Research on rare shorebirds in New Jersey is giving scientists a greater appreciation for their Herculean flights.
The red knot makes one of the longest annual migrations of any animal on the planet — 16,600 miles round trip, from the tip of South America through Cape May County to the extreme arctic and back.
For the past two years, scientists with the Conserve Wildlife Foundation of New Jersey have been catching and banding red knots with a little tag that uses the rising and setting sun to pinpoint the bird’s location day by day as it treks across the globe.
One of the recovered bands showed that a red knot flew nonstop over six days and six nights between southern Brazil and North Carolina — a distance of 5,000 miles. That is the equivalent of flying nonstop — without food, water or rest — from Atlantic City to Los Angeles and back.
“It’s amazing for any bird,” lead scientist Larry Niles said.
This rivals the single-longest bird flight known to science - the bar-tailed godwit’s annual 7,100-mile odyssey between Alaska and New Zealand.
A study reporting the results was published in the journal International Wader Study Group.
Unlike hawks or songbirds that travel between daily stops for feeding and sleeping, red knots and other shorebirds have far fewer places to stop, especially as they traverse human development or thick rainforest, Niles said.
These birds seem to have evolved to migrate in a single bound, perhaps to avoid predators or disease.
“Birds will often rest and restore themselves each day,” he said. “So what’s surprising about red knots and other shorebirds is they’re making these long flights over six or eight days at a time.”
But red knots and other shorebirds are remarkable eaters, too.
Scientists think New Jersey’s Delaware Bay is crucial to the birds’ evolutionary migration. They stop at beaches in Middle and Lower townships to gorge on the eggs of horseshoe crabs that spawn each spring. This helps the birds literally fatten up for the arduous trip to their arctic breeding grounds.
The dove-sized birds arrive on the Delaware Bay emaciated at a scant 90 grams. Two weeks later, when they leave New Jersey for the arctic, they have more than doubled their weight, gaining 6 to 8 grams per day.
When they depart, they carry the porcine proportions of flying footballs.
Niles said this northbound migration is more urgent for the birds. The later the birds arrive on the tundra, the less chance their chicks will fledge safely before cold weather arrives.
Their digestive organs shrink while their flight muscles get bigger, Niles said.
“It is kind of a superpower,” Niles said. “When they get toward their flight weight, which we estimate at 180 grams, they start to transform their organs.”
The birds’ southbound route also takes them through New Jersey but at a more leisurely pace and in smaller groups. Some of the southbound birds were observed on beaches in Stone Harbor and Brigantine last week, where they were molting or replacing their flight feathers.
But how do these little birds stay awake for six to nine days?
Mike Crewe, a naturalist for New Jersey Audubon’s Cape May Bird Observatory, said while shorebirds do not sleep, per se, they do shut down hemispheres of their brains during these long-distance flights. This is how cetaceans such as dolphins slumber, too.
“I think it is one of those things we struggle to come to terms with,” he said. “It’s something we are physically incapable of. It’s tough to imagine it from the human condition.”
Likewise, the bird’s ability to double its body weight in a matter of weeks is far beyond human experience.
“Doubling our body weight would kill us. Every species is as adapted as it needs to be — to be that species,” he said.
Niles has been studying red knots for more than a decade. He said the increasing frequency and severity of coastal storms expected from global climate change could create daunting hurdles for red knots and other shorebirds. Red knots migrate south at the peak of the Atlantic hurricane season.
One of the studied birds detoured hundreds of miles around a hurricane before aborting the trip and returning to land.
“We’ve seen an increasing frequency of tropical storms and hurricanes, which comes right when these birds are heading south,” Niles said. “It creates greater dangers that they haven’t encountered in the past.”
Niles will affix geo-locating bands to more shorebirds this month in the Gulf of Mexico. And he plans to recapture the banded birds when they return to New Jersey in the spring.
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