Ex-situ avian sex skews: determinants and implications for conservation

With over half of all avian species in decline globally, zoo-based recovery programs are increasingly relied upon to save species from extinction. The success of such programs not only rests with political will, but also in our understanding of species' breeding biology and how individuals and populations respond to changes in their environment. Sex skews, that is, an imbalance in the optimal number of males to females, is an underlying mechanism of population decline in some threatened species. Ex-situ (i.e., zoo-based) management practices will need to become more efficient to support the growing number of conservation reliant species and manage sex skews to amend, repair and restore population stability both in- and ex-situ. In this article, we analysed data from over 182,000 birds in global ex-situ collections. We interpreted sex ratio variation by observing the proportion of males within and between orders, International Union for Conservation of Nature (IUCN) threat status and housing inside and outside of a species' natural range. Overall, our results showed that male-biased sex skews are more prevalent ex-situ than they are in the wild and although they vary greatly at the institutional level, were closer to parity at a global level. The variation amongst threat status and housing outside of range were less significant. These findings have implications for the conservation management of threatened birds and the potential of ex-situ populations to function with maximum effect in an integrated management system.