Only a couple of dozen bats spent this past winter in New Hampshire.
That’s down from thousands a decade ago, before a fungus called white nose syndrome decimated many species’ populations in 2009.
Biologist Scott Reynolds says since then, the mine shafts where bats used to hibernate in large numbers have been pretty empty.
But white nose has also subsided in New Hampshire.
Now, Reynolds says recovery for the species hit hardest, such as little brown bats, is just beginning.
"Because they have one pup per year, literally, it'll take probably close to a century for them to get back to the numbers they were at pre-white nose,” he says.
He says the lack of hibernating bats in New Hampshire probably reflects how overall, year-round Northeast populations have dropped.
Most that did winter here are big brown bats, a common urban species that was relatively less affected by white nose.
On the other hand, only one little brown bat – once the most common Northeast species, with more than 3,000 hibernating in New Hampshire – was found in winter surveys this year.
But Reynolds says that doesn’t mean only one little brown bat will ever visit the Granite State again. Plenty more bats of all species still migrate back from Vermont and New York in the summer.
"Even at our best, when we were doing surveys at every site we knew of for the winter, our total count was about 6,000 bats," he says. "That's not even a small fraction of the total bats in New Hampshire during the summer."
He says this latest data shows that winter surveys probably won't be useful in New Hampshire in the future, because so few surviving bats remember hibernating in the state's abandoned mines.
"If there's no bat that's alive that's ever been to the site, then I don't understand how new bats would find it," Reynolds says. "If they're empty, how is a bat going to find a little 4-foot-by-3-foot hole in the ground in the middle of the forest on the side of a hill in Northern New Hampshire?"
It means researchers will have to rely more heavily on summer population data, which residents can help collect by counting bats in their homes and barns this year.