Extended laying period by the European Storm-petrel Hydrobates pelagicus melitensis on Filfla island

Abstract

Most members of the Order Procellariiformes breed once a year with many colonial nesting species being highly synchronous in their breeding cycle (Warham 1990). Some tropical species such as the Madeiran Storm-petrel Oceanodroma castro have extended laying periods with two cycles of laying (Snow & Snow 1966). Observations carried out in the last sixteen years (1990-2006) have shown that the Mediterranean European Storm-petrel Hydrobates pelagicus melitensis breeding on Filfla Island also undergoes an extended laying period. The storm-petrel is a common breeding visitor to the Maltese Islands reported as breeding in large numbers among the boulder and rubble scree of Filfla Islet (Sultana & Gauci 1982). A small colony of over 25 pairs was discovered in a cave in Gozo (Borg & Sultana 1992-94) while evidence of breeding has also been noted in another nearby cave in the summer of 2006 (pers.obs). In the last three years there have also been regular sightings of this species during the breeding season at Rdum tal-Madonna on mainland Malta (Borg et al. 2010). Filfla, which is situated about 5km south of Malta, holds the largest known storm-petrel colony in the Mediterranean with an estimated 5,000-8,000 breeding pairs breeding in the boulder and rubble scree that surrounds the islet (Massa & Sultana 1993, Borg & Sultana 2000). Erosion and weathering are causing dramatic changes to the topography of the island resulting in reduced breeding areas for the storm-petrels. Night visits to Filfla have always been carried out from May and September due to strong winds and rough seas, which prevented researchers from visiting the island from February to April. The majority of the birds have been handled during mist-netting sessions. A small number of study areas were identified but because of the rugged terrain it was difficult to locate significant numbers of incubating birds.