Evolutionary theory predicts birds should adjust the sex ratio of their broods in response to external factors that differentially affect the reproductive value of each sex. We examined the brood sex ratio in the Lilac-crowned Parrot (Amazona finschi) in relation to climate, hatching date, and hatching order. We used polymerase chain reaction amplifications to identify the gender of 66 nestlings from 32 clutches spanning 7 years. There was a tendency to produce more female offspring in years of high nestling survival following high rainfall with a slight female-bias in third-hatched nestlings. We found no significant associations between brood sex ratio and rainfall, hatching date, or hatching order within clutches. Our results suggest the examined factors provide insufficient differential costs or benefits of offspring gender to promote sex ratio bias in this monomorphic species.
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Vol. 124 • No. 2