By Michele S. Byers
Sit outside on a summer evening around sunset and look up. If you are in an open area with nearby woods, you may be treated to a dazzling aerial display of bats hunting for flying insects.
“They are endlessly fascinating,” said Ethan Gilardi, a bat biologist with the nonprofit Conserve Wildlife Foundation of New Jersey. “They are fun fliers, with all their diving and weaving and hairpin turns.”
Besides being interesting to watch, bats provide priceless insect control services in a state that jokingly refers to the mosquito as its state bird.
“A single little brown bat can eat 3,000 insects a night,” noted Ethan. “They eat every kind of insect pest you can think of.”
But many of New Jersey’s bats are struggling to survive. Fifteen years ago, a fungus attacked hibernating bats, leading to a disease known as white-nose syndrome.
The disease disrupts hibernation, causing bats to use up their vital energy needed to survive the winter. White-nose wiped out most of the bats in the Myotis genus: little brown bats – once our most widespread species – and northern long-eared bats.
New Jersey has six year-round bat species that hibernate in caves, abandoned mines and other structures. In addition to little brown and northern long-eared bats, this state we’re in is home to big brown, eastern small-footed, tri-colored, and Indiana bats.
Big brown bats seem to be the least affected by white-nose and in recent years have become New Jersey’s most commonly seen bat. New Jersey bats that migrate south for the winter include hoary, eastern red and silver-haired bats.
In the years since the white-nose fungus emerged, biologists have been monitoring all bats – especially the surviving little brown and northern long-eared bats – to find out how healthy they are, if they are successfully reproducing and how humans can help.
Right now, it’s too early to tell if bat populations are rebounding. Breeding females usually give birth to only one pup a year, so it will take many years for their colonies to rebuild.
“At least in New Jersey, affected populations have bottomed out,” said Ethan. “It’s going to take some time to see if those numbers are going to trend upward.”
Researchers believe little brown and northern long-eared bats may be adapting to white-nose. For instance, because the fungus exists in cold and moist conditions, some bats that chose to hibernate in slightly warmer and drier areas of caves and mines may have survived the initial onslaught of the disease.
A tiny fraction of individuals may also have been fortunate to have had some heritable genetic traits that allowed for slightly better survival and reproduction. So there is hope. From the remaining small populations, genetic resistance to the disease might be passed on to future generations.
In New Jersey and throughout North America, scientists document bat populations using acoustic surveys, maternity colony counts, winter hibernaculum counts and other methods. It’s not easy work. Bats are notoriously tricky to study, since they are small, reclusive and nocturnal.
Summer is a busy time for bat researchers like Ethan, who specializes in acoustic monitoring for the Conserve Wildlife Foundation and the state’s Endangered and Nongame Species Program.
Bats navigate and find insect prey using “echolocation.” They produce sound waves at frequencies humans can’t hear and these sound waves bounce off objects to let bats know where they are. These acoustic waves can be recorded and analyzed by a computer program to determine which bat species made the calls.
Ethan spends many summer nights driving pre-selected routes on New Jersey back roads with recording equipment – which he calls the “bat detector” – strapped to his car.
“You have to drive at 15 mph or less,” he said. “It’s surprisingly difficult.”
He also sets up stationary recording sites with bat detectors attached to trees and tall poles.
On summer nights, researchers also use fine-gauge nets known as “mist nets” to capture bats in flight at selected sites. Bats are identified by species, weighed and measured.
Little brown and northern long-eared bats are checked for scarring on their wings and other signs of white-nose infection. Before being released, they are banded and sometimes outfitted with a microchip that allows researchers to track them for up to two weeks.
Researchers might, for example, use the tracker to learn where a lactating female bat is roosting and how her pup is doing. If a bat roost or maternity colony is discovered on land that is not protected, the data could be cited as a reason to conserve the land.
“We want as much habitat as possible for all our bats,” explained Ethan.
Though some people fear bats – concerned about rabies or other diseases – most bats do not carry rabies and are not interested in contact with humans. If bats are living near your house, swooping and diving for insects on a warm summer night, consider yourself lucky. Try putting up a bat house to attract more to your property.
Although white-nose has been devastating, it could have been worse, according to Dr. Emile DeVito, the New Jersey Conservation Foundation’s staff biologist.
Because so much forest in New Jersey has been conserved during the last century and water quality has improved, he explained, there is plenty of habitat for bats’ insect prey.
“Bat populations were large and healthy when white-nose syndrome first hit. Although millions of bats perished, there was still an abundance of genetic and behavioral variability available as raw materials for natural selection,” Emile said.
He noted that if another new disease were to be introduced now, while bat populations are extremely low, the chance that a species could survive would be virtually nil.
“And the omnipresent problem of crashing insect populations due to dangerous neonicotinoids and other pesticide overuse may be inhibiting a bat comeback,” added Emile.
Michele S. Byers is the executive director of the New Jersey Conservation Foundation, Far Hills.