EGG SIZE, EGGSHELL POROSITY, AND INCUBATION PERIOD IN THE MARINE BIRD FAMILY ALCIDAE

Abstract

Abstract Although the ultimate factors that influence the duration of avian incubation periods are well known, we know much less about the proximate mechanisms by which birds adjust incubation period in response to selection. We tested the hypothesis that an adjustment in eggshell porosity is one such proximate mechanism (i.e., that avian species with higher ratios of incubation period to egg size lay eggs with less porous shells). Eggshell porosity affects the rate of gaseous exchange between the developing embryo and the external environment; thus, to the extent that embryonic metabolism is diffusion-limited, eggshell porosity could directly determine incubation period. To test that hypothesis, we collected eggs from seven species of Alcidae, a family of marine birds that exhibits an unusual degree of interspecific variation in incubation period, and measured egg mass and eggshell porosity (determined by the number and size of pores and the thickness of the shell). Incubation periods were obtained from ...