DEEP: Big brown bat seen most often in state

The big brown bat has been determined to be the most frequently seen species of bat in Connecticut after other types have declined because of whitenose syndrome, officials said.

The little brown and big brown bats were the most common bat species found in the state until white-nose syndrome was documented in Connecticut, beginning in 2008, according to the state Department of Energy and Environmental Protection.

Several bat populations in the state have been devastated by white-nose syndrome, DEEP said. Those species most impacted — known as “cave bats” — have dropped population totals so dramatically that they were added to the state’s list of endangered, threatened and special concern species in 2015.

The big brown bat and little brown bat are both classified by the state as needing the “greatest conservation efforts.” The little brown bat is also labeled as endangered in Connecticut.

White-nose syndrome hits cave-roosting bat species the hardest, causing extensive mortality in hibernating bats across eastern and midwestern parts of the country.

In 2012, the U.S. Fish and Wildlife Service estimated that about 5.7 million to 6.7 million bats had died in the eastern U.S. and Canada since white-nose syndrome was discovered in New York in 2006.

The mortality rate has reached 90 to 100 percent in some species. DEEP said in Connecticut, the northern long-eared bat, little brown bat and tri-colored bat populations have seen the greatest declines. The agency said the big brown bat and eastern small-footed bat have also seen population declines due to white-nose syndrome, but those losses have not been as severe.

Researchers studying white-nose syndrome determined it is caused by a fungus that is visible as a white, powdery growth on the skin and muzzle of hibernating bats. DEEP said the fungus thrives in cold, humid conditions — typical for caves and mines used by bats for hibernation.

White-nose syndrome is transmitted primarily from bat to bat, especially where they gather in clusters. People can inadvertently carry fungal spores from cave to cave on their gear and clothing, DEEP said.

The fungus infects the muzzle and wings of bats when their metabolism and immune systems are essentially shut down. Bats infected with the fungus wake up more frequently from hibernation and burn much-needed fat reserves. Once energy is depleted, it’s unlikely the bat will survive the winter. DEEP said some bats who lose their energy can be seen desperately searching for food and water, only to die from lack of food and exposure.

Biologists with the Wildlife Division of DEEP continue to monitor hibernating bats for signs of whitenose syndrome and track summer maternity colonies.