Primary Molt and Transequatorial Migration of the Sooty Shearwater

• Published in: The Condor (Los Angeles, Calif.) Calif.), 1991-08, Vol.93 (3), p.724-730
• Main Authors: Cooper, John, Underhill, Leslie G., Avery, Graham
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Aviculture; Biological and medical sciences; Bird banding; Birds; Breeding; Data types; Feathers; Fundamental and applied biological sciences. Psychology; Marine; Molting; Oceans; Petrels; Puffinus griseus; Sea birds
• ISSN: 0010-5422; 1938-5129
• DOI: 10.2307/1368204

Examination of beached corpses of 244 Sooty Shearwaters (Puffinus griseus) from the southwestern Cape, South Africa, showed that simple descendent primary molt occurs from December to June, with most records being in the months of February and March. Based on percentage feather mass grown, primary molt takes a mean of 159 days for completion, with mean estimated starting and completion dates of 2 January and 10 June. Because the completion of breeding extends from late March to early May, the birds studied cannot have bred successfully in the previous austral summer and were probably prebreeders. Unlike the situation in the North Pacific Ocean, Sooty Shearwaters in the North Atlantic Ocean do not undergo primary molt. The hypothesis that Sooty Shearwaters of breeding age migrate preferentially into the North Pacific, whereas young birds first molt in the South Atlantic Ocean before migrating into the North Atlantic, needs to be tested by extensive banding of birds at the breeding localities.