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>In charadriiform birds, recent research has shown clearly that polyandry and sex-role reversal (where males care and females compete for mates) as found in phalaropes, jacanas, painted snipe and a few plover species is clearly related to a strongly male-biased adult sex ratio.[21] Those species with male care and polyandry invariably have adult sex ratios with a large surplus of males,[21] which in some cases can reach as high as six males per female.[22]
>Male-biased adult sex ratios have also been shown to correlate with cooperative breeding in mammals such as alpine marmots and wild canids.[23] This correlation may also apply to cooperatively breeding birds,[24] though the evidence is less clear.[21] It is known, however, that both male-biased adult sex ratios[25] and cooperative breeding tend to evolve where caring for offspring is extremely difficult due to low secondary productivity, as in Australia[26] and Southern Africa. It is also known that in cooperative breeders where both sexes are philopatric like the varied sittella,[27] adult sex ratios are equally or more male-biased than in those cooperative species, such as fairy-wrens, treecreepers and the noisy miner[28] where females always disperse.
hmmmmm
