Diet, maternal condition, and offspring sex ratio in the zebra finch, Poephila guttata

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Abstract
Where maternal condition affects condition and reproductive potential of offspring differentially with respect to sex, mothers in relatively good condition should produce more of the sex whose fitness is more dependent on condition. We experimentally manipulated body–condition in unmated zebra finches by feeding them for three months on high– or low–quality diets. Birds were then allowed to breed, while keeping the same diets. Females on the lower quality diet were in better condition and hatched significantly more males than females. Poorer condition females hatched an equal sex ratio. Chicks fed on the low–quality diet, but not on the high–quality diet, showed female–biased mortality. These results show that facultative sex ratio manipulation and sex–biased mortality can act together to produce extreme sex ratios in this vertebrate.