Who actually enjoys long-haul flights? One seabird seems to – the ancient murrelet. It travels almost 8000 kilometres across the north Pacific, then does the whole slog again in reverse, for no obvious benefit. Most migrating birds travel long distances from north to south, or vice versa, to spend the harsher winter in warmer climates, often crossing the equator. Some travel from east to west, to areas where they can get more food.
But the ancient murrelet is unique, criss-crossing the Pacific to move between areas of similar climate. Some of them breed in western Canada and then winter in seas between Japan, China and Korea, before heading back to Canada – the only bird known to cross the full width of the North Pacific. The ancient murrelet is, Gaston says, a rather obscure and not well studied seabird. A member of the auk family, which also includes puffins and guillemots, it mainly breeds in the Haida Gwaii archipelago off the coast of British Columbia.
Gaston and his colleagues used geolocator tags to study the migration of ancient murrelets in 2013 and 2014. They managed to recover data from three of the geolocators and found that the birds had slowly crossed the North Pacific from July to November, travelling from Haida Gwaii to Japan. “I don’t know of any other bird that covers such a long distance from east to west,” says Gaston, “especially when it winds up in waters that are very similar to those it just left.”
Then in February, they set off back to Haida Gwaii, rapidly covering almost the whole distance within a month – the longest migration of any bird in the auk family. This is also twice as far as the longest cross-Atlantic migrations undertaken by Brünnich’s guillemot, which cover 70 degrees of latitude compared with murellets’ 105 degrees, Gaston’s team says. This means they travelled some 270 kilometres per day, probably flying 4 to 5 hours a day.
Gaston is not sure why their outward journey was slower, though he speculates it could be down to moulting hampering flight. There is no obvious reason for the birds to leave North American waters, which support many other seabirds over winter, for the equally temperate Japan. Genetic evidence suggests that the ancient murrelet originated from Asia and has only recently colonised North America, says Gaston. So the ancient murrelet could now be retracing the route by which the species colonised America from Asia. “There doesn’t seem to be any other suitable explanation,” Gaston says.
Journal reference: Ibis, DOI: 10.1111/ibi.12300
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https://www.newscientist.com/article/dn28018-bird-flies-16000-kilometre-pacific-circuit-for-no-clear-reason/ Original web page at New Scientist