As species recover, some threaten others in more serious condition
In a forest near Lake Michigan, two scientists attached a backpack-tracking device to a swivel they had caught in a net. The mission: to help prevent predatory species from gobbling up piping plovers, highly endangered shorebirds that nest nearby.
Merlins themselves were in decline decades ago but are recovering thanks to the banning of pesticides such as DDT. It’s good for them, but not for the plovers in the Great Lakes region, where there are only 65 to 70 pairs left. Small hawks “pose a big threat to their recovery,” said Nathan Cooper, an ecologist researcher at the Smithsonian’s National Zoo and Conservation Biology Institute.
The situation is ironic. A struggling species bounces back through restoration efforts, only to make matters worse for others in peril by preying on them or overtaking them for food and living space. Similar circumstances have occurred elsewhere, challenging wildlife experts who want them all to thrive in balanced and healthy environments.
For example, the return of the iconic bald eagle has put pressure on rare waterfowl. The resurgence of peregrine falcons threatens less threatened California terns and western snowy plovers that take refuge in naval bases near San Diego. And, off the California coast, attacks by protected white sharks are hampering the recovery of endangered sea otters.
Gray seals, once on the verge of extinction in New England waters, now occupy some Massachusetts beaches in their hundreds. The return of the 800-pound mammal has raised concerns about vulnerable fish stocks.
Experts say such unintended consequences do not necessarily reveal flaws in US endangered species law or conservation programs. Rather, they illustrate the complexity of nature and the importance of protecting biological communities, not just individual species.
“Obviously there are occasions where we have these conflicts between the species that we’re trying to protect,” said Stuart Pimm, an extinction specialist at Duke University. “But is this a major conservation concern? Nope.”
Species recovery can produce trade-offs because some animals are more adaptable 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 happen are a little out of whack to begin with because we’ve altered them in some way,” Stein said. “With climate change, there will be winners and losers. The losers will tend to have specific habitat needs, narrow ecological niches, and will often be those that are already in decline.
Outsmart a merlin
Smithsonian interns Tim Baerwald and Zachary Bordner caught the merlin at Sleeping Bear Dunes National Lakeshore with the help of its natural enemy: a great horned owl. This one was dead but fitted with remote control devices to make it honk and flap its wings.
The merlin streaked overhead, emitting quick, high-pitched distress calls. He dove into a net stretched between steel posts. Scientists carefully disentangled the brown-spotted female, then attached the tracker and a leg band.
“As long as it is properly adjusted, she will have a long and happy life,” Baerwald said before Bordner released the merlin, which returned to its nesting tree.
Merlin numbers in the area have jumped since the DDT ban in 1972. They are believed to have killed at least 57 adult piping plovers in the past 10 to 15 years, Cooper of the Smithsonian said.
Sand-backed and ring-necked plovers glide along beaches munching on tiny marine animals and their eggs. They are one of only three remaining North American populations, with their decline primarily caused by habitat loss and predation.
While officials have fired at merlins, they are looking for non-lethal checks. Data from transmitter backpacks could help determine whether it’s worth trying to capture and relocate them, said National Lakeshore biologist Vince Cavalieri.
Eagles threaten rare birds
The recovery of America’s national bird, the bald eagle, is a triumph. But in a coastal area of Maine, the great raptor poses a problem for America’s only breeding population of great cormorants.
“When disturbed by eagles, adult cormorants fly away and leave their nests,” said Don Lyons, conservation scientist at the National Audubon Society’s Seabird Institute.
Then gulls, ravens and ravens swoop in to gobble up the cormorant eggs and chicks. “If this happens repeatedly, an entire colony can fail,” Lyons said.
His team organizes volunteers to camp near gatherings of cormorants to scare away the eagles.
In southern California, pygmy terns and snowy plovers are no match for peregrine falcons, which, like eagles, rebounded from the DDT ban. These pesticides move up food chains and cause large birds to produce thin-shelled eggs, which females crush when they attempt to incubate them.
