Shorebirds are the undisputed marathon champions among migratory birds. About 20 species of shorebirds have been recorded making nonstop flights longer than 5,000 kilometers, or 3,100 miles—about the distance from Boston to San Francisco. No other species of migratory bird has been recorded completing a nonstop flight longer than 4,000 km.
The longest known shorebird flights—about 12,000 kilometers and nine days in length—belong to the Bar-tailed Godwit during its migration from Alaska to New Zealand. But even small shorebird species make epic flights. The Semipalmated Sandpiper, which at about 22 grams weighs less than an apple, makes nonstop flights of 5,300 kilometers from Canada to South America—that’s the aerial equivalent of completing 126 consecutive marathons.
To accomplish these incredible migratory feats, shorebirds are legendary gorgers. Red Knots stopped over in the Delaware Bay on migration feast on horseshoe crab eggs and more than double their body mass in just three weeks. Not all of that food goes toward fuel. Research on Whimbrels stopped over in Chesapeake Bay showed that the protein from a feast of crab eggs went directly into producing eggs when the Whimbrels arrived on their breeding grounds in Churchill, Manitoba, just days later.
In this way, shorebirds rely on habitat across hemispheres, which means shorebird conservation requires international efforts. Protecting important habitat for a single shorebird species could unite a native Inuit community in Alaska, a California rice farmer in the Central Valley, and a Mexican fishing village in a shared goal. Shorebirds are a unique opportunity for conservation diplomacy—a chance to bring the peoples of the Americas together for birds.
How Do They Manage Such Extreme Endurance?
Flight is one of the most energetically costly forms of locomotion, with long-distance flight being especially expensive and requiring a suite of incredible physiological adjustments. Scientists are still just beginning to understand the incredible athletic feats of shorebirds, only recently discovering that some shorebirds migrate at the altitudes of jet-liners, while others fly their entire migrations at speeds approaching 100 kilometers per hour (or more than 60 mph). Future research will continue to elucidate what makes it possible for shorebirds to push the boundaries of what humans think is possible. At present, here’s what we know about how they do it:
They Have the Right Shape
Long pointed wings allow shorebirds to efficiently carry heavy loads, while a long, sleekly shaped body helps them minimize drag while in the air. This aerodynamic design allows shorebirds to fly at high speeds while migrating, enabling them to travel long distances while maintaining their heading in the face of crosswinds that threaten to blow them off course. Shorebirds’ body shapes may also enable them to climb to high altitudes more easily, where they can avoid high air temperatures and find favorable tailwinds.
They Build Up Fat Stores
Unlike humans, birds rely predominantly on fat to power their endurance exercise. Fat holds significantly more energy per unit than carbohydrates. Before departing on their migration from Alaska to New Zealand, Bar-tailed Godwits more than double their body weight. Most of that added weight comes in the form of fat, which comprises up to 55 percent of a departing godwit’s mass.
They can Fly While They Fast
Bar-tailed Godwits burn about a calorie over every 3 km of flight, but they don’t add back any calories over their 12,000-km flights—fasting for the entire two weeks of their fall migration. Upon arrival in New Zealand, the Bar-tailed Godwits weigh about half of what they did when they departed Alaska, as they have burned through nearly all of their fat.
They’re Incredible Body-Builders
Because they grow so heavy for their migrations, shorebirds also need to bulk up their flight and respiratory muscles to help carry all that weight and pump blood to supply all of the extra tissue. Bar-tailed Godwits nearly double the size of their pectoralis (breast) muscles, as well as the size of their heart and lungs. To accommodate their musclebound migratory physique, shorebirds shrink the organs they don’t need, reducing the size of their stomach and gizzard prior to departure.
What Would It Take for a Human to Measure Up?
Cyclists competing in the Tour de France burn more than 8,000 calories per day in order to maintain metabolic rates five times higher than their base metabolic rates. Bar-tailed Godwits migrating from Alaska to New Zealand must be able to maintain metabolic rates more than nine times higher than their basal rates for over nine days. In order to duplicate the feats of these migratory shorebirds, cyclists would have to nearly double that energetic output—and do so without food or water. The average professional cyclist weighs 160 lbs and maintains 2 to 3 percent body fat. Were they to prepare for a Bar-tailed Godwit’s migration, they would need to put on more than 160 additional lbs, of which at least 126 lbs would need to be fat. Can you imagine a 320-pound cyclist (the size of former NFL defensive lineman William “The Refrigerator” Perry) pedaling through the French Alps?