On a typical summer day, Florida's Seahorse Key is a hub of bird activity, with numerous species settling there for the warmer months.

 

This year, however, is different. In late spring, all of them vacated the area swiftly and at the same time, leaving behind empty nests and broken eggs.

 

Officials have no explanation for the birds' departure.

 

They've performed a number of tests to rule out disease and predators, but human activity is still considered a possibility.

 

Seahorse Key has been a popular spot among blue herons, snowy egrets, pelicans and many others for decades. In 1929, it was established as a protected refuge for them.

 

Keeping masses of people away hasn't proven to be too hard, as the place is teeming with mosquitoes, yellow flies, and cottonmouth snakes.

 

While such creatures can be both dangerous and annoying, the birds found a way to work with them and develop an environment in which all inhabitants thrived.

 

That's part of what makes the avian exodus so puzzling.

 

Experts are having a tough time imagining what could have occurred to make the birds leave a home they spent so many years establishing.

 

 

PHOTO: In this Friday, June 19, 2015 photo, an Osprey returns to its nest in Seahorse Key, off Florida’s Gulf Coast. In May, Seahorse Key fell eerily quiet, as thousands of birds suddenly disappeared, and biologists are trying to find the reason why. U.S. Fish and Wildlife Service biologist Vic Doig said what was once the largest bird colony on the state’s Gulf Coast is now a dead zone.

CREDIT: AP Photo/John Raoux.