Studies of bird migration continue to deliver amazing narratives. This is as true of seabirds as of landbirds crossing the Sahara or the high Himalayas. Witness a recent study reporting the 55,000 km round-trip migration of a modest grey seabird, Stejneger’s Petrel that weighs about 150 g. The remarkable distance is greater than any landbird migration recorded. The species’ entire population, about 100,000 pairs, nests on Isla Alejandro Selkirk in the Juan Fernández archipelago around 700 km west of continental Chile in the eastern Pacific Ocean. Incidentally this archipelago was where the Scottish seaman, Alexander Selkirk, was marooned for four years in the early 1700s. The brouhaha associated with his return to the UK prompted Daniel Defoe to write Robinson Crusoe; hence the current island name.
The study, recently reported in Marine Biology, was undertaken by Tommy Clay, an analyst with the US Environmental Defense Fund and the University of California, Santa Cruz, and Michael Brooke of the University of Cambridge. It involved the deployment of 1g geolocators on the birds in January 2020. These devices detect light levels and hence the time of local dusk and dawn, from which the geographical position of the bird can be calculated. They also give a wet/dry reading, effectively reporting whether the bird is flying, or feeding or resting on the sea.
Stejneger’s Petrel soon to set forth across the Pacific where its movements will be tracked by the tiny geolocator on the left leg.
Fortunately Brooke was able to leave the island before the world closed down for COVID but “I had to plead with the ship’s captain and emphasize that my visa was about to expire and that University students were expecting some lectures. Both were in fact true.” For the next two years, as planned, the birds carried the devices as they voyaged across the Pacific Ocean. The extent of those travels was only revealed when Brooke returned to Isla Alejandro Selkirk in January 2022. That journey was through a thicket of COVID-restrictions that meant travel from Heathrow to the island took five weeks. “But I am glad I made the effort and was able to retrieve the devices from the birds still nesting in the same burrows as two years earlier,” says Brooke.
Clay takes up the story. “While during the pandemic, many of us were extremely restricted in our movements and did not leave our houses for days on end, this small seabird migrated more than 55,000 km each year from Chile to Japan and back across the largest ocean on Earth.”
Figure from Clay & Brooke 2024 a) Migration routes and non-breeding areas of Stejneger’s Petrels tracked with geolocators over two years from Isla Alejandro Selkirk, Juan Fernández Islands (yellow triangle). The outbound and return migrations and non-breeding movements are shown as orange, yellow and green lines, respectively. b-c) The non-breeding movements of two example individuals in both years of tracking (2020: pink, 2021: sky blue) are shown in two separate panels.
After breeding, the northbound migration from the southeast Pacific Ocean was rapid and took birds past the Hawaiian archipelago, covering 13,700 km over 22 days at 640 km/day. Then followed a three month sojourn in the northwest Pacific. Flight activity was much reduced; the birds spent about two-thirds of each day on the water. Birds focussed their activity in an area where colder waters from the north Pacific and warmer water from the subtropics meet and concentrate food such as fish and squid.
At the end of the northern summer the petrels’ return journey to the southern hemisphere did not reprise the northbound route. Rather the birds first travelled south and then, when east of New Zealand, turned left to head towards Chile in the Roaring Forties. This indirect route covered 24,000 km over 51 days at 500km/day. “Such a distinctively triangular ‘circuit’ was a surprise; it has not been recorded for any other species,” comments Brooke.
The study once more reinforces the message that distant regions of the world’s oceans are connected by flyways used by seabirds travelling prodigious distances.
Read the full paper here: Clay, T.A. & Brooke, M. de L. 2024.Trans-equatorial migration links oceanic frontal habitats across the Pacific Ocean: year-round movements and foraging activity of a small gadfly petrel . Marine Biology 171: 60. Doi: 10.1007/s00227-023-04373-3
Tracking data from this study is uploaded as Seabird Tracking Database dataset 1872.