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Disappearing shorebirds get a close look
Drop in red knots well-known, but many others on decline
By MOLLY MURRAY, The News Journal
Posted Saturday, May 19, 2007
SLAUGHTER BEACH -- In the palm of Nigel Clark's hand rests one of ornithology's great mysteries: the red knot.
Generations of this little rust-breasted bird have migrated from the southern tip of South America to the shores of Delaware Bay to feed on horseshoe crab eggs.
With the red knot population in decline, scientists gather here to capture the birds and pass them between each other, banding, weighing, plucking feathers for DNA and swabbing to test for avian influenza -- adding to an already weighty body of scientific information.
For years, the red knots have drawn such attention from scientists from around the world. But in the meantime, populations of other shorebirds have plummeted and now state officials and a global contingent of researchers are beginning to ask why.
Take the ruddy turnstone. Clark, who has been coming to Delaware Bay each spring since 1998 -- said they used to be plentiful.
The peak numbers, said Kevin Kalasz, an assistant zoologist with the Delaware Natural Heritage Program, were around 50,000 birds. Now, state officials estimate the number passing through Delaware Bay at about 18,000.
"The numbers have declined very dramatically [in Delaware] and on the spot they are stopping over in the fall," Clark said, referring to the Bay of Fundy off the coast of New England, where the number of turnstones have dropped from about 250,000 to around 50,000.
"We don't quite understand what's going on," said Clark, head of projects for the British Trust for Ornithology.
But one thing is certain: Populations of many species, such as the dublin, the semipalmated sandpiper and the sanderling, are on the decline.
An International Shorebird Survey, analyzing data from thousands of bird counts in the U.S., found that 21 species suffered population declines of as much as 25 percent since the 1970s.
But compiling research is difficult in many cases because the birds do not congregate in one area.
Red knots, on the other hand, gather in one place, allowing scientists to learn more about the decline in population.
Scientists believe that overharvesting of horseshoe crabs in the mid-1990s is to blame. They are waiting to see whether a two-year moratorium on commercial harvests of the crabs will help red knots rebound.
But since the crabs are used as bait and are especially effective as an attractant for conch and eel, commercial fishermen have challenged the moratorium in a still-pending lawsuit. Meanwhile, fisheries management agencies and regulators along the Atlantic Coast have dramatically cut the harvest of horseshoe crabs in the past decade.
This year, Kalasz said, the major focus is looking at the bird to see how much weight they gain during the brief Delaware Bay stopover.
Researchers working in New Jersey have been worried that red knots -- which they believe depend on an abundance of horseshoe crab eggs to get enough to eat -- don't gain as much weight as they used to. The birds typically gained 8 grams a day, but in recent years, the number has dropped to 2 grams, New Jersey researchers found.
And there are other concerns.
Laughing gulls also feed on horseshoe crabs eggs and may be competing for a limited resource. Larger gulls are predators of some shorebirds, as are peregrine falcons.
This week, with the birds converging in one area, the research teams work quickly to gather as much data as they can.
They set a cannon net at Slaughter Beach and waited for the birds to shift feeding areas.
At low tide, they congregate at Mispillion Harbor to feed on horseshoe crab eggs. As the tide rises they move south to Slaughter Beach.
As the tide slowly turns, streams of shorebirds begin to fly parallel to the shoreline.
Some begin to land within the net zone.
Clark and Kalasz, who lead this research effort, crouch in the dune grass, waiting and watching.
"Here they come," Kalasz said.
"Three, two, one" -- then comes the pop of the firing mechanism, the drop of the net and the clatter of hundreds of birds.
The team of researchers quickly begins removing the birds and placing them in holding cages.
"That's lovely, folks," Clark said. "Lovely catch."
<!--End Article6.pbo--> Disappearing shorebirds get a close look
Drop in red knots well-known, but many others on decline
By MOLLY MURRAY, The News Journal
Posted Saturday, May 19, 2007
SLAUGHTER BEACH -- In the palm of Nigel Clark's hand rests one of ornithology's great mysteries: the red knot.
Generations of this little rust-breasted bird have migrated from the southern tip of South America to the shores of Delaware Bay to feed on horseshoe crab eggs.
With the red knot population in decline, scientists gather here to capture the birds and pass them between each other, banding, weighing, plucking feathers for DNA and swabbing to test for avian influenza -- adding to an already weighty body of scientific information.
For years, the red knots have drawn such attention from scientists from around the world. But in the meantime, populations of other shorebirds have plummeted and now state officials and a global contingent of researchers are beginning to ask why.
Take the ruddy turnstone. Clark, who has been coming to Delaware Bay each spring since 1998 -- said they used to be plentiful.
The peak numbers, said Kevin Kalasz, an assistant zoologist with the Delaware Natural Heritage Program, were around 50,000 birds. Now, state officials estimate the number passing through Delaware Bay at about 18,000.
"The numbers have declined very dramatically [in Delaware] and on the spot they are stopping over in the fall," Clark said, referring to the Bay of Fundy off the coast of New England, where the number of turnstones have dropped from about 250,000 to around 50,000.
"We don't quite understand what's going on," said Clark, head of projects for the British Trust for Ornithology.
But one thing is certain: Populations of many species, such as the dublin, the semipalmated sandpiper and the sanderling, are on the decline.
An International Shorebird Survey, analyzing data from thousands of bird counts in the U.S., found that 21 species suffered population declines of as much as 25 percent since the 1970s.
But compiling research is difficult in many cases because the birds do not congregate in one area.
Red knots, on the other hand, gather in one place, allowing scientists to learn more about the decline in population.
Scientists believe that overharvesting of horseshoe crabs in the mid-1990s is to blame. They are waiting to see whether a two-year moratorium on commercial harvests of the crabs will help red knots rebound.
But since the crabs are used as bait and are especially effective as an attractant for conch and eel, commercial fishermen have challenged the moratorium in a still-pending lawsuit. Meanwhile, fisheries management agencies and regulators along the Atlantic Coast have dramatically cut the harvest of horseshoe crabs in the past decade.
This year, Kalasz said, the major focus is looking at the bird to see how much weight they gain during the brief Delaware Bay stopover.
Researchers working in New Jersey have been worried that red knots -- which they believe depend on an abundance of horseshoe crab eggs to get enough to eat -- don't gain as much weight as they used to. The birds typically gained 8 grams a day, but in recent years, the number has dropped to 2 grams, New Jersey researchers found.
And there are other concerns.
Laughing gulls also feed on horseshoe crabs eggs and may be competing for a limited resource. Larger gulls are predators of some shorebirds, as are peregrine falcons.
This week, with the birds converging in one area, the research teams work quickly to gather as much data as they can.
They set a cannon net at Slaughter Beach and waited for the birds to shift feeding areas.
At low tide, they congregate at Mispillion Harbor to feed on horseshoe crab eggs. As the tide rises they move south to Slaughter Beach.
As the tide slowly turns, streams of shorebirds begin to fly parallel to the shoreline.
Some begin to land within the net zone.
Clark and Kalasz, who lead this research effort, crouch in the dune grass, waiting and watching.
"Here they come," Kalasz said.
"Three, two, one" -- then comes the pop of the firing mechanism, the drop of the net and the clatter of hundreds of birds.
The team of researchers quickly begins removing the birds and placing them in holding cages.
"That's lovely, folks," Clark said. "Lovely catch."
<!--End Article6.pbo--> Disappearing shorebirds get a close look
