In 1976, the biologist Robert E. Gill Jr. came to the southern coast of Alaska to survey the birds preparing for their migrations for the winter. One species in particular, wading birds called bar-tailed godwits, puzzled him deeply. They were too fat. ‘They looked like flying softballs, said Mr. Gill. At the time, scientists knew that bar-tailed godwits spend their winters in places like New Zealand and Australia. To get there, most researchers assumed, the birds took a series of flights down through Asia, stopping along the way to rest and eat. After all, they were land birds, not sea birds that could dive for food in the ocean. But in Alaska, Mr. Gill observed, the bar-tailed godwits were feasting on clams and worms as if they were not going to be able to eat for a very long time. ‘I wondered, why is that bird putting on that much fat? he said. Mr. Gill wondered if the bar-tailed godwit actually stayed in the air for a much longer time than scientists believed. It was a difficult idea to test, because he could not actually follow the birds in flight. For 30 years he managed as […]