Birds like the bar-tailed godwit have found places like the coast of Alaska where the supply of food is high and predators are scarce. By flying over the open ocean, they continue to avoid predators. They may also reduce their odds of picking up a parasite from another bird.
Their destinations are also safe enough for them to recover. Bar-tailed godwits that arrive in New Zealand face no predators, and so they can simply rest. “They just look exhausted. They’ll land and just go to sleep for several hours before they do anything else,” Mr. Gill said.
Unfortunately, some of the habitats on which these endurance champions depend are under serious threat. In the Delaware Bay, for example, fisherman are scooping up horseshoe crab eggs, which birds like the red knot travel thousands of miles to eat. When bar-tailed godwits return to Alaska in the spring, they make one stop along the coast of China and Korea, a favorite spot for many other migrating birds. The coastal wetlands there are disappearing fast, and many migrant birds are in decline.
“I hope we have these birds to study 100 years from now,” Dr. Piersma said. “But sometimes I wonder.”