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."
Without enough eggs, red knots may not make it to the Arctic at all, or if they do, they arrive in too weak a state to reproduce.
Data analyzed by FWS suggest that an increase in commercial harvests of horseshoe crabs in the early 2000s were a direct and critical factor in the population declines. Although FWS was first asked to consider protection of the bird in 2005, it wasn't until the dire findings of a 2011 population count that the service took action. That 2011 count of wintering populations in South America found a staggering decline of at least 5,000 birds, or roughly one-third of the population, from the previous year.
The Fish and Wildlife Service proposal also highlights other threats beyond this loss of stopover fuel. Climate change is having ill effects on other elements of the red knot's diet and changing the character of its Arctic breeding grounds. The shorebird is also losing areas along its migratory range due to sea-level rise and coastal development.
So if the proposed "threatened" status for the red knot is confirmed, how can the Endangered Species Act offer protection to such an international species? Racey explained, "While the ESA's prohibitions regarding listed species—no harm, no kill, et cetera—apply only to people subject to the jurisdiction of the United States, the ESA can generate conservation benefits beyond its jurisdiction, such as increased awareness of listed species, research efforts to address conservation needs, or funding for in-situ conservation of the species in its range countries."
Holmer added that the ESA "can require states to adopt adequate regulatory mechanisms to limit horseshoe crab harvest," which "thus far, states have not been willing to do."
The service could also designate critical habitat for the shorebird, which, according to a FWS document, "could include sand dunes for roosting or habitat supporting prey, among other elements."
Last week's proposal to list the rufa red knot follows an "exhaustive scientific review" of the species and its habitat, but isn't the last step in the ESA process. By law, the proposal is now open to public comment for 60 days. After that period, the agency will release a final listing determination within a year.