SPRING FORWARD
NATHAN COOPER IS DRIVING AS FAST AS HE dares, through murky April twilight along a twisting road with an unsettling number of pedestrians, free-range chickens, loose dogs, and feral cats. The grandly named Queen’s Highway is a narrow, unmarked strip of potholed macadam that runs the 48-mile length of Cat Island. We need to be at the southern end by sunrise, and we’re late.
Cat Island is well off the main tourist drag in the Bahamas. Shaped like a long, narrow fishhook, it covers just 150 square miles and is so slender that for much of its length it’s only about half a mile wide. Cat is largely flat and featureless, a lot of dry scrub forest bisected by few roads, with barely 1,500 residents. Slash-and-burn farming, raising goats, or fishing for conch are among the only options here.
But what makes Cat Island a tough place for people—its hot, dry climate and hardscrabble soil, the scrubby forest full of highly toxic poisonwood trees, even its herds of ravenous goats—makes it arguably the best wintering spot in the world for the endangered Kirtland’s Warbler. Perhaps a thousand of these half-ounce birds, fully one fifth of the global population, migrate to this relative speck of land. And it’s why Cooper, a post-doctoral fellow at the Smithsonian Migratory Bird Center in Washington, D.C., has returned to the Caribbean with his crew for a third winter. They are capitalizing on the warbler’s unique biology to learn how the effects of wintering ground conditions shape the lives of migratory birds.
Scientists once thought of winter as a respite for a migratory bird, an easy-living, tropical hiatus from the serious work of migration and reproduction. But they’re learning that a bad winter can cast a very long shadow, an ecological hangover that can linger for many months and across thousands of miles. Sparse rain and limited food in a bird’s winter habitat can create a caloric deficit that delays the start of its migration and may even force it togrounds to find ideal conditions, those shortages can sabotage breeding success. Given that the tropical regions on which hundreds of millions of migratory birds depend are already warming and drying—a trend that is expected to accelerate—this discovery has ominous implications at a time when migrant populations are already in steep decline.
