As species recover, some threaten others in more dire shape

GLEN ARBOR, Mich. — In a forest near Lake Michigan, two scientists attached a backpack tracking device to a merlin they’d lured into a net. The mission: help prevent the predatory species from gobbling up piping plovers — highly endangered shorebirds that nest nearby.

Merlins themselves were going downhill decades ago but are recovering, thanks to bans on pesticides such as DDT. That’s good for them — but not for plovers in the Great Lakes region, where only 65 to 70 pairs remain. The small falcons are “are a big threat to their recovery,” said Nathan Cooper, a research ecologist with Smithsonian’s National Zoo and Conservation Biology Institute.

The situation is ironic. A troubled species rebounds thanks to restoration efforts, only to make things worse for others in peril by preying on them or outcompeting them for food and living space. Similar circumstances have turned up elsewhere, challenging wildlife experts who want them all to thrive in balanced, healthy environments.

For instance, the iconic bald eagle’s comeback has pressured rare water birds. Resurgent peregrine falcons menace endangered California least terns and Western snowy plovers that take refuge at naval bases near San Diego. And, off the California coast, attacks from protected white sharks hinder the recovery of threatened sea otters.

Gray seals previously on the brink of extirpation in waters of New England now occupy some Massachusetts beaches by the hundreds. The 800-pound mammal’s return has raised worries about vulnerable fish stocks.

Such unintended consequences don’t necessarily reveal flaws in the U.S. Endangered Species Act or conservation programs, experts say. Rather, they illustrate nature’s complexity and the importance of protecting biological communities, not just individual species.

“Clearly there are occasions when we get these conflicts between species that we’re trying to protect,” said Stuart Pimm, a Duke University extinction specialist. “But is it a major worry in conservation? No.”

Species recoveries can produce tradeoffs since some animals are more adaptable than others to changes in the climate or landscape, said Bruce Stein, chief scientist with the National Wildlife Federation.

“A lot of ecosystems where these things are occurring are a little out of whack to begin with because we’ve altered them in some way,” Stein said. “With climate change, there are going to be winners and losers. The losers will tend to have specific habitat requirements, narrow ecological niches, and often will be the ones already declining.”

Outsmarting a merlin

Smithsonian interns Tim Baerwald and Zachary Bordner snared the merlin at Sleeping Bear Dunes National Lakeshore with help from its natural enemy: a great horned owl. This one was dead but fitted with remote-control devices to make it hoot and flap its wings.

The merlin darted overhead, sounding high-pitched, rapid-fire distress calls. It dove into a net stretched between steel poles. The scientists gently disentangled the brownish-speckled female, then attached the tracker and a leg band.

“As long as it’s fitted correctly, she’ll have a long and happy life,” Baerwald said before Bordner released the merlin, which zipped back to its nesting tree.

Merlin numbers in the region have jumped since the DDT ban in 1972. They’re suspected of killing at least 57 adult piping plovers in the past 10 to 15 years, said Cooper of Smithsonian.

The sandy-backed, ring-necked plovers skitter along beaches nibbling tiny marine animals and eggs. They’re among three remaining North American populations, their decline caused primarily by habitat loss and predation.

While officials have shot some merlins, they’re looking for non-lethal controls. Data from the transmitter backpacks might help determine whether capturing and relocating them is worth trying, said Vince Cavalieri, a biologist with the national lakeshore.

Eagles threaten rare birds

Recovery of America’s national bird, the bald eagle, is a triumph. But in one area of coastal Maine, the big raptor poses a problem for the only U.S. breeding population of great cormorants.

“When they’re disturbed by eagles, the adult cormorants will flush and leave their nests,” said Don Lyons, a conservation scientist at the National Audubon Society’s Seabird Institute.

Then gulls, ravens and crows swoop in to gobble cormorant eggs and chicks. “If this happens repeatedly, an entire colony can fail,” Lyons said.

His team organizes volunteers to camp near cormorant gatherings to scare away eagles.

In Southern California, least terns and snowy plovers are no match for attacking peregrine falcons, which like eagles bounced back after the ban on DDT. Such pesticides are passed up food chains and cause large birds to produce eggs with thin shells, which females crush when trying to incubate them.

The San Diego Zoo and Wildlife Alliance tries to protect the endangered birds by hiring a falconer to capture problem peregrines, keeping them in a holding facility over winter or releasing them in Northern California. Some find a new territory, while others go back, said Nacho Vilchis, a conservation ecologist.

“If there’s a real problem bird that keeps returning, we may ask for permission for lethal removal, but that’s only rarely done,” Vilchis said.

Hunting and bounties devastated New England’s gray seals. Saved by the Marine Mammal Protection Act of 1972, the population has rebounded to tens of thousands.

Fishing groups contend the seals could threaten cod stocks that regulators are struggling to rebuild after decades of overfishing.

The Coastal Ecosystem Alliance, based in Fairhaven, Massachusetts, wants to weaken the protection act to allow hunting and slow the seals’ population growth, said board member Peter Krogh.

“Gray seals are certainly this case where recovery has both been cause for celebration and cause for concern,” said Kristina Cammen, a University of Maine marine mammal scientist who says they’re less of a hazard to fish populations than humans are.