I WAS ON THE PHONE with a fellow gardener last week near dusk when the first bat I’d seen this spring flew right past the window. “A bat,” I said excitedly to my friend, who quickly replied, “So many are dying—have you read about it?” I hadn’t, but now I have: Today the point hit home even more clearly, when during my first round of cleanup in the garden I found a bat carcass, desiccated but intact, among the leaves. The cause of a mysterious disease that is killing thousands of hibernating bats and sharply reducing populations in New York and Vermont is unknown, but under investigation, the New York State Department of Environmental Conservation reports.

May 31 update: In a lecture at the Harvard Museum of Natural History on May 21, a Massachusetts endangered species expert confirmed that the reason for the deaths, put at 250,000 to 500,000 bats already, remains unknown.