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As species recover, some threaten others in more dire shape

Lake Michigan

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Hidden behind trees near Lake Michigan, two scientists remotely manipulated a robotic owl on the forest floor. As the intruder flapped its wings and honked its horn, a Merlin guarding its nest in a nearby pine tree shot overhead, high-pitched, quick distress calls.

The little falcon dove toward the enemy—and into a net that Smithsonian interns Tim Baerwald and Zachary Bordner had strung between steel posts. They carefully detached the brown-speckled marlin, then attached a leg strap and a backpack transmission unit so researchers could track the mother bird’s movements.

“As long as it fits right, she’ll have a long and happy life,” Baerwald said before Bordner released the marlin, which rustled back to his nest tree.

The mission will increase knowledge of a species still recovering from a significant decline caused by pesticides, including DDT, which was banned in 1972 after harming many birds of prey. It also helps the managers of Sleeping Bear Dunes National Lakeshore to protect the black-throated plover, an endangered shorebird that is killed and eaten by merlins.

“Merlins pose a major threat to their recovery,” said Nathan Cooper, a research ecologist at the Smithsonian’s National Zoo and Conservation Biology Institute.

The situation is ironic: A troubled species recovers thanks to recovery efforts, only to make matters worse for others who are in danger by hunting or beating them for food and living space. Similar conditions have occurred elsewhere, challenging wildlife experts who want all of them to thrive in a balanced, healthy environment.

For example, the comeback of the iconic bald eagle has put rare waterfowl under pressure. Resurgent peregrine falcons threaten endangered California terns and western snow plovers that take refuge at naval bases near San Diego. And off the coast of California, protected white shark attacks are hampering the recovery of endangered sea otters.

Gray seals previously on the brink of extinction in New England waters now occupy hundreds of beaches in Massachusetts. The return of the 800-pound mammal has raised concerns about vulnerable fish stocks.

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

“Obviously there are situations where we get these conflicts between species that we’re trying to protect,” said Stuart Pimm, an extinction specialist at Duke University. “But is it a major concern in conservation? No.”

Species recovery can involve trade-offs, as some animals can adapt better than others to changes in climate or landscape, said Bruce Stein, chief scientist at the National Wildlife Federation.

“A lot of ecosystems where these things take place are kind of off the grid at first, because we’ve changed them in some way,” Stein said. “With climate change, there will be winners and losers. The losers tend to have specific habitat requirements, narrow ecological niches, and will often be the ones that are already declining.”

The Great Lakes region is home to an estimated 65 to 70 pairs of sand-backed, ring-necked plovers that skim beaches and nibble on small sea creatures and eggs. They are among the three remaining North American populations, their decline is mainly caused by habitat loss and predation.

Meanwhile, numbers of merlins in the region have risen. Over the past 10 to 15 years, they are suspected of killing at least 57 adult plovers, Cooper said.

While officials have shot a number of merlins, they are looking for non-lethal checks. Data from the transmitter backpacks can help determine whether it’s worth catching and moving them, said Vince Cavalieri, a biologist at the Lake National Lake.


The recovery of America’s national bird, the bald eagle, is a triumph. But in one of the coastal areas of Maine, the large bird of prey poses a problem for the only American breeding population of great cormorants.

“If disturbed by eagles, the adult cormorants will flush and leave their nest,” said Don Lyons, a naturalist with the National Audubon Society’s Seabird Institute.

Then gulls, ravens and crows dive in to eat 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, the fewest terns and snow plovers are no match for attacking peregrine falcons, who bounced back like eagles after the DDT ban. Such pesticides are passed down the food chains and cause large birds to produce eggs with thin shells, which crush females when trying to breed them.

The San Diego Zoo and Wildlife Alliance is trying to protect the endangered birds by hiring a falconer to capture peregrine falcons, keep them in a sanctuary for the winter, or release them in Northern California. Some are finding new territory, while others are moving back, said Nacho Vilchis, a conservation ecologist.

“If there is a real problem bird that keeps returning, we can request permission for lethal removal, but that rarely happens,” Vilchis said.

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

Fishing groups claim the seals could pose a threat to the cod stocks that regulators are struggling to recover after decades of overfishing.

The Coastal Ecosystem Alliance, based in Fairhaven, Massachusetts, wants to water down the conservation law to allow hunting and slow the growth of the seal population, board member Peter Krogh said.

“Gray seals are definitely this case where recovery is both cause for celebration and concern,” said Kristina Cammen, a marine mammal scientist at the University of Maine who says they are less dangerous to fish populations than humans.


Like the seal and cod confrontation, there are other instances where the revival of species can be more of a nuisance to humans than a threat to other wildlife.

Fish farmers in the south and fishermen in the Great Lakes and Pacific Northwest have long complained about the double-crested cormorant, a dark-feathered diving bird that feeds on catfish, bass, salmon and other prized species.

Cormorants have done so well since the DDT ban that agencies have tried to limit them in some locations through egg oil, nest destruction and even shooting — filing lawsuits from environmentalists who say the birds are a scapegoat for human actions that harm fish.

“They’re part of our bird community and our ecosystems, and there has to be a place for them,” said Dave Fielder, a fisheries research biologist with the Michigan Department of Natural Resources. “But when their numbers are so high that they potentially decimate recreational fisheries, that’s a problem.”

Wild turkeys had spread throughout North America before European settlement, but had dwindled to tens of thousands by the 1930s and disappeared from many states. Now they are hunted in 49 states and are so common in New England that they often cause traffic jams.

Some hunters say that hungry turkeys outnumber the ruffled grouse, which are declining in parts of their range, such as the Upper Midwest. But scientists point to habitat loss and climate change.

The National Wild Turkey Federation is helping move turkeys from states with plenty — such as North Carolina, Maine and West Virginia — to Texas and others that could use more, said Mark Hatfield, national director of conservation services.

“If you introduce the hunt for localized wild turkeys, you immediately reduce the problem with bountiful turkeys,” Hatfield said.


Conflicts between recovering species and species still in trouble don’t always mean something is wrong, scientists say. It could reflect a return to how things were before people got in the way.

“When a population returns to where it has the same interactions with other organisms as before it went down, that’s nature at work,” said John Fitzpatrick, director emeritus of Cornell University’s Laboratory of Ornithology.

The bald eagle “challenges our preconceptions about what’s normal” for prey such as cormorants in New England and common guillemots on the west coast, which may have been less abundant before the eagles waned, said Lyons of the Audubon Society.

The eagle’s recovery “complicates the conservation of certain other species,” Lyons said. “But their recovery is such a wonderful result… that’s a welcome complication.”

Predator-prey relationships are complex and intervening can be tricky, said Stein of the Wildlife Federation. It’s often wiser, he said, to focus on protecting habitats and reconnecting fragmented landscapes to promote natural migration than “moving things randomly.”

But environmental scientist Ian Warkentin, a merlin specialist, said there may be ways to help struggling species without being heavy-handed. Larger falcons, such as peregrine falcons that are sometimes used to repel birds from airports, can be used to chase merlins from plover breeding grounds.

“I’m falling on the side of the fence that says we must do everything we can … to aid the recovery of species for which we have caused so much grief,” said Warkentin of Memorial University of Newfoundland’s Grenfell Campus.

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Quote: As species recover, some others threaten others in a more dire state (2022, August 1), retrieved August 1, 2022 from https://phys.org/news/2022-08-species-recover-threaten-dire.html

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