By now, "every bat left in the landscape is precious," Bucknell University researcher DeeAnn Reeder said.
You can help the bats by giving them summer homes. And you can help the researchers by joining a summer bat count.
Bats are emerging from hibernation now, and they'll be looking for places to gather in "maternity colonies" to have their young.
Usually, this is a barn, church steeple, abandoned house, or some other building. Even a tree.
But buildings get torn down. Trees fall over.
So putting up a bat house - the bat version of a bird nesting box - is one of the things that can be done to reduce stress on the bats in summer, said wildlife biologist Cal Butchkoski, one of the Pennsylvania Game Commission's true bat men.
Generally, bat houses are thinner than a bird's nesting box, because bats like tight places. The idea is to mimic the space between a tree trunk and its bark, according to Bat Conservation International, an advocacy and educational group in Texas.
Best of all, helping bats will help you, too. The little guys devour massive quantities of insects, including mosquitoes. According to the New Jersey Department of Environmental Protection, a single bat can eat half of its body weight each night - up to 3,000 insects an hour.
"Before white-nose hit, I had 1,030 bats in two large bat boxes in my back yard," said Butchkoski, who lives in Huntingdon County, west of Harrisburg. "And I could sit out back at dusk and enjoy the evening."
In 2010, the population dropped to 400. The next year, they were all gone.
"In 2012, I put in a fire pit and things to make smoke" to try to control insects, he said.
Those with gardens also can benefit from bats, because they eat cucumber beetles. The DEP says 150 big brown bats can eat enough cucumber beetles each summer to protect farmers from 18 million of the beetles' larvae. This is important because controlling the larvae costs close to $1 billion annually.
Topping it all off, many garden pests can somehow detect the feeding sounds bats make, and they skedaddle. So, without bats, the DEP says, we would be more dependent on toxic pesticides to control insects.
Another way people can help is to join an annual bat count, which helps biologists determine how bat populations in a given area are faring from year to year. Pennsylvania and New Jersey have bat counts.
The idea is that you stand outside a known bat site at dusk and count the bats as they emerge. The count is done in June, and again later in the summer, when the pups begin flying - so you can see how the colony has grown.
"We're not going to give up hope," Butchkoski said.
Here are bat-house tips from Butchkoski and others:
The house should be at least 10 feet above the ground, but not over a window or some other place where you wouldn't want droppings.
The house should get sun most of the day; bats like temperatures between 85 and 100 degrees.
Avoid areas with trees, which might be shady and might have hawks or owls in residence.
Bats like water, so make sure the house is within about a quarter-mile of a stream, pond or river.
Even if you want to buy a bat house instead of making one, check out some of the building plans so you know what to look for. Not all manufactured houses are adequate, Butchkoski said.
If you don't get bats in the spring, be patient. It's common for bats to roost somewhere else, but to begin checking out alternatives for next year late in summer.
Information About Bats
The Pennsylvania Game Commission has materials on bats, bat houses, and the summer count. Go to www.pgc.state.us , click on "wildlife," then click on "wildlife" again, then "Appalachian bats."
In New Jersey, the Department of Environmental Protection covers bats. www.njfishandwildlife.com/ensp/bat.htm
Conserve Wildlife Foundation of New Jersey has information and sponsors an annual bat count. www.conservewildlifenj.org
Bat Conservation International has cool bat facts, bat-house plans, even bat poems. Also lists makers of bat houses it has certified. www.batcon.org
Habitat for Bats sells bat houses. www.habitatforbats.org
Bats Live, a Virginia site sponsored by bat and wildlife groups. http://batslive.pwnet.org
"GreenSpace" appears every other week, alternating with Art Carey's "Well Being" column. Contact staff writer Sandy Bauers at 215-854-5147, email@example.com, or follow @sbauers on Twitter. Visit her blog at www.philly.com/greenspace.