A 7,000-Mile Journey

I have written before about the impressive migratory flights of bar-tailed godwits, which fly nonstop across the Pacific on their way south from Alaska to New Zealand. The results of that telemetry study have now been formally published. An interesting point is why they choose a nonstop overwater flight instead of following the coast of Asia.

As astounding as the feat is the fact that it represents a highly evolved solution to a problem, not a fluke or one-time occurrence.

The nonstop, over-water route is free of predators and substantially shorter than a hopscotching route down the eastern coast of Asia, which is the alternative. Landing and eating -- literally, refueling -- would expose the birds to disease and parasites when they are probably somewhat immune-suppressed. Refueling also would add weeks to the trip and itself take energy.

All in all, flying nonstop across most of the north-south span of the Pacific Ocean is the safest thing to do.

The death rate during the migration is unknown but presumably low, as the population of bar-tailed godwits, estimated at 100,000, has been stable and long-lasting.

"This system would not have perpetuated itself if mortality were a big problem," said Gill, whose study is being published today in Proceedings B, a journal of The Royal Society, in England.

A full report on the project will appear in Proceedings of the Royal Society B. More on the project, including maps and photos, is available from the USGS shorebird research page.