One, Two, Three Bats at the Fish Hatchery?!
By Mary Jelf, Leadville Today Contributor
On a recent moonlit night, a group of volunteers gathered in the cool air, armed with lawn chairs and clickers to gaze at the wall of the Leadville National Fish Hatchery, to observe and count bats.
There is a maternity roost of little brown bats in the top of the historic building where bats hang and keep each other warm during the day. Around twilight, they leave the roost in search of food, which is generally insects. According to Jeni Windorski of the US Forest Service (USFS), each bat can eat its own weight in insects every night, making them very useful in keeping the insect population in check.
Why count the bats? To keep an eye on changes in their population numbers. The Myotis lucifugus species is being affected by a disease called white nose syndrome, which started in the Eastern US, but is spreading westward. By counting bats at different locations during their summer residency, the USFS can work to identify what factors may change how they live.
Bats tend to roost in high parts of buildings, caves, and mines. Windorski reported that when places are found to have bats, efforts are made to keep those spaces open for the animals with bat gates and other methods. When the roof at the fish hatchery building was recently updated, the new design took into account the need for bats to enter and exit from both sides of the building.
Lin Denham participated in a bat count recently at another location where her post only counted two bats. “I wanted to see more bats,” she replied, when asked why she came back for another round.
In addition to actually counting the bats, Windorski also sets up an SM2 Bat Song Meter, generically known as a “bat detector”, to record their ultrasonic echolocations. These vibrations are not audible to humans, but can be analyzed in a lab to identify bat species by their unique signature. If we could actually hear this, it would be loud like a smoke alarm. During the count, Windorski also uses a device that picks up the ultrasonic waves and translates them into a frequency we can hear as clicks. There is a ramping up of clicks just before a bat emerges from the roost to help with a successful exit. Windorski says that there is also a rev of clicks when a bat gets close to prey. They send extra clicks to hone in on an insect, then knock it unconscious with their wings, catch it in the membrane that stretches between their legs and tail (the uropatagium), and scoop it into their mouths.
When counting bats, one must be vigilant and not count the ones that circle back and roost near the exit for a time. They come out as singles, or in groups of two or three. It can also be tricky not to count bats that exit from one side of the building, but then cross over to the other side. The trick is to keep your eye right on the exit point, then make just one click per bat.
During the count, observers noted that some bats were exiting sooner than expected, when conditions were lighter. Windorski noted that sometimes scouts are sent out before the rest of the colony to check conditions and report back. It also could be caused by hunger, since a big storm the night before may have cut short their feeding time.
The count ends when it is either too dark to see the bats or after ten minutes pass from the last bat seen. The numbers from clickers at each exit point are added and average to get an accurate number. The number from this count was 499 bats. This is lower than the 811 bats counted earlier in the summer, which is normal.
“The babies are mostly grown now, which would mean less total bats here, “said Windorski. “The cooler weather can also cause an earlier start to migration.”
After an evening paying such close attention to bats and learning about their habits, it was interesting to note that they live this way, each and every day, whether visitors to the fish hatchery – or counters with clickers – are there to notice or not.
LT Contributor Mary Jelf practices living joyously in the high country. She relies upon beginner’s luck and the kindness of strangers. Some days she turns thoughts into words to share to make the world a better place.