From Massachusetts to Maine, beautiful seabirds are mysteriously dying.
Since April, more than 100 northern gannets have been reported sick and dozens have died.
"The troubling part is no one has been able to definitively point to a root cause," said Zak Mertz, executive director of the Cape Wildlife Center in Barnstable, Massachusetts.
Mertz said in the last eight weeks his center has taken in about 10 northern gannets exhibiting signs of neurological problems, tremors and gastrointestinal distress.
"Gannets are very hearty seabirds, and these birds that are coming in to us ... they've contracted something, and they're perishing soon after," he said.
Scientists are calling it a sudden and unexplained die-off. Veterinarians are taking tissue samples of the birds, and sending them to labs to get answers.
"It's unusual for us to see such a massive die-off event," said Derek Lovitch, an avid birder, author of "Birdwatching in Maine: A Site Guide," and owner of the Freeport Wild Bird Supply.
"Gannets are pretty high up in the food chain, and something going on with them is usually a sign that there's something going on below," Lovitch said.
Scientists have different theories. The prevailing thought is that it's a toxic algal bloom that's killing the birds. Harmful algae can grow when ocean temperatures rise.
Another possibility is a virus.
Diana Dumais, wildlife specialist at the Center for Wildlife in Cape Neddick, Maine, said her facility has taken in two sick gannets this spring. They did not appear to have parasites, anemia or high lead levels in their blood.
New England wildlife centers have sent samples to labs throughout the region and expect test results in the coming weeks.