Understanding the demography of a reinforced population: Long-term survival of captive-bred and wild-born houbara bustards in Morocco

Abstract

Translocation of captive-bred animals to reinforce threatened populations is widely used as a conservation strategy for small and declining wildlife populations. A fundamental goal of these interventions is that translocated animals will survive and improve the future viability of populations. To evaluate this goal, we need to estimate the long-term survival of both captive-bred and wild-born animals in reinforced populations in order to best assess the relative contribution of translocated individuals to population growth. Here, we used tracking data from a large-scale, long-term translocation program in Morocco to estimate long-term survival in a reinforced population of houbara bustards (Chlamydotis undulata undulata). We estimated annual survival rates of captive-bred and wild-born houbara, and considered sources of individual and temporal variation in survival, including how age-specific rates vary between captive-bred and wild-born birds. Our results reveal key differences in how survival varied with age between captive-bred and wild-born houbara. Survival of wild-born houbara was relatively high and constant beyond the first year of life, while survival of captive-bred birds increased more gradually in early years, approaching that of wild-born individuals in older ages. These results suggest that captive-bred houbara have high potential to contribute to the growth and persistence of houbara populations. Our estimates also highlight the importance of considering sources of individual variation in demographic rates when assessing the contribution of reinforcements to population growth. Finally, these analyses emphasise the need to estimate long-term survival when predicting the future viability of reinforced populations.