White-nose syndrome taking toll
State conservation biologists radio-tracking cave bats to learn more about their summer habitats are also turning up insights into the strength, stamina and sacrifices of mother bats.
A federal grant is funding the multi-year project with Minnesota and Michigan to learn more about several hibernating bat species that use forests extensively in summer and whose populations have been decimated by white-nose syndrome in eastern states in recent years. The information will help continue to allow forest management that will ultimately benefit the bats.
“Unfortunately, we’re unlikely to find something to stop the disease in Wisconsin, so we are trying to gather information that will allow us to do the best job in managing bats in the post white-nose syndrome landscape,” said Heather Kaarakka, a state Department of Natural Resources conservation biologist and one of the researchers.
White-nose syndrome is a deadly disease of bats that does not affect humans, but covers bats in a fungus that awakens them while they are hibernating, burning precious energy stores and leading to starvation. White-nose syndrome was first detected in Wisconsin in 2014 and has spread across the state. Sites where the disease was first documented have seen some bat populations decline by more than 90 percent.
Bats play an important role in Wisconsin’s ecosystems and economy. They are voracious insect eaters, with a 2011 North American study estimating bats save Wisconsin’s agriculture industry between $658 million to $1.5 billion annually in pesticide costs.
To conduct their research, Kaarakka and DNR biologists Paul White, Katie Luukkonen and Jennifer Redell set up fine mesh nets in the bats’ travel corridors. When a bat of interest, either a Northern long-eared bat or an Eastern pipistrelle, flies into the net, they quickly retrieve it and if it’s a female of a species of interest, they attach a small radio transmitter between the shoulder blades using nontoxic, temporary glue.
The researchers return on subsequent days and nights to find the bat and track it back to the tree where it roosts; count bats emerging from the roost; and assess and catalog information about the habitat, including the tree species, height of the roost, proximity to water and more.
The research has revealed that Northern long-eared bats are incredibly adaptable to the environment they are in, White said.
They use a lot of different tree species – live and dead trees – and are found in the crevices or under bark that is sloughing off the trees.
“We do think they can positively respond to sustainable forestry,” White said.
Radio-tracking of Eastern pipistrelles started in 2016 and will continue next year to further understand their habitat needs. First-year results revealed bats roosting in leaf clusters in trees in small groups of six to 14.
Eastern pipistrelles may forage as far as 2 miles away from their roost and are switching roosts much more than expected. The mothers may be moving their pups every 1 1/2 days, perhaps to stay ahead of predators. The pups grab onto the mother, no small feat for a flying mammal that weighs only seven to nine grams.
“Male bats have a pretty easy life,” White said. “They mate and feed themselves. The females leave the hibernation site early, give birth to one or more pups, nurse the pups and feed themselves. All of that makes it very challenging for a female bat to survive.”
Across their field work, the researchers captured more male Eastern pipistrelles in their nets than females. White worries this imbalance may be a sign that white-nose syndrome has killed females and fewer of them are out on the landscape this summer.
All of the data DNR researchers collect will be provided to a contractor that will also get information from Minnesota and Michigan researchers and use the information to develop a bat habitat conservation plan for the upper Midwest.