David M. Larson
Willow Warbler. Photograph by Mike Prince (CC BY 2.0).
In the bird world, it takes at least two to tango. Ratios of males to females in breeding populations may vary for a variety of reasons, even if there is equal probability of hatching in male and female. Often sex ratios are male-biased, especially in declining or small populations. There have been relatively few studies of the causes and consequences of male-biased breeding populations in bird species.
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