DAVID GREENE, HOST:
Let's try to solve a mystery along the Gulf Coast of Florida. We're going to Seahorse Key, an island off the coast, a hundred or so miles north of Tampa. It was known for decades as a breeding area for birds. Tens of thousands lived there - until they all disappeared. Here's Amy Green from member station WMFE.
AMY GREEN, BYLINE: Seahorse Key is accessible only by boat. It's a snake-and-mosquito-infested thicket of mangrove, palmetto and oak trees. And it used to remind Larry Woodward of Christmas.
LARRY WOODWARD: When they were nesting here, these mangroves along the edge just looked like Christmas trees, just full of birds all hanging on the edge. And of course a lot of the nests would be on the edge as well, primarily the pelicans but the egrets as well.
GREEN: Woodward works at the Lower Suwannee and Cedar Keys National Wildlife Refuge, which includes Seahorse Key. We're motoring near Gardner's Point, the part of Seahorse Key where most of the birds nested.
It doesn't look like Christmas now.
WOODWARD: (Laughter) It's very green. The vegetation's here but minus the birds. So hopefully next year, it'll be Christmas.
GREEN: Here, the island would have been teaming with chattering birds raising young that would've only begun learning to fly. We bring the boat ashore and hike a few steps into a clearing, watching for snakes.
I'm going to follow you 'cause the trail's not very apparent.
We're greeted by silence.
KENNY MCCAIN: It happened within a three-day period that I know. They were there on the 19. They were gone on the 21.
GREEN: Kenny McCain is retired from the U.S. Fish and Wildlife Service and now serves as a steward of the island. He discovered the bird's disappearance in April.
MCCAIN: It just gave you that eerie feeling of - what? - like something has come in and just sucked everything off the island because it was quiet.
GREEN: Birds had left behind thousands of nests filled with a generation of eggs. Researchers began looking for clues. They tested a few bird carcasses found on the island, ruling out disease. They discovered no evidence of predators or human influence. A storm had moved through at the time of the disappearance, but storms here are frequent. Some species are nomadic, like ibis, but researchers don't know why all the birds abandoned Seahorse Key. Maria Sgambati is part of the University of Florida's Seahorse Key Marine Laboratory, which is based on the island.
MARIA SGAMBATI: It would be an unusual thing for birds to abandon nests where they had laid eggs. So I think we clearly think there was some sort of disturbance. I mean, that's a pretty high-energy event for - to build a nest for a bird, to lay eggs. So that, I mean, it consumes a lot of their energy.
GREEN: Researchers also don't know where the birds went. They searched the region by air but only can account for a small fraction of the birds. Some of them renested on nearby Snake Key. Here the mangroves and palmettos are like Christmas trees, adorned with pelicans, cormorants and frigatebirds raising their young.
So how does this compare to what would have been going on on Seahorse Key this time last year?
WOODWARD: This would be real similar but in a larger scale.
GREEN: Researchers want to know what happened to the birds on Seahorse Key because they don't want it to happen elsewhere. What worries Woodward is that birds tend to nest in the same place each year, and so if they don't return to Seahorse Key, a significant rookery could be lost.
WOODWARD: For all those birds to just up and leave is pretty shocking. So it's - that's why we're here, to protect these birds. And, luckily, we have them on Snake Key. We just really hope they come back next year. And we're going to be crossing our fingers and looking at the horizon come February, and hopefully, they show up.
GREEN: The first to arrive would be ibis and egrets. For NPR News, I'm Amy Green. Transcript provided by NPR, Copyright NPR.