Does feeding zone influence egg size in slow-breeding seabirds?

Abstract

In several bird species, mothers that endow their eggs with additional resources benefit from more rapid development and more robust offspring. We examined egg size and associated life-history traits in 44 species of the slow-breeding procellariiform seabirds (albatrosses and petrels). The far distant foraging of some of the species should subject them to difficult ecological conditions and perhaps delays in return to the nest. Such delays might lead to poorer egg care by the remaining parent. To compensate, we predicted a positive association of egg size with foraging zone (offshore, near pelagic, far pelagic), and both with the length of incubation shifts. We tested this hypothesis and also examined egg size and fitness-related reproductive traits. Egg size scaled significantly and tightly with female body mass (β = 0.72, R2 = 0.98). After influences of both size and phylogeny were removed, however, egg size was positively and significantly associated with both mean length of incubation shift and feeding zone (r = 0.45 and 0.46, respectively), perhaps indicating a life-history syndrome of egg size, incubation, and distance that species go to forage during the breeding season, and supporting the compensation hypothesis.