Twice a year, the rufa red knot performs one of the planet’s most amazing migrations. After wintering in the southern reaches of Argentina and Chile, the red knot will fly roughly 9,300 miles (15,000 kilometers) north, eventually reaching the Canadian Arctic for a summer of mating and breeding. Come fall, it will return south, this robin-size bird with a mere 20-inch (51-centimeter) wingspan flying without rest for stretches of up to 1,500 miles (2,400 kilometers).
For this incredible voyage, Calidris canutus needs fuel, and a lot of it. As it happens, one of its main food supplies, the eggs of horseshoe crabs in the Delaware Bay, where the birds recharge for the final leg of their journey, has become scarce, and red knot populations are suffering.
The population declines are bad enough that last Friday, the U.S. Fish and Wildlife Service (FWS) officially proposed “threatened” status for the rufa red knot under the Endangered Species Act (ESA).
In a press conference, FWS director Dan Ashe explained that in some areas surveyed, red knot populations “have declined by about 75 percent since the 1980s, with the steepest declines happening after 2000.”
Experts from the Fish and Wildlife Service and from the American Bird Conservancy (ABC), a nonprofit advocacy group that has petitioned for the bird’s protection under the ESA for eight years now, all point to the scarcity of horseshoe crabs in the Delaware Bay region as a primary factor in the red knot’s decline. As Fish and Wildlife spokesperson Meagan Racey explained, “Delaware Bay is the only area in which knots feed on horseshoe crab eggs, and it hosts the largest concentration of knots in the world during the spring stopover that lines up with horseshoe crab spawning. “
Eggs and Knots
How crucial a fuel are these eggs to the red knot? According to Steve Holmer, senior policy analyst for ABC, the horseshoe crab binge lasts a few days, during which the birds “accumulate body fat for the long continuing journey to their Arctic breeding grounds.”
Holmer points to the FWS listing proposal itself, which describes actual “physiological changes” that take place in the birds while they feast on the eggs. “Before takeoff, the birds accumulate and store large amounts of fat to fuel migration and undergo substantial changes in metabolic rates,” the proposal states. “In addition, leg muscles, gizzard (a muscular organ used for grinding food), stomach, intestines, and liver all decrease in size, while pectoral (chest) muscles and heart increase in size.”
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