CSI: Seahorse Key

When birds suddenly up and abandon their nests by the thousands, who or what is to blame?

Photo: Justin Warner/Flickr

At this time of year, the largest colony of nesting birds on Florida’s Gulf Coast is usually squawking up a storm on Seahorse Key. Thousands of egrets, ibises, pelicans, cormorants, and other species come to this strip of sand and mangroves to raise their chicks. Or they did, until one day this April when all of a sudden—*Detective Caruso puts on sunglasses*the birds flew the coop.

“It’s completely empty,” says wetland ecologist Peter Frederick, “and silent.”

Leaving their nests behind—eggs and all—the birds just up and left like daddy going out for a pack of cigarettes. It’s what Andrew Gude, manager of the Cedar Keys National Wildlife Refuge, calls “catastrophic nesting-island abandonment.”

While ditching a nesting site can be relatively common, the fact that it was so many birds of various species doing it at once is very peculiar. And as far as anyone can remember, it’s never happened at Seahorse Key. 

Frederick—a professor at the University of Florida, which maintains a marine laboratory on the key—has studied the island’s birds for nearly three decades. Whatever is happening (or happened) on Seahorse Key, which from above looks like the grin of a jack-o’-lantern on bath salts, affected as many as nine types of birds, all with their own sets of behaviors, food preferences, and foraging strategies.

So what might make 15,000 birds vanish unexpectedly from a tried-and-true nesting ground like a muggle happening upon a portkey? Let’s explore the possibilities.

This weather is the pits.

In the nearby Everglades, when unseasonable rains flood channels and send prey species far and wide, scientists will occasionally see two to three bird species simultaneously leave a nesting site. Similarly, there’s evidence that seabirds in the Galapagos will cut and run when currents shift or El Niño rears its ugly head

And there were reports of heavy storms in the area around the time of the disappearance, but big rainstorms off the Florida coast in April are hardly uncommon.

Something they ate?

“If all the food sources, which range from 40 miles inland to 20 miles offshore, were to go south at once,” says Frederick, “we’d see some bigger problems happening.”

Furthermore, refuge workers have found nests indicating that many of the birds have relocated to Snake Key, about a mile and a half away. Gude says they also just recorded the first-known occurrence of frigate birds there, so conditions there must be cozy. This suggests that the problem may be specific to Seahorse.

Hungry neighbors…

“There’s no conclusive evidence of anything except that we know we caught some raccoons,” says Gude.

At 45 miles offshore, Seahorse Key is inaccessible to most predators, but it is not impenetrable to raccoons, which frequently make the swim, either by dumb luck or because of an extreme hankering for eggs Benedict.

Raccoons are known predators of bird’s eggs, and Gude says refuge workers trapped out half a dozen of the masked bandits, one of them a lactating female, around the time of the abandonment. But this, too, is not all that unusual.

The island’s cottonmouth snakes are also not known to attack birds so we can’t blame them.

…Or noisy neighbors.

Pathology results from the handful of carcasses found on Seahorse were inconclusive, so disease isn’t a suspect. Likewise, forensics showed no signs of gunshot wounds. This leaves one probable suspect: us.

“My best guess right now,” says Frederick, “is this was some sort of catastrophic disturbance that could have stemmed from human activity.”

Homeland Security, the U.S. Department of Defense, and the Drug Enforcement Administration routinely patrol Florida’s coast. With helicopters, boats, and searchlights, they’re looking for everything from illegal immigrants to drug traffickers to terrorists. So it’s possible some fly-over disturbance could have ruffled a few feathers. Still, Frederick thinks it would take a helicopter hovering over the island with floodlights shining all night long to send that many birds packing.

Displacement by a thousand cuts.

Perhaps the more likely scenario is far less neat and tidy. Frederick says there may not be a single explanation but rather a cumulative effect of many things going wrong at once.

Maybe the storms and flyovers riled the birds up, and the arrival of the raccoons put them over the edge? We may never know, but whatever the cause, the event, says Frederick, is a talisman of the problems facing island-nesting birds everywhere.  “The number of island colonies nationwide is actually shrinking pretty fast,” he says.

Pick an island or coastal area and you’ll find a scientific study warning about the threat sea-level rise poses to birds: Hawaii, the Chesepeake Bay, Canada’s Barrier Islands, Louisiana. Human development and oil spills also make islands less hospitable for nesting birds. (Just take a look at what the BP disaster did to Louisiana’s Cat Island!) And where humans go, populations of nest raiders like rats, raccoons, foxes, and opossums tend to follow.

The birds that fled Seahorse Key are protected by the Migratory Bird Treaty Act, and some, such as the roseate spoonbill (state-designated threatened) and reddish egret (state species of special concern), require additional protections. So Gude says the U.S. Fish and Wildlife Service plans to sit down with other government agencies (such as those patrolling Florida’s shores) before the next nesting season in order to make sure proper policies are in place to not disturb wildlife.

For spoonbills and cormorants to play musical chairs with their nesting sites is somewhat natural, and being flexible when conditions get rough is good for a species’ chances of survival.

But as the waters rise, it’s also up to us to find ways to reduce our own impact on island ecosystems, lest the birds have nowhere to go the next time the music stops. 


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