Muttonbirds lead scientists on 64,000km Pacific tour

The sooty shearwater, or muttonbird.

It's an epic journey for a small bird.

A team of scientists from New Zealand, the US and France has found that sooty shearwaters (titi or muttonbirds) make a 64,000km round trip each year, the longest migration recorded via electronic tracking.

Chasing summer across the Pacific, each bird travels an average of about 64,000km in 200 days, covering up to 910km a day, and dives to depths of 68m for food, said Paul Sagar, seabird biologist at the National Institute of Water and Atmospheric Research (Niwa).

Sooty shearwaters are one of the world's most abundant seabirds but are declining. Populations off the coast of California have dropped dramatically.

Following the bird's annual migration could help to shed light on the causes of the decline, which scientists think could be linked to climate change and entanglement in fishing gear.

Tracking a bird that spends 90 per cent of its time at sea wasn't easy but recent developments in technology allowed scientists to follow birds as small as sooty shearwaters, which are about the size of a small seagull.

The team used light-sensitive electronic tags to follow 19 sooty shearwaters from breeding colonies on Whenua Hou (Codfish Island), near Stewart Island, and Mana Island off Wellington.

The tags used light and temperature to record each bird's location every day over several months.

All the tagged birds followed a figure-of-eight pattern across the Pacific, crossing between Southern and Northern Hemispheres in pursuit of an endless summer.

Instead of roaming the north Pacific as scientists had thought, the birds remained in one of three areas off Japan, Alaska or California.