Cape Cod National Seashore plans a pilot program (at Duck Harbor and Bound Brook in Wellfleet) to insert poisoned chicken eggs into fake piping plover nests in a targeted effort to control certain crows that are eating plover eggs.
Cape Cod National Seashore plans a pilot program (at Duck Harbor and Bound Brook in Wellfleet) to insert poisoned chicken eggs into fake piping plover nests in a targeted effort to control certain crows that are eating plover eggs. Crows have learned the exclosures (3-foot-high fences with netting on top) protect defenseless piping plover chicks that can be eaten once they emerge.
The pilot program is set to begin in March and continue until May.
Piping plovers are an endangered species, as per the Endangered Species Act, and efforts to revive the population have been fruitful. In Massachusetts, the number of plover pairs was down to 126 in 1987, one year after the species was federally listed. By 2002, after 15 years of effort, the number was up to 538 and in 2008 it stood at 566. A similar rebound has occurred all along the Atlantic Coast where pair numbers are up from 790 in 1986 to 1,848 in 2008. The Seashore is home to 15 percent of the state population, and its pair count has bounced from 15 in 1985 to 87 last summer.
Unfortunately, crow numbers are also up, due to human activity. This is one reason plover productivity has dropped from 2.03 chicks per Massachusetts nest in 1992 to 1.19 on the Atlantic Coast and 1.41 in Massachusetts in 2008. Last summer the chicks per nest fell below the replacement rate of 1.25, mainly due to all the storms.
But crows played their part as well.
“We have a very extensive monitoring program and have put in thousands of hours observing (plovers) and 35 percent of the eggs lost are due to crow predation,” explained Megan Tyrell, acting director of natural resources at Cape Cod National Seashore.
Many other eggs were washed away by last spring’s storms.
“Crows are keying into the habitat and they’ve learned the upper beach habitat means food so they patrol there in search of eggs,” said Mary Hake, the Seashore’s shorebird biologist. “The plovers lay eggs on the open beach, a clutch of four eggs. The crows are taking the first egg they lay and when that happens, the plovers will relay a second clutch in seven to 10 days. So that extends the season.”
That can also extend beach closures into late July or August if it happens often enough.
Biologists don’t put predator exclosures over a nest until two or three eggs are laid and the plover begins incubating them. Some birds are spooked by the exclosure and abandon the nest. Predators, such as crows, also learn to associate the exclosures with food.
“Another drawback to exclosures is over the last 15 years we’re seeing more adult mortality because of them,” Hake said. “Predators are keying into exclosures and kill the adult birds when they come out. So we don’t want to put them up haphazardly. We have found 15 (dead) adults near exclosures.
“They’re smart predators. They’ve learned a behavior. I have observed crows walking around outside an exclosure and that would cause abandonment of the eggs,” Hake said. “They wait for the chicks to come outside the safety of the exclosure and eat them.”
Plover chicks are up and about in less than 12 hours after hatching. They can feed themselves but can’t fend off a foe.
The Animal and Plant Health Inspection Service, a division of the USDA, will handle the poisoning.
“They are going to put a hard-boiled chicken egg in the enclosure (without netting on top) inside a simulated piping plover nest,” Tyrell said. “There will also be symbolic fencing. They’ll wait for the crows to take a plain egg and subsequently put in an egg with poison to specifically target predators that have learned to associate the enclosure with food.”
Crows are a natural predator but they’re made more natural by people. They adapted to a human-altered environment and their numbers are up.
“We’re focusing on crows because the population benefits from human activity in the coastal zone,” Tyrell said. “Plovers are a threatened species. If crows were eating gray squirrels, it wouldn’t be an issue.”
The poison to be used is DRC-1339, a slow-acting avicide, also known as Starlicide, geared to blackbirds. The poison should kill the crows in one to three days. It is most often used in Midwestern agriculture on starlings, blackbirds, grackles and cowbirds.
Two grams will be used over 100 eggs and that amount won’t kill a gull that might eat an egg. Uneaten eggs will be collected each evening.
Since the eggs will be inside a 3-foot fence, it’s unlikely other predators will eat them. The poison breaks down quickly.
“If a hawk eats (a dead crow), it would not be affected by it,” Hake said. “It does not have a secondary effect on other wildlife.”
A similar program has been used at Crane’s Beach in Ipswich and when the “smart crows” were eliminated, there was a gap of time before other crows learned to hunt the eggs.
“It’s a very limited number of crows that are doing the damage, a handful,” Hake said.
The Cape Codder