In early February, Yelkouan Shearwaters come to land and couples meet inside their nests to mate. Afterwards, they fly back out to sea where females spend two or three weeks feeding to gain nutrients for egg development. All shearwaters and petrels perform this trip called a ‘pre-laying exodus’. Once they have feasted on small fish and squid, diving to a depth of 30m, they then return to their burrow to lay their egg and the males take the first shift of incubation. In February and March 2016 the project team have been in the field to find out more about the pre- laying period of Yelkouan shearwaters. We wanted to investigate the movements of the females and males during this period and were keen to discover their main feeding sites.
More than 20 adults from two important colonies in Malta were fitted with GPS loggers during the mating period in early February. Later the loggers were retrieved when the females came back to lay their eggs in late February and early March. When we recaptured the females on the way into their nest to lay we could feel the large single egg swelling their abdomen.
With our small study we proved that Yelkouan Shearwater females perform a pre-laying exodus spending around 17 days out at sea south of Malta, visiting an area off the coast of Libya which is believed to be rich in pelagic fish such as sardines. We also discovered that during the same period the males are out at sea but they come back regularly to keep the nest occupied and stop other couples from taking over.
For the first time we could show that the Yelkouans’ choose to prepare for egg laying, a crucial period in the life-cycle of these birds, feasting in the productive waters off North Africa. Our results highlight the importance of cooperation between countries in the Mediterranean Basin to effectively protect these threatened seabirds and the areas where they feed.