Monday, June 02, 2008

Red Knot Migration Delayed

A few weeks ago a major storm swept up the Atlantic coast and disrupted the normal cycle of horseshoe crab spawning. The lack of crabs and crab eggs left returning red knots – and other shorebirds – with little to eat before they resume their northward migration. The situation has stabilized somewhat, but the red knot's status is even more precarious than before.

After early 2008 winter counts in South America showed red knots at an all-time low, biologists say there's not much margin left to keep the western Atlantic red knot subspecies from slipping closer to extinction, if they don't get enough food this week before the final leg of their annual flight north to breeding grounds in Canada's Arctic.

"For the first time in 12 years, when I sent an update back to Australia, I've used the words "The birds are starving,' " said Clive Minton, who works on an international group that has helped New Jersey state biologists monitor red knots since the mid-1990s.

"But in the last five days, the weather has calmed down and warmed up, so they're putting on weight," Minton said as the team mounted up Friday to catch and release red knots and check their weight gain. "It depends on the next three or four days."
Red knots are fattening themselves, but their weight gain is happening later than usual.
"I'd rather see them over 180 grams by now," Niles fretted, as birds weighed in between 150 and 179 grams. Weight gain is a key indicator of the red knots' future chance of success with migrating and raising young in Canada's far north. If they don't eat enough here to build up fat reserves, the red knots will fall short, like jet fighters flaming out.

"If they get to 180 (grams body weight) the energy in that fat is enough to get them to the Arctic," Niles said. "Back in the old days, we regularly had birds going over 200 grams. Now, it's a rare event."

Once he made the rounds of wildlife pros and volunteers measuring the birds, Niles felt better. "There's a mix," he reported. "Some birds are making above 180 grams."

"We've got a fatty!" announced Anneke Walsh, 11, whose family came from Bryn Mawr, Pa., to help with the sampling. A bird had just tipped the electronic scale at nearly 200 grams.
The fact that red knots are reaching their normal migration weight is a good sign. However, if the process is taking longer than usual, it could still interfere with their breeding. Red knots have a relatively small window in which to find a mate, lay and incubate eggs, and raise chicks in the short Arctic summer. Delayed migration could narrow that breeding window even further.