Bat Mortality in Massachusetts

Like much of the United States, Massachusetts has experienced a drastic mortality of bats.

White-nose Syndrome (WNS) is the descriptive term given to a condition first observed in bats hibernating in a cave near Albany, NY in February 2006. The term comes from the fact that some of the bats with this condition look like they dipped their faces in powdered sugar. The white powdery substance on their faces is a fungus. On closer examination, this white fungus can also be seen on the bare skin of their ears and wings. In 2009, this fungus was described as a newly discovered species and named Geomyces destructans to highlight the harm that it is causing to North American bats. The fungus is now known as Pseudogymnoascus destructans, or Pd. This fungus grows best in cool temperatures and high humidity, similar to the conditions found in bat winter hibernation sites, like caves.  

Little Brown Bat with White-nose Syndrome.
Little Brown Bat with White-nose Syndrome. Photo by Bill Byrne, MassWildlife

Ordinarily, bats that hibernate over the winter have enough fat to last them until they emerge in late April and early May. In the spring, there are ample numbers of insects to eat so the bats can replenish their energy reserves. However, at caves and mines with WNS, some of the hibernating bats use up their precious fat reserves by early February. They can be seen flying outside in the daytime in a desperate attempt to find something to eat. This is because the fungus rouses the bats and increases their metabolism. The fungus also irritates their skin, creating holes in the wings of bats leading to dehydration. Unfortunately, any bat that runs out of stored body fat too early or leaves its hibernation site when nighttime temperatures are still below freezing, ultimately starves to death.

At the largest Massachusetts bat hibernation site in a mine in Chester, there were about 10,000 bats in early winter 2007/08. By the end of winter 2008/09, nearly every bat had been killed by WNS and only 14 bats remained.

DFW staff examine bat hibernacula.
DFW staff examine bat hibernacula.

White-nose Syndrome continues to spread rapidly and has caused a catastrophic mortality of bats that spend the winter in caves and mines. By 2009, nearly half a million bats had died from WNS in the northeastern states from Vermont south to Virginia. By 2013, over 2 million bats had died at sites from eastern Canada, south to Alabama, and west to Oklahoma. As of 2017, WNS has been confirmed in 31 states and 5 Canadian provinces, and the disease is estimated to have killed over 6 million bats. At this point, no one knows how to stop or even slow the continuing spread of WNS. No one can predict just how far it will eventually go and how many bats will die in the process.

As a result of the devastating mortality that has resulted from WNS in Massachusetts, all 4 of our bat species that spend the winters in caves or mines have been listed as Endangered. This includes the Little Brown Bat, which used to be the most abundant species of bat in Massachusetts. The other species are the Northern Long-eared Bat, Eastern Small-footed Bat, and Tricolored Bat (formerly known as the Eastern Pipistrelle). The Indiana Bat was already listed as Endangered as a result of impacts from the pesticide DDT, and was last seen in the Chester mine in 1939. The only 2 Massachusetts bats that have summer colonies in houses are the Little Brown Bat and the Big Brown Bat. Most of the Little Brown Bat colonies are now gone, but Big Brown Bats have not been seriously affected because most hibernate in cold, dry attics where Pd does not grow. The few Big Brown Bats that did hibernate in cold, wet caves and mines have already died. There are also 3 species of tree bats in Massachusetts that migrate south for the winter. These bats, the Eastern Red Bat, Hoary Bat, and Silver-haired Bat, are not exposed to the WNS fungus.

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