Molt-Breeding Tradeoffs in Albatrosses: Life History Implications for Big Birds

Abstract

The general argument of this paper is that incomplete primary molts in large birds may periodically force them to skip a year of breeding to replace worn flight feathers. Laysan and black-footed albatrosses show a unique pattern of incomplete molt in their primaries, together with an unusual pattern of breeding frequency - instead of breeding every year or every other year, they breed some years, and skip other years. We argue that their incomplete molts and unusual breeding frequencies are driven by tradeoffs between the time allocated to molt and breeding, and these tradeoffs develop because of a physiological constraint in the rate at which individual feathers can be generated. We test the hypothesis that Laysan albatrosses do not have time to breed and also replace all ten primaries in the same year. There is substantial variation in the number of primaries replaced in a molt, and this variation correlates both with individual condition and the amount of time a bird has available for molting after breeding is completed. Differences in molt patterns between species, sexes, and age classes also correlate with the time available for molting. Molt-breeding tradeoffs may have long-term consequences on future reproduction, since a year of breeding may need to be skipped to replace the accumulation of worn-out primaries. We make a series of predictions about what these tradeoffs imply for future breeding costs, frequency of breeding, and synchronization of molt within pairs.