What do you do when one of your natural treasures starts eating all the others?
That's the National Park Service's dilemma on this storied barrier island. Proof of its problem can be found on a spongy stretch of salt marsh, where one section is fenced off by barbed wire.
Inside the fence, the island's native smooth cordgrass is growing thickly, a foot tall. Outside it, the grass is cropped nearly to the roots.
"Inside. Outside. A lot different," said Mark Sturm, a Park Service ecologist, gesturing at the denuded muck. The culprit is obvious: There's only one animal on Assateague that can't get through the fence.
"This is all horses," Sturm said.
Yes. Those horses. About 140 wild ponies live on the Maryland half of the island -- less famous than their cousins in Virginia, who star in the annual Chincoteague pony penning, but still a major part of the Assateague mystique.
Now, Park Service officials say, the horse population is eating away at the plants that underpin rare coastal ecosystems here. They're considering a radical solution: selling or relocating as much as a third of the Maryland herd.
"There is no doubt in my mind," Sturm said, "that in the absence of action, things are only going to get worse."
Assateague Island stretches 37 miles along the Atlantic Coast of the Eastern Shore, from Chincoteague, Va., almost to Ocean City, Md. In between, officials say, is the kind of wilderness that has become rare on the East Coast: nearly pristine sand dunes, salt marshes and coastal forests.
But much as scientists treasure the island's rare birds and flora, it is neither the piping plover nor the sea beach amaranth plant that has imbedded Assateague in childhood memories and young-adult fiction.
It's the ponies.
Famous for their celebrated swim
Horses have lived on the island since the 1600s, possibly descended from livestock that farmers stashed here to avoid taxes. They became famous in 1947 with the publication of "Misty of Chincoteague." The book celebrates an annual ritual in which horses on the Virginia side of the island are rounded up and made to swim across a channel to Chincoteague. There, some are auctioned off to benefit the town's volunteer fire department.
Now, there are two herds on the island, separated by a fence at the state line. The Virginia horses are owned by the fire department. The ones in Maryland, which roam across a national seashore and a state park, belong to the Park Service.
The Maryland herd included 28 horses in 1968. But without predators or firefighters to bother them, the ponies multiplied: By 1994, there were 166, and managers were already worried the animals would eat the island bare.
First, birth control was tried. Starting in 1994, biologists with special rifles and a good deal of patience have tracked down female horses and shot them with contraceptive-filled darts. Each female horse is allowed to give birth to only one foal in her lifetime.
The program worked, but not as fast as managers hoped. Without the stress of repeated motherhood, female horses started living years longer than they previously had, which kept the numbers up.
"The population is still more than the island ecosystem can sustain," said Carl Zimmerman, chief of resource management with the national seashore.
'If the dunes go away, the island goes away'
These days, the horses' prodigious appetite -- about 21,000 calories a day for an adult -- has altered all corners of the island. It leaves marsh birds called rails without tall grasses to hide in. It makes meals out of sea-beach amaranth, a federally threatened species.
And it leaves sand dunes without American beach grass, whose tufts and runners hold the sand in place. That's no minor problem, because Assateague is basically one enormous dune.
"If the dunes go away, the island goes away," said Ronald Pilling, past president of the Assateague Coastal Trust, an environmental group.
But no similar problem has been noticed on the Virginia side of the island, which has about the same land area and the same number of horses as Maryland's half. That might be because some sensitive areas, such as beaches and dunes, are fenced off there.
Or it could be, officials say, that the Park Service has done more research on the Maryland side.
Round up?
On the Maryland side, Park Service officials say they want to reduce the horse herd by 40 to 60 animals. They stress that killing the horses is not an option and that they're unlikely to fence them in permanently. But the horses could be sent away: either sold or taken to privately owned sanctuaries on the mainland. The potential solutions were first reported by the Daily Times of Salisbury, Md.
Animal-rights groups have pushed for another option -- to wait for the contraceptive program to reduce the population on its own. That might take six years or more, but they say it's worth it.
"These are wild animals, and there's nothing they're going to want to do less than be rounded up," said John Grandy, senior vice president for wildlife at the Humane Society of the United States. "There's no reason to put those magnificent animals through that."
Park managers say they expect to make a final decision next year.