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Bats on the Brink


A big brown bat (Photo: Logan Parker)

A big brown bat (Photo: Logan Parker)

Despite popular belief, bats are friendly, useful creatures that protect humans from disease. And their numbers are plummeting.

In 2015, the Northern long-eared bat was listed as a federally threatened species. In Maine, the Northern long-eared bat and the little brown bat have been listed as endangered and the Eastern small footed has been listed as threatened.

White-Nose Syndrome (WNS), a disease caused by a cold-tolerant fungus was first documented in New York in the winter of 2006-2007 and has since decimated populations of cave bats in Maine and over 5.7 million bats across the Northeast. Maine has lost more than 90% of its cave bat population.

Maine Bats

Cave Bats

Maine’s five species of cave bats include two that you might see in your attic, garage or barn. Big brown and little brown bats typically gather in colonies in late spring through summer where the females raise their single pups. You are unlikely to encounter the other three species (Eastern small-footed, Northern long-eared and tri-colored bat) as they spend their summers alone or in small groups in the nooks and crannies of trees during the day and forage for insects at night.

All these bats, however, spend their winters together, typically hibernating in large groups in caves. Although we know that some overwinter in human structures, we don’t know the size or extent of those wintering populations. All five species of cave bats have been affected by White Nose Syndrome.

Tree Bats

Maine has three species of tree bats – hoary, red and silver-haired. These bats roost and have their pups individually or in small groups under the bark or in the cracks, crevices and cavities of trees, and occasionally within human structures like houses and barns. These bats leave Maine each fall to spend the winter in the southern United Sates, and return each spring.

Threats to Bats

White Nose Syndrome

The deadly, cold-loving fungus (Pseduogymnoascus destructans) that causes White Nose Syndrome arrived in Maine in 2011 and has since killed 90% or more of the bats hibernating in Maine’s three known hibernacula (caves).

However, there is good news on the horizon for this group of bats. Researchers from the U.S.D.A. Forest Service, the University of Georgia and Bat Conservation International recently tested a common North American bacterium that inhibits fungal growth on a group of 75 little brown bats in Missouri that were exposed to White Nose Syndrome.

These bats were found to be free of the fungus and were released back into the wild this past spring. While there are no guarantees these bats will not contract the disease again (and killing the fungus left on cave walls also remains an issue), the fact that there is a potential treatment offers a glimmer of hope. In addition, wintering cave bat mortality rates in Pennsylvania, New York and Vermont appear to be dropping off, with residual populations of hibernating cave bats now small, but holding steady.

This may indicate either resistance to the disease or an ability to live with it without severe impact. Researchers in New York and Vermont put radio transmitters on 450 little brown bats last year to track their movement (and survival rate) and there are bats that were banded in Vermont in 2006 (pre-White Nose Syndrome) that are still alive. With further research, the glimmer of hope for our cave bats may just start to.

Wind Farms

There is increasing evidence that wind turbines kill tree bats during the breeding season and migration. Bats are attracted to slow moving wind turbine blades, but no one is sure why. Three migratory species – the hoary bat, the Eastern red bat and the silver-haired bat – make up the majority of bat species killed each year at wind farms across the country.

New wind developments can pose a threat to tree bats, but Maine has developed strong guidelines that significantly reduce bat mortality by stopping the blades from spinning at low wind speeds, the time when bats are inexplicably attracted and most often killed at turbines. Studies have shown reductions of up to 40-80% of bat mortality when “curtailment” is in place and MDIFW’s strong curtailment guidelines have been a condition of wind permitting over the last several years in Maine.

Monitoring Efforts

One of the barriers to helping bats in Maine is that we don’t know much about where they are or what they do. Two new state initiatives will help shed light on this mystery. The North American Bat Monitoring Program (NABat) is a national monitoring project that uses acoustic recorders in established areas (both stationary and on driving routes) to record bat activity over several days. Maine Audubon citizen science volunteers recently helped the Maine Department of Inland Fisheries and Wildlife with two of these locations in southern Maine.

The other exciting initiative has trained 16 citizen scientists in southern Maine to use a small acoustic device attached to an iPad to record bat calls in real time. The device shows the bat calls on the screen and translates them to a frequency we can hear. Though only a pilot project this year, project director Eric Blomberg from the University of Maine is hoping to expand the project next year to more volunteers across a greater geographic reach of the state. Maine Audubon citizen scientists have been crucial to the testing of the device this summer, with over 2,000 bat calls recorded in just two weeks of testing!