they were about to come out so we had lots of time to discuss and learn about them. We did a lot of speculating why they weren't coming out as we waited. It had been a very hot day, around 100°F, and it was pretty windy near sunset. Maybe they were waiting to cool off? Maybe they hoped the wind would die down to make hunting and flying easier? We started 40 minutes before sunset, but could they have come out earlier than usual, before any of us arrived? I bet they all came out soon after we left.
Bats are the only mammals that can fly. They have wings made of skin and a unique bone structure that allows them to fly with great agility and speed. Bats are important pollinators, and they play a crucial role in the pollination of plants like avocados, mangos, bananas, and agave, which is used to make tequila. Contrary to popular belief, bats are not blind. They use echolocation, a biological sonar system, to navigate their surroundings and find prey. Bats eat a wide variety of food, and many in the United States are insectivores, consuming agricultural pests, which makes them an excellent form of natural pest control.
According to our bat detectors (Echo Meter from Wildlife Acoustics), we heard possibly 10 different species. These detectors use software to compare frequencies and patterns of the bat's echolocation to narrow down the species. Of course, you can't rely completely on software to make the determination. But I haven't studied bats enough to know the species from their different spectrograms myself. The most common species identified last night by far were Hoary Bats and Mexican Free-tailed Bats.
The most common species of bats in the Rio Grande Valley are Mexican Free Tailed Bats. In March 2017, the city of Mission Tweeted: "250,000-400,000 Mexican Free-Tailed Bats are living in the crevasses of our Conway & Exp 83 overpass & you can see them take flight nightly!"
This article from the University of California has some good info about "Visual Listening" to bats by analysing their spectrograms. We have a bunch of bat enthusiasts in our chapter, but if any of our members really want to get into learning about bats and identifying them by sound, let me know. The USB-C Bat Detector device I used plugs into Android phones and belongs to our TMN Chapter. I would love for someone else to delve deeper into bats than I have. Bats have always interested me, but my focus remains spiders and insects.
During the field trip, we were asked about details on bat houses. Bats can be particular. Sometimes a perfectly good bat house will go un-occupied. From research I have done, bat houses should be placed to receive 6 to 8 hours of direct morning sunlight, usually facing South. Placed near trees, but not shaded by them. Located within 1/4 mile of freshwater. And the house should be airtight around the roof. You can read more here.
It is important to remember, never pick up a bat you find on the ground with bare hands. Bats can carry a wide variety of viruses, including coronaviruses, without developing disease symptoms. In some cases, bats may serve as a reservoir for viruses, meaning that the virus can persist within the bat population without causing illness.
If you want to see what time the bats are emerging, check out Mission Bats on Facebook which frequently reports the times bats are seen leaving their bridge roost.
Our next Chapter Meeting Presentation is on Gardening for Bats by our more prolific chapter blogger, Anita. Learn how native plants provide food and offer shelter for night-flying insects, and in turn, how that benefits bats. Follow us on Facebook for more info and to watch the presentation streaming live on June 19.