The San Diego Zoo and Wildlife Alliance tries to protect endangered birds by hiring a falconer to capture problematic basking sharks, keeping them in a holding facility over the winter, or releasing them in northern California. Some find new territory, while others return to it, said Nacho Vilchis, a conservation ecologist.
“If there’s a real bird problem that keeps coming back, we can ask for permission to remove it lethal, but that’s rarely done,” Vilchis said.
Hunting and bounties have devastated the gray seals of New England. Saved by the Marine Mammal Protection Act of 1972, the population has rebounded to the tens of thousands.
Fishing groups argue the seals could threaten cod stocks that regulators are struggling to rebuild after decades of overfishing.
The Coastal Ecosystem Alliance, based in Fairhaven, Mass., wants to weaken the protection law to allow hunting and slow the growth of the seal population, said board member Peter Krogh.
“Grey seals are definitely that case where the recovery has been both a cause for celebration and a cause for concern,” said Kristina Cammen, a marine mammal scientist at the University of Maine, who says they pose less of a risk to fish populations than humans.
Seals, fishing stalking cormorants
Like the conflict over seals and cod, there are other instances where the revival of species may be more of a nuisance to people than a threat to other wildlife.
Southern fish farmers and fishermen in the Great Lakes and Pacific Northwest region have long complained of the double-crested cormorant, a dark-feathered diving bird that gorges on catfish, perch, salmon, and fish. other prized species.
Cormorants have done so well since the DDT ban that agencies have tried to limit them to certain places with egg greasing, nest destruction and even shooting – drawing lawsuits from conservationists who say birds are a scapegoat for human actions that harm fish.
“They are part of our avian community and our ecosystems, and there needs 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 fishing, that’s a problem.”
Wild turkeys were widespread throughout North America before European settlement, but had dwindled to tens of thousands by the 1930s, disappearing from many states. Now they’re hunted in 49 states and are so common in New England that they often cause traffic jams.
Some hunters say hungry turkeys are competing with ruffed grouse, which are dwindling in parts of their range, like the upper Midwest. But scientists point to habitat loss and climate change.
The National Wild Turkey Federation helps move turkeys from wealthy states — like North Carolina, Maine and West Virginia — to Texas and others that could use more of them, said Mark Hatfield, national services manager. conservation.
“If you introduce localized wild turkey hunting, you immediately reduce the problem of overabundant turkeys,” Hatfield said.
nature at work
Conflicts between recovering species and those still struggling don’t always mean that something is wrong, scientists say. It could reflect a return to how things were before humans got in the way.
“When a population returns to where it has the same interactions with other organisms as before it disappeared, that’s nature at work,” said John Fitzpatrick, director emeritus of the University’s Laboratory of Ornithology. Cornell.
The bald eagle “challenges our preconceptions about what is normal” for prey such as great cormorants in New England and common murres on the West Coast, which may have been less abundant before the eagles declined, has said Lyons of the Audubon Society.
The eagle’s recovery “complicates the conservation of some other species,” Lyons said. “But their recovery is such a wonderful outcome…it’s a welcome complication.”
Predator-prey relationships are complex and intervention can be tricky, said the wildlife federation’s Stein. It’s often wiser, he said, to focus on protecting habitat and reconnecting fragmented landscapes to support natural migration rather than “moving things willy-nilly”.
But environmental scientist Ian Warkentin, a merlin specialist, said there could be ways to help struggling species without being too harsh. Larger falcons – such as the peregrines sometimes used to hunt birds from airports – could be deployed to chase merlins from plovers’ nesting areas.
“I fall on the side of the fence that says we should do all we can…to help in the recovery of the species for which we have caused so much grief,” said Warkentin, of Memorial University’s Grenfell campus. of Newfoundland.
Larson reported from Washington, DC, and Whittle reported from Portland, Maine.