Seabird’s Ocean Lifestyle Revealed

The Manx Shearwater is a seabird that migrates 20,000km from the UK to South America and then back again across the Atlantic Ocean. The birds spend most of the lives at sea and nest in remote locations, only coming ashore at night, so their ocean-going lifestyle has always been something of a mystery.

In two studies the scientists used electronic logging tags to track the Shearwater’s migration and tiny GPS trackers, developed at Oxford University, to map the birds’ long foraging trips. They report their results in papers in Proceedings of the Royal Society B and the journal Ibis.

The results suggest that, during their long migration, all 12 of the birds studied had to make at least one stopover of up to two weeks to ‘refuel’ – behaviour not normally associated with birds that migrate over open seas. They also showed that their migration route takes them further south than had been thought.

'By making stop-overs these 400g birds would not have to carry extra weight, in the form of fat, for the first part of their epic journey as they would if they flew to South America direct,’ said Professor Tim Guilford, from Oxford’s Department of Zoology who led the Oxford team.

The researchers also found that in the two weeks prior to laying their single large egg, female Shearwaters journeyed to distant waters south west of Britain, probably to exploit rich fishing near the continental shelf break. Males stayed nearer their Pembrokeshire colony during breeding: both males and females depend heavily on fisheries within the Irish Sea.

‘In some ways protecting nesting sites on land is easy, what our results shows is that we also need to think about how to protect feeding areas at sea – something which is much more of a challenge,’ said Professor Guilford.

Scientists believe that monitoring wild seabird populations is increasingly important as they are particularly sensitive to environmental change and give an indication of the health of our oceans.

The team included researchers from Oxford’s Department of Engineering Science, Microsoft Research Cambridge, British Antarctic Survey, Skomer Island National Nature Reserve, and the University of Sheffield. The technical development work was supported by Oxford’s John Fell Fund.