Because of steep population declines over many decades, this sensitive species is considered endangered throughout its entire midwest-to-eastern US range.
The Indiana bat (Myotis sodalis) is one of nine bat species found in New Jersey. It is our state’s only endangered bat and was among the first animals to be listed under the US Endangered and Nongame Species Act (1973). Because of steep population declines over many decades, this sensitive species is considered endangered throughout its entire midwest-to-eastern US range.
The Indiana bat measures just two inches from head to rump, has a ten-inch wingspan, and at eight grams, weighs a little more than a quarter. The Indiana bat closely resembles its relatives in the Myotis genus, especially the little brown bat (M. lucifugus). Biologists look for key features as subtle as toe hair length and the hue of a bat’s fur in order to tell these species apart.
Like all NJ bats, Indiana bats are eager insect-eaters that can consume more than half their body weight in moths, beetles, flies, mosquitoes, and other flying bugs each night from spring through fall. They have fine vision (probably as good as ours) but rely on echolocation to navigate and catch prey in the darkness of night, typically along floodplains and above the tree canopy.
In the daytime, while male Indiana bats roost alone or in loose bachelor colonies, females group together in maternity colonies of up to one hundred or more adults. What they’re after is not companionship – so far as we know – but rather a safe, dry, and warm environment for raising their young. Each female will give birth to just one pup per year and will nurse it for a month. Indiana bats tend to choose dead or dying trees in sunny locations, roosting snugly under sheets of flaking bark.
Indiana bats don’t stay put, though. Radio-telemetry studies, including one within Great Swamp National Wildlife Refuge, have found that maternity colonies switch roosts often, sometimes nightly, even when the pups are young and flightless. This strategy probably deters parasites and predators, allows for thermoregulation, and keeps the bats on their toes, since dead trees do not stand forever. It also underscores the value of balanced, multi-aged forests.
In early fall, all of NJ’s bats make some kind of move to prepare for winter. Three species – the red, silver-haired, and hoary bats – migrate to southern states, while six “resident” species make a shorter jaunt to their familiar cave, mine, or other hibernation spot. Indiana bats use only caves that meet their preferences for temperature (3-6°C), humidity (87%), dimension, and air flow. Very few caves and mines fit the bill, so those that do contain nearly all of the Indiana bats in existence.
Disturbances during hibernation can literally cost the bats their lives.
It is this selectivity that makes the Indiana bat most vulnerable. During hibernation, bats drop into a low metabolic state and won’t eat again until spring. They awaken on their own periodically, but unscheduled arousals can cost them weeks or even months worth of stored energy. Disturbances during hibernation can literally cost the bats their lives. In the late 1960s, for instance, repeated cave exploration in Virginia’s Rocky Hollow Cave may have reduced an Indiana bat population from more than one million bats to mere thousands in a single year. New Jersey’s own Hibernia Mine – the largest known bat hibernaculum in the state – was under similar threat until it was gated and preserved in 1994.
The latest threat to Indiana bats and other cave species is quickly unraveling years of conservation work. White-nose Syndrome (WNS) has spread to at least a dozen states and two Canadian provinces in the past four winters. WNS upsets the bats’ hibernation cycle, depleting their energy stores and causing starvation. Nearly all bats have died at many affected sites.
We are participating in several research projects looking into the causes of WNS, its means of spreading, and possible treatments or solutions. Please visit our website to learn more about WNS and related research.
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