The more we learn about bird migration, the more bizarre it gets. If you’re at all interested in birds, or in animal behavior, get your tuchus over to The New York Times and read Carl Zimmer’s nice piece on how recent technological advances, like the invention of tiny geolocators, have produced surprising new results about migration. A few snippets:
Just as he had suspected, the bar-tailed godwits headed out over the open ocean and flew south through the Pacific. They did not stop at islands along the way. Instead, they traveled up to 7,100 miles in nine days — the longest nonstop flight ever recorded. “I was speechless,” Mr. Gill said. . .
Consider what might be the ultimate test of human endurance in sports, the Tour de France: Every day, bicyclists pedal up and down mountains for hours. In the process, they raise their metabolism to about five times their resting rate. The bar-tailed godwit, by contrast, elevates its metabolic rate between 8 and 10 times. And instead of ending each day with a big dinner and a good night’s rest, the birds fly through the night, slowly starving themselves as they travel 40 miles an hour. . .
In fact, ruby-throated hummingbirds returning north in the spring will set out from the Yucatán Peninsula in the evening and arrive in the southern United States the next afternoon. .
Mr. Gill and his colleagues have recorded similar odysseys from other wading birds, using satellite transmitters. They found that bristle-thighed curlews fly as far as 6,000 miles without a stop, traveling from Alaska to the Marshall Islands. They have also recorded whimbrels flying 5,000 miles nonstop from Alaska to Central America. . .
By the time the birds are ready to leave, their bodies are 55 percent fat. In humans, anything more than 30 percent is considered obese. But as soon as the birds are done eating, their livers and intestines become dead weight. They then essentially “eat” their organs, which shrink 25 percent. The birds use the proteins to build up their muscles even more.
And the weird thing is that we have no idea how the birds find their way.
Fig. 1. A geolocator. Weighing less than 1.5 grams, it can track a bird’s position by monitoring ambient light levels.
Fig. 2. A juvenile shrike wearing a geolocator. From Ontario Field Ornithologists.