Abstract
Translocation of captive-bred individuals to reinforce wild populations may be an important conservation approach for some species, but can be detrimental when employed to boost exploited wild populations, particularly where repeated long-term reinforcement aims to compensate for repeated unregulated offtake. We review evidence that captive breeding alters multiple physiological, life-history and temperamental traits through founder effects, genetic drift and unintended adaption to captivity; degrades learnt behaviours; and compromises biogeography, population structure and viability through introgression. We highlight these risks for the globally threatened African houbara Chlamydotis undulata and Asian houbara C. macqueenii, 2 bustard species hunted throughout much of their ranges and now subject to multiple large-scale captive-breeding programmes and translocations. In eastern Morocco, annual releases of captive-bred African houbara are 2‒3 times higher than original wild numbers, but no investigation of their potentially deleterious effects has, to our knowledge, been published, although most wild populations may now have been replaced by captive-bred domestic stock, which are reportedly not self-sustaining. Despite multiple decades of reinforcement, we are not aware of any analysis of the contribution of captive breeding to African houbara population dynamics, or of the genomic consequences. Asian houbara release programmes may also be promoting rather than preventing declines, and need to contextualise themselves through rigorous analyses of wild population numbers, demographic rates and threats, maintenance of phylogeographic concordance of released with supplemented populations, profiling of traits crucial to survival and the measurement and modelling of the impacts of reinforcement on physiological and behavioural fitness of wild populations.
Highlights
Captive breeding is an increasingly common component of wildlife conservation programmes worldwide (McGowan et al 2017), helping prevent the extinction of many species (Bolam et al 2021)
Birds benefiting from ex situ programmes include the bearded vulture Gypaetus barbatus in Europe
IUCN guidelines stipulate that conservation releases should not take place until the cause of the original extinction or population decline has been addressed (IUCN/SSC 2013), and the success of such releases is commonly defined as the establishment of a population able to persist without further intervention (Griffith et al 1989, IUCN/SSC 2013)
Summary
Captive breeding is an increasingly common component of wildlife conservation programmes worldwide (McGowan et al 2017), helping prevent the extinction of many species (Bolam et al 2021). If offtake is not regulated to sustainable levels, continuous captive-breeding reinforcement can itself become a conservation issue, where it involves species of conservation concern We suggest this is the case with 2 threatened bustards, African houbara Chlamydotis undulata and Asian houbara C. macqueenii. The African houbara occupies semi-desert lands from northernmost Mauritania to Egypt west of the Nile (BirdLife International 2020b), while the Asian houbara is a resident breeder in semi-deserts from the Arabian Peninsula and Middle East to southern Iran and Pakistan and a migrant breeder from Central Asia to western China, wintering in the same general range as the resident populations (Combreau & Al Baidhani 2013, BirdLife International 2020a) (Fig. 1) For many centuries, both species were the prized avian quarry of Arab falconers, occupying a central place in the culture of the desert peoples of the Middle East (Bailey et al 1998). We review the potential risks inherent in such programmes, when used for game reinforcement, and assess the degree to which this approach can be considered an appropriate response to the plight of the 2 species of houbara
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