NEW ZEALAND: THE BAR-TAILED godwit, a plump shore bird with a recurved bill, has blown the record for non-stop muscle-powered flight right out of the sky.
A study published yesterday reports that godwits can fly up to 11,654km without stopping in their annual autumn migration from Alaska to New Zealand. The previous record, set by eastern curlews, was a 6,400km trip from eastern Australia to China.
The birds flew for five to nine days without rest. A few landed on South Pacific islands before resuming their trips, which were monitored by satellite in 2006 and 2007.
As a feat of sustained exercise unrelieved by sleeping, eating or drinking, the godwit's migration appears to be without precedent in the annals of vertebrate physiology.
"The human species doesn't work at these levels, so you just have to sit back in awe of it all," said Robert Gill, a biologist with the US Geological Survey, who headed the study.
The birds were expending energy at eight to 10 times the rate they do at rest. The previous record for a boost in energy output is seven times the "basal metabolic rate."
Peak output in human beings, achieved by Tour de France bicyclists, is a six-fold increase.
"What this suggests to me is that we haven't yet mined the depths, we really don't know what the extremes are," said Kimberly Hammond, a physiological ecologist at the University of California but not involved in the research.
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 non-stop 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 at a time when they are probably somewhat immune-suppressed. It also would add weeks to the trip and itself take energy. So, all in all, flying non-stop 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.
The study is published in Proceedings B,a journal of the Royal Society.
Gill and his colleagues outfitted 23 bar-tailed godwits with satellite transmitters that periodically sent a signal detected by a satellite.
Nine of the transmitters functioned well enough on the southward flight to provide evidence of sustained, non-stop flight.
One female flew directly from the Yukon-Kuskokwim delta of Alaska to New Zealand in eight days. Other birds either landed short of their destination in the Solomon Islands and Papua New Guinea, or the signal was lost near those places.
Four were later identified in New Zealand by leg bands.
The birds weigh no more than 1.5lb when they leave. Half of that is fat, which they burn off completely during the flight.
The birds leave from late August to late September, departing only with favourable tail winds.
How much of their journey is wind-aided is something the researchers hope to determine by overlaying the birds' routes with day-by-day meteorological data.
A major mystery is how high the birds fly. Gill said that since word of his research has spread, researchers on boats in the Pacific have told him of seeing godwits 3,000ft high and "smoking by at deck level".
- (Los Angeles Times-Washington Post service)