Inevitable fates? The recovery potential of small populations

Abstract The recovery prospects of species reduced to critically small numbers are frequently seen in a pessimistic light. Even if conservation efforts could successfully tackle drivers of severe decline, small population effects would be expected to inhibit population growth. Accounts of dramatic conservation recoveries seem to challenge this narrative, but without a broader examination encompassing all actions and outcomes, the representativeness of success stories