By Michele S. Byers
As temperatures cool and daylight hours shorten, New Jersey’s non-migrating bats have gone into hibernation.
For the last decade, hibernation for New Jersey’s bats has been unusually precarious. A disease known as white-nose syndrome – caused by a fungus – has decimated many bat species by scarring their wings and disrupting hibernation patterns, causing them to wake and fly around when they should be sleeping. After depleting their energy reserves, the bats die from starvation, thirst and exhaustion.
The little brown bat is most affected. This once common bat has now lost nearly 99 percent of its population. In 2007, before white-nose syndrome struck, the state’s largest bat cave (or hibernaculum) – the old Hibernia Mine in Morris County – was the winter home for 34,000 little brown bats. Today, the number is down to about 400.
But there may be hope. The devastating losses appear to be leveling off. MacKenzie Hall, a biologist with the state’s Endangered and Nongame Species Program, said the year-to-year survival rate for little brown bats is almost back to normal.
“They are still not growing in number, but they are almost leveling,” she said.
Scientific understanding of white-nose syndrome is expanding, due in part to the contrast between the plight of little brown bats and the success of another New Jersey species, big brown bats.
Big brown bat numbers are growing and they seem unaffected by white-nose syndrome.
Why? One difference between big browns and little browns is where they hibernate. Many big brown bats hibernate in cold, dry attics instead of in caves, reducing their exposure to the warmer temperatures and higher humidity found inside caves and abandoned mines. Big browns that do hibernate in caves stay closer to entrances, where the temperature is cooler.
According to Hall, laboratory studies have shown that the white-nose fungus grows best between 41 and 50 degrees. These temperatures are found deep in caves where little brown bats hang out. The fungus does not grow as well below 41 degrees.
Recently, Hall said, the state removed part of an old concrete wall that blocked air flow into the Hibernia Mine. This may drop temperatures slightly, inhibiting the growth of white-nose fungus in places where little brown bats hibernate.
Big brown bats also have different feeding habits. Hall said researchers from Fordham University found that the wings of big browns have a buildup of fatty acids, most likely from the type of insects they eat. These acids appear to prevent the fungus from growing and damaging fragile wing membranes.
“It could just be a fluke of nature, these small differences in diet,” Hall noted.
Genetics may also help bats survive white-nose syndrome, according to a study by Rutgers University researchers, who are working in cooperation with the Endangered and Nongame Species Program. The 1 percent of little brown bats that survive white-nose syndrome seems to be passing immunity on to their offspring.
This winter, biologists will carefully monitor bat caves in New Jersey and look for signs of improvement for little brown bats and other species affected by white-nose syndrome: northern long-eared bats, tri-colored bats and eastern small-footed bats. All four have been recommended for inclusion on the state’s endangered species list.
“There has been a pretty helpless feeling in the last eight to 10 years,” Hall said. “But if there is any silver lining, it’s that people are appreciating bats a lot more.”
Bats are our only flying mammals and they are hugely beneficial. Bats are the single largest consumer of night-flying insects – including mosquitos, beetles and moths – and the value of this natural insect control to agriculture in the United States is estimated at $22.9 billion per year.
Want to help bats in your neighborhood? Install a bat house for summer maternity colonies. Leave some dead or dying trees standing so bats can roost behind the loose bark.
If you discover bats in your attic or home, do not try to remove them on your own. Call a bat removal expert who will safely “exclude” them. The Conserve Wildlife Foundation of New Jersey and Rutgers provide free bat houses to those who evict bats safely.
For more information about New Jersey’s bats, go to the Rutgers website at http://wildlife.rutgers.edu/bats/ or the Conserve Wildlife Foundation website at http://www.conservewildlifenj.org/protecting/projects/bat/white-nose/
Another great resource is Bat Conservation International at www.batcon.org
Michele S. Byers is the executive director of the New Jersey Conservation Foundation, Far Hills.