Rafting behaviour of Yelkouan shearwater Puffinus yelkouan breeding at Rdum tal-Madonna, Malta

Abstract

The Yelkouan Shearwater Puffinus yelkouan is listed as Near Threatened under the IUCN Red List (IUCN 2010). Malta holds internationally important breeding populations of this species, with between 1,660 and 1,980 breeding pairs, equating to approximately 10% of the world population (Borg et al. 2010). The largest colony in the Maltese islands is found at Rdum tal-Madonna, in the north-east of Malta, which is designated as a Special Protection Area (SPA) for this species. As this area holds over one-third of the Maltese population, the site has been the subject of a four year EU LIFE project, focussed on the conservation of the species on land and at sea. As part of the project, intensive work was carried out using a range of telemetry techniques to ascertain important marine areas for this species. This paper examines one aspect of this research – the identification of rafting areas for Yelkouan Shearwater during the breeding season, specifically birds nesting at the colony located at Rdum tal-Madonna in the north of the island. In Malta, Yelkouan Shearwaters begin returning to their nesting sites in October, with egg-laying beginning in March. Chicks hatch in late April and by late July the last juvenile birds have fledged (Borg et al. 2010). Rafting behaviour is common amongst shearwaters during the breeding season, with adult birds often forming large aggregations in the waters near to their colonies in the hours before darkness prior to returning to their nest sites. It is not clear why these birds form rafts and some scientists have hypothesised that this behaviour may have developed to reduce the chances of predation of birds returning to nest sites, with the birds remaining in their rafts until nightfall and the cover of darkness (Klomp et al. 1992). Alternatively, it could be because birds which are away for several days at distant food sources cannot time their returns precisely, so assemble to wait until it is safe to return to the nests in groups (Warham 1990). Rafts of Cory‟s Shearwaters Calonectris diomedea offshore from colonies in Malta can be very large, with the rafts of this species off Ta Cenc (one of the largest colonies) often numbering in the 1,000s in summer (Bonavia et al. 2005). Rafts of Yelkouan Shearwaters tend to be smaller and less obvious than those of the Cory‟s Shearwater. Consequently, they are often overlooked and limited data is available. This paper considers data collected from data loggers on the location of rafting sites for Yelkouan Shearwaters breeding at Rdum tal-Madonna prior to returning to their nest sites after nightfall. Rafting sites at other times of the year or for other reasons, such as prior to the breeding season, at offshore feeding sites, or in the post-breeding season moulting period are not included here.