Shearwaters take 'single sex' summer holidays

Balearic Shearwater

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Balearic shearwaters take "female only" migrations to France over the summer, say scientists.

Migratory societies may be segregated, with females also spending longer on migrations, a study found.

Europe's only critically endangered seabirds are frequent visitors to UK waters, but there are only an estimated 3,200 breeding pairs.

It is the first time scientists have succeeded in tracking the year-round, at-sea movements of the birds.

A team of researchers from the University of Oxford, together with the National Oceanography Centre, the British Geological Survey and local experts in Mallorca, Spain carried out the study.

Find out more:

  • Balearic shearwaters are frequent visitors to UK southern coastal waters
  • Accidental catching during fishing is thought to be the species' greatest threat away from land
  • The birds rest on the water and plunge-dive for food

Balearic shearwaters spend most of the year close to their breeding colonies in caves along the coasts of the Spanish Balearic Islands.

At the end of June the birds make a three-month migration out of the Mediterranean to feed in the waters along the Atlantic coasts of Iberia and France.

After tagging 26 birds from a colony in Mallorca in 2010 with miniature geolocation devices, the research team tracked migrating birds to two relatively small areas off west Portugal and southwest Brittany.

The results were published in the journal PLoS ONE.

They found that only females migrated to southwestern Brittany, suggesting that male and female Balearic shearwaters may head for different migration "hotspots" over the summer period.

The study also found that females may spend longer on migration than males - with the median duration of a trip away 91 days for females and 83 days for males.

Even the females that did not travel as far as southwest France spent longer on migration than males, indicating that the more distant destination was not the cause of the longer period away.

The Oxford team is using the findings to inform conservation measures for Balearic shearwaters.

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