The Social Language of Bats
February 4, 2025
Bats can use sounds in many complex ways. They can sing and even have different dialects… When imagining a bat, the first thoughts that come
“Just like the old days, eh Heather?”
Kent softly clicks his tally counter as he sits in his folding chair on the other side of the largest cluster of bat houses at Stonefield Historic Site. Bats are pouring out of the bat boxes Kent began building and installing over 20 years ago. I agree – watching this is just like the days before white-nose syndrome (WNS) arrived in the region. “I haven’t seen this many bats in years,” I remarked to Kent. It’s a rewarding sight.
In total, there are 27 bat houses in three clusters, and one recently installed bat condo at Stonefield. There’s a variety of shapes, shades and sizes of bat houses across the property – and all of them are inhabited by little brown bats (Myotis lucifugus) (and the occasional big brown bat, Eptesicus fuscus). Kent Borcherding has been building and experimenting with bat house design since the early 1990s and Stonefield has been one of the beneficiaries of Kent’s work.
Stonefield Historic Site sits on the Mississippi River near Cassville, Wisconsin. Like many old buildings pre-WNS, several were used as summer roosts by little brown bats. It’s hard to know exactly how large the colony was before the bat houses were provided. Though estimates were in the thousands, monitoring summer bat colonies began only recently in Wisconsin. What is known is that soon after Kent installed four bat houses and bat eviction from buildings began in 1998, the bats moved to their new homes with gusto. Kent started keeping track of bat box occupancy in 1999, checking for bats during the day and noting how full they were. Hundreds and soon thousands of bats eventually moved into the growing number of bat houses.
The Wisconsin Department of Natural Resources Bat Program started coordinating bat emergence counts at roost sites across the state in 2010 and the first “official” emergence count at Stonefield was in July 2013. What started with a small handful of bat counters turned into bat blitzes where 15-20, mostly local folks congregate to survey the emerging bats several times each summer. Before WNS arrived in the Midwest and began affecting hibernating bat populations, counts of Stonefield’s bats frequently topped 3,500 with the highest counts of nearly 4,000 in July 2015 and 2016.
WNS arrived in Wisconsin in March 2014, though the neighboring states of Michigan and Illinois had infected sites for at least a year before Wisconsin’s first occurrence. The story looked the same for many of Wisconsin’s hibernating bats. As often occurred in other states – we recorded massive declines. Monitoring little brown bat summer colonies revealed losses of roughly 75% at bat houses, barns, and attics. Many winter colonies in Wisconsin had similar fates. We lost a lot of bats, but in recent years we have been seeing a departure from the usual WNS story.
Summer colonies of little brown bats stabilized about 3 years after WNS impacts and, in some cases, have been increasing in the last couple of years. The colony at Stonefield dropped 66% from 3,750 bats in 2016 to 1,280 in 2017. The colony held steady at about 1,300 bats for several years. Then, 2022 counts revealed increasing numbers. We saw a jump in 2022 to 2,500 bats, 2,800 in 2023 and in July 2024 we counted a whopping 4,200 bats. Emergence counts are always going to be a rough estimate of bat colony size since there are many things that affect how well one can count bats as they drop out, but what’s clear is that we recorded a decline, stabilization, and recent recovery of little brown bats at several locations in Wisconsin.
Recovery of summer colonies has not looked the same across the state. Some sites like Stonefield and others along the Mississippi and Wisconsin Rivers as well as the Lake Michigan shoreline are doing well post-WNS declines. Other colonies at roost sites, in northern Wisconsin in particular, are not recovering as well or as quickly.
Learning why some bat colonies are recovering better than others is important for understanding impacts to bats from WNS. Where do surviving summer bats go to hibernate in winter? Is there something about the summer roost sites that is helping bat colonies persist? Are bats changing their seasonal behavior and arriving or departing sites earlier or later? There are many questions we seek to answer about why little brown bats continue to thrive in the face of WNS, but it’ll take time to figure out. For now, we’ll enjoy the flutter of thousands of bats emerging for their nightly foray – just like the old days.
About the author:
Heather Kaarakka is a conservation biologist for the Wisconsin Department of Natural Resources Natural Heritage Conservation Program. She works with other biologists, citizen-scientists, landowners, and volunteers to monitor, study, manage and protect bats and their habitats in Wisconsin. Her work focuses primarily on summer roosts for bats and she coordinates the summer roost monitoring project for the Wisconsin Bat Program.
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Madelline Mathis has a degree in environmental studies from Rollins College and a passion for wildlife conservation. She is an outstanding nature photographer who has worked extensively with Merlin and other MTBC staff studying and photographing bats in Mozambique, Cuba, Costa Rica, and Texas. Following college graduation, she was employed as an environmental specialist for the Florida Department of Environmental Protection. She subsequently founded the Florida chapter of the International DarkSky Association and currently serves on the board of DarkSky Texas. She also serves on the board of Houston Wilderness and was appointed to the Austin Water Resource Community Planning Task Force.
Michael Lazari Karapetian has over twenty years of investment management experience. He has a degree in business management, is a certified NBA agent, and gained early experience as a money manager for the Bank of America where he established model portfolios for high-net-worth clients. In 2003 he founded Lazari Capital Management, Inc. and Lazari Asset Management, Inc. He is President and CIO of both and manages over a half a billion in assets. In his personal time he champions philanthropic causes. He serves on the board of Moravian College and has a strong affinity for wildlife, both funding and volunteering on behalf of endangered species.