Hello, We present just published study where we have examined the brood sex ratio and offspring body mass in relation to the timing of breeding and brood size in the Great Cormorant (Phalacrocorax carbo sinensis). The brood sex ratio was significantly related to the hatching date, with a decreasing proportion of males in the brood in the course of the season. Moreover, male chicks had significantly lower body mass if they hatched later in the season, whereas there was no such relationship for female offspring. Assuming that environmental conditions deteriorate with progress of the breeding season, and male offspring may be more vulnerable to poor environmental conditionsWe interpreted the decline in the proportion of sons in the brood late in the season as adaptive.
You can find the paper here: http://onlinelibrary.wiley.com/doi/10.1111/ibi.12061/abstract
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