By: Pawel Pieluszynski
All images courtesy of author
“Can someone from horticulture please come to Pier 3? There’s a bat on the lawn.” A static-filled transmission had suddenly blurted out from my walkie-talkie. At Brooklyn Bridge Park the horticulture team is passionate about what we call “ecological horticulture,” so we are not only caretakers of the flora of the park, but the fauna that is heavily dependent on it. Think of it as a more holistic approach to gardening. Stewards of our land and ecosystem, if you will. Other departments within the park are aware of this philosophy, so they will often let us know via radio if an injured songbird, possum, or in this case, an errant bat, needs some help.
As someone who is no stranger in assisting our furry, flying friends (I had just helped get two other bats to a wildlife rehabilitator in previous weeks), I decided to heed the call and promptly headed over to Pier 3. When I got there, my colleague who had originally made the radio call pointed the poor creature out. It was a handsome Eastern red bat, Lasiurus borealis, lying helplessly on the walkway, amongst a pile of fallen leaves. Upon some inquiry, I had found out that the bat in question was blown out of a leaf pile that was under a tree using a leaf blower. Previous research had informed me that Eastern red bats were tree-dwellers, so I assumed that the bat had fallen from its arboreal roost into the leaf pile due to illness or injury. Wanting to help, I proceeded to scoop up the bat in a cardboard box (bats should only be directly handled by vaccinated professionals, as they can carry rabies) and took it to the safety of our horticulture lab. While in the lab trying to get in contact with a wildlife rehabilitator, I noticed that the bat had become very active in its box. Taking this as a sign the bat might indeed be able to fend for itself, I took it to our nursery and released it into a safe Cryptomeria tree, where it promptly took refuge under a branch. When I checked the next morning, the bat wasn’t there leading me to believe it had flown away during the evening. Although it was a happy ending for the bat, the story hadn’t quite ended for me.
Eastern red bat, Lasiurus borealis, found after being blown out of a garden bed by a leaf blower. By Pawel Pieluszynski
Bat after being safely relocated to a tree. It flew away unharmed later that evening.
Curious about the cold-weather roosting habits of Eastern red bats, I decided to do some more internet research. As I had previously mentioned, I knew that the Eastern red was a solitary, tree-roosting bat species, as opposed to the more gregarious, cave-roosting species. They are also highly migratory and fly south to more hospitable climes during the colder winter months. Being tree-dwellers, Eastern red bats don’t hibernate like their cave-dwelling brethren do. Instead, when temperatures drop, they enter a lower metabolic state known as torpor. This allows them to become readily active with seasonal fluctuations of temperature, and they can even be seen flying around on unseasonably warm winter days. Now, a bare, exposed tree isn’t exactly a cozy place for an Eastern red bat when temperatures dip below freezing, so they seek other refuges. What I found out next really surprised me. Previously unbeknownst to me, when it gets cold out, Eastern red bats nestle in piles of fallen leaves! This previously unknown behavior was apparently first observed by foresters conducting prescribed burns, who noticed bats escaping leaf litter as fires encroached (Smith 2020). Studies from the U.S. Forest service have found that piles of decaying leaf litter and the ambient heat they generate protect bats from deadly deep freezes and that “energy savings from roosting under litter were two to three times greater than remaining in ambient air during periods of freezing weather, and around five and a half times greater when roosting under leaf litter with snow cover” (Farmer 2014). The moisture found in the leaf litter may help keep the bats hydrated as well!
It turns out that the bat I found wasn’t ill/injured, but a perfectly healthy individual that was resting happily in a leaf pile on a chilly day until it was rudely awoken by a leaf blower! As our practices in horticulture evolve, we are now finding out that traditional “scorched earth” policies regarding fallen leaves are not conducive to a healthy ecosystem. Fallen leaves provide invaluable overwintering habitat for a whole biodiversity of insects, invertebrates, amphibians, and mammals, including bats! Fallen leaves can even provide sustenance to many organisms, such as the morbid owlet moth, Chytolita morbidalis, whose caterpillars feed on dead leaf debris. Since many bats, including the Eastern red bat, feed primarily on moths, you’d be doing them a double favor by not fastidiously raking up those piles of leaves in your garden beds. Bats are wonderful, mysterious creatures, and many species are threatened by habitat destruction and disease outbreaks. They provide a plethora of ecosystem services (such as consuming those dreaded mosquitoes that can ruin a relaxing summer night), and by making our greenspaces more hospitable for them, everybody wins. So, this winter season, let’s make sure our bat neighbors are extra cozy and “leaf” the leaves!
The morbid owlet moth, Chytolita morbidalis, not only uses fallen leaves as habitat, but feeds on them as a caterpillar. Moths like this are a major part of a bat’s diet!
About the Author:
Pawel Pieluszynski specializes in ecological horticulture at Brooklyn Bridge Park with a keen interest in entomology and native plant communities. He is passionate about using horticulture as a tool to facilitate biodiversity and promote nature conservation on a local level. You can contact him at PPieluszynski@bbp.nyc or connect at Paweł Pieluszyński (@metro_mushitori)
Sources
Farmer, Sarah. “Leaf Litter Keeps Ground-Roosting Bats Warm.” US Forest Service, 6 May 2014, www.fs.usda.gov/features/leaf-litter-keeps-ground-roosting-bats-warm.
Smith, Joseph. “Eyes on the Leaf Litter!” 2020, www.smithjam.com/eyes-on-the-leaf-litter/.