Variation in the Size and Shape of Darwin's Finch Eggs

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Abstract
Egg size and shape variation was analyzed in 10 spp. of Darwin''s finches [ground finches: Geospiza magnirostris, G. conirostris, G. scandens, G. fortis, G. fuliginosa and G. difficilis; tree finches: Platyspiza crassirostris, Cactospiza pallida and Camarhynchus parvulus; and the warbler finch: Certhidea olivacea]. Egg shape varies among species: eggs of the tree finches are relatively long, those of the warbler finch are relatively short and eggs of the ground finches are intermediate. G. conirostris is unusual among the ground finches in laying eggs of similar shape to those of tree finches. These variations parallel to some degree the variation in egg shape among ecologically similar groups of species in continental regions. Egg size and adult body size are positively correlated, intraspecifically and interspecifically. Darwin''s finches, especially the larger species, lay relatively small clutches of small eggs in terms of egg or clutch weight in proportion to adult weight. They also have short incubation periods. These are adaptations which enhance repeated and rapid breeding at irregular intervals.