Breeding cycle and nestling growth of Bulwer's Petrel on the Desertas Islands, Portugal

The Bulwer's Petrel (Bulweria bulwerii)colony on Deserta Glande, Madeira Ar chipelago, is one of the largest in the Atlantic Ocean. It was studied over six months in 1994 and 1995. Breeding occurs from mid April to early Octob er, as in other colonies in the Atlantic (Azores and Can;ln islands) and Pa cific Ocean (Manana Island and Johnston Atoll). At Desertas, the breeding c hronology is characterized by synchrony both within and between pairs. Sync hrony within a pair affected breeding success, mainly during the laying per iod anti incubation; pairs with both mates present on the laying night and with well-defined incubation shifts had higher hatching success. Parental p erformance in relation to nest choice and preparation also influenced hatch ing success. Breeding success of 74% was similar to that found in Pacific c olonies. Both sexes left the colony on a pre-laying exodus averaging 28 day s. The exodus and the long, well-defined shift system suggest a scarcity of food near Desertas. Data from other colonies are needed for comparison. Ne stling growth was typical of Procellariiformes. The bill and tarsus were mo re developed than the wings at hatching and achieved maximum dimensions wit hin 73% and 81% of the nestling period, while the wings continued to develo p until fledging. Body mass achieved 181% of the adult weight, similar to v alues found on the Pacific Ocean and comparable to values for some Hydrobat idae. Fledging weight was lower on Desertas than on Manana Island.