A World on the Wing by Scott Weidensaul

Author:Scott Weidensaul [Weidensaul, Scott]
Language: eng
Format: epub
Published: 2021-02-16T00:00:00+00:00

Hudsonian godwits, which form a few widely scattered populations in the Arctic and subarctic, follow similar routes to and from South America, but diverge in spring in the Great Plains—where they diverge as well in how they are faring in the face of climate change.

The Chilean birds swing northwest, making a largely unbroken flight to south central and western Alaska, arriving the last week of April or the first week of May. The godwits that Nathan studied in this group, breeding along the Beluga River west of Anchorage, now arrive about nine days earlier than they did 40 years ago. But they suffer no mismatch, because the climate all along the route on which they fly, and at their end point in Alaska, has warmed at a fairly smooth, consistent rate, allowing them to accelerate their timing to keep pace with the seasonal changes. Their chicks hatch just in time to catch the insect wave, and the population is thriving.

Not so the godwits that started in Argentina. They arrive on their staging grounds in the Plains a few weeks behind the Alaskan birds, and after feeding and resting there they fly another 2,000 miles north to Hudson Bay, arriving the last week of May or early June—about 10 days later than they once did. Why? Because climate changes occur in paradoxical ways, and the Hudson Bay godwits are experiencing seasonal whiplash.

“On the northern portion of their migration route, the Dakotas and prairie provinces up to Hudson Bay, conditions are actually cooling,” Nathan told me. That’s part of the global weirding that is climate change; some parts of the planet are getting colder, at least for now, and at certain times of the year. Snow and ice now linger later in this final section of the godwits’ route, preventing the migrants from pushing north as early as they once did. And it gets worse. “The unfortunate thing is that those cooling conditions in May are counteracted by really warming conditions the rest of the summer—June and July are experiencing some of the most drastic warming” anywhere in the North, he said. As a result, the godwits have to delay their arrival on their breeding grounds and so get a later start at nesting—but the rapid warming still brings out the insect swarms too early. Instead of reaching a peak just as the growing chicks need the most food, the bugs top out too soon, leaving the older chicks underfed right when their energy demands are highest, a seasonal mismatch reminiscent of the pied flycatcher’s.

“So the godwits are between a rock and a hard place,” he said. “They can’t arrive any earlier or else they’re going to encounter a lot of snow. But if they arrive any later, they’re going to be even more mismatched with the emergence of the bugs their chicks rely on for food.” The result? Many years the godwits are unable to breed successfully, with just 6 percent of their chicks making it to adulthood. Recent research, by

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