Bats are a fascinating, adaptable, and widespread group of animals, not to mention one of the most beneficial to people. Bats make up nearly a quarter of all mammals on earth, both in species diversity and sheer numbers. New Jersey is home to nine different species of bats, and whether you live on a farm, in the forest, along the shore or in a city, bats are most certainly close by.
A Year in the Life
During the warm months, bats roost by day in narrow nooks and crevices where other animals won't see or can't reach. Many live inside tree cavities, beneath loose bark, or tucked behind shutters or in the attic of a house. Red bats (Lasiurus borealis) and Hoary bats (Lasiurus cinereus) roost in the canopy of trees and shrubs, just dangling among the leaves for camouflage. Eastern small-footed bats (Myotis leibii) roost mainly in rock crevices within talus areas and cliffs.
Female bats often group into large colonies in the spring and summer to share safe, warm spaces where they can raise their pups. These "maternity colonies" can number in the tens, hundreds, or sometimes thousands of bats, though it's rare to find those really large colonies since the onset of White-nose Syndrome (read on). Most mother bats give birth to just one pup each spring, in May or June, and nurse for about a month until that pup can fly and feed on its own. A bat colony will use the same familiar roosts year after year.
Bats are active outside the roost at night, of course. Stare overhead for a while at dusk and there's a good chance you'll see one, flapping and swooping in manic patterns. They spend the night foraging on insects - consuming at least half their own body weight worth of bugs each night and twice that amount when they're pregnant or nursing (that's equivalent to more than 3,000 mosquito-sized insects per night). A recent study published in Science magazine estimates the value of bats' insect-eating services at between $3.7 billion and $53 billion per year to U.S. agriculture by preventing crop damage and reducing the need for pesticides (Boyle et al. 2011).
Bats navigate the night skies by echolocation, where their high-frequency vocalizations bounce off objects around them and return to their ears as echoes. Their calls are above the range of human hearing, but in this video an acoustic detector "translates" the sound of a bat overhead.
As winter approaches, temperatures drop and insects dwindle. A few of New Jersey's bat species migrate south to warmer climates, but most seek refuge in-state (or in surrounding states) for hibernation. Many of our abandoned mines, natural caves, and defunct railroad tunnels offer the right above-freezing temperatures, humidity and solitude that bats require to ride out the winter below ground. A significant drop in heart rate, metabolism, and body temperature allow bats to conserve energy and survive for several months without food until spring returns.
An Eastern Red Bat roosts in a shrub. Photo courtesy of Kristina Necovska
More than 200 Big Brown Bats share this church attic roost every summer.
From beneath the loose siding of a barn, a Big Brown Bat dives into the night.
Little Brown Bats speckle the ceiling of a mine in Hunterdon County, passing the cold winter months below ground.