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Molt in Leach's and Ashy Storm-Petrels

1976; Wilson Ornithological Society; Volume: 88; Issue: 1 Linguagem: Inglês

1938-5447

David G. Ainley, T. James Lewis, Steve Morrell,

Animal Vocal Communication and Behavior

Broadly speaking, a bird's major energy-demanding activities during the yearly cycle are reproduction, molt, and in migratory species, migration. In many species, these activities do not overlap, presumably because of energy demands they each place upon a bird. Of particular interest to us are some species in the family Hydrobatidae. Harris (1969) felt the extended period required for molt in certain tropical storm-petrels prevents them from engaging in less-than-annual nesting cycles even though they are present in an environment that allows such regimes in other sympatric marine bird species. If molt can have such a governing effect on the energy budgeting of hydrobatids, its processes in this group should be of interest. Molt is relatively well known for only 6 storm-petrels-British, Hydrobates pelagicus: Scott (1970); Wilson's, Oceanites oceanicus: Roberts (1940), Beck (1970), Beck and Brown (1972); Harcourt's, Oceanodroma castro: Allen (1962), Harris (1969 ); Leach's, Oceanodronta leucorhoa: Harris (1974); Galapagos, Oceanodroma tethys: Harris (1969); and White-faced, Pelagodroma marina: Mayaud (1950), Browne in Palmer (1962)-but this information, with the exception of that for H. pelagicus, is confined largely to defining the extent of overlap among molt, nesting, and migration or post-breeding dispersal. In an earlier paper (Ainley et al. 1974), we compared the life-histories of 2 species, the Leach's and the Ashy Storm-petrel (0. homochroa), that breed on the Farallon Islands, California. These 2 morphologically similar species were found to be similar in a few but different in most aspects of their life histories. In brief, Leach's Storm-petrels visit the Farallones for 7 months from late February to early September, and winter during intervening months in the tropical and subtropical waters of the eastern Central and North Pacific. They lay eggs during a 5?/ week period from early May to mid-June. Ashy Stormpetrels visit the island for most of the year and usually remain within several hours flight of the island during all seasons. They lay eggs from late April to mid-July and sometimes later. We previously made some comparisons on molt (Ainley et al. 1974), explaining that it overlapped the pre-egg and chick stages of the annual cycle much more in the sedentary Ashy than in the migratory Leach's. In the present paper we present the full analysis of our work on the timing, sequences, and rates of molt in these 2 species.