NH Winter Bat Surveys Reveal Decreasing Population

A little brown bat observed during the surveys. Photo by Sandra Houghton.

CONCORD, N.H. — Recent surveys for bats in New Hampshire hibernacula, places where bats spend the winter, resulted in biologists finding a total of only 26 bats.  In 2008, the same hibernacula had nearly 4,000 bats.

Bats in the state have suffered from extremely high mortality rates since White Nose Syndrome (WNS) was first documented in New Hampshire in 2009. Little brown bats, previously the most numerous bats in the Northeast, are sustaining the largest number of deaths.  Counts of little brown bats dropped from 3,135 bats in 2008 to just one in 2018.  Northern long-eared bat populations have also been decimated by WNS.

“I did not have a great deal of hope to see increasing numbers of hibernating bats during the 2018 surveys, but the continued lack of recovery remains disconcerting and of great concern,” said Dr. Jacques Veilleux, Professor of Biology and Environmental Science at Franklin Pierce University. “I do retain hope for the future return of our hibernating bats in New Hampshire, but should the recovery happen, it is likely to take many decades.”

The fungus that causes WNS, Pseudogymnoascus destructans, grows into the skin of the bat’s wing, damaging the skin, muscles, and blood vessels. There is no treatment yet for the fungus. This disease has killed over 90% of little brown and northern long-eared bats in the Northeast. WNS has continued to spread rapidly, and is now found in 31 states and five Canadian provinces. It has killed millions of bats since it was discovered in New York State in 2006. Since bats generally have only one pup a year, it will take many decades for the population to rebound, if they ever do.

Finding only one little brown bat this winter does not mean they are gone from the state.  Some bats fly to hibernacula in Vermont and New York and spend the summer in New Hampshire.  We are seeing female bats raising their pups and returning the following summer.  Maternity colonies in barns and homes are also monitored by homeowners under a citizen science program. Homeowners simply go out at dusk and count the number of bats that exit when it gets dark enough. The survey takes about 20 minutes to complete. To download survey forms and instructions, visit www.wildnh.com/surveys/bats.html.

Source: NH Fish and Game. For more information on New Hampshire’s bats, visit www.wildnh.com/nongame/bats-nh.html. The US Fish and Wildlife Service offers more information about the impact of White Nose Syndrome at whitenosesyndrome.org.

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