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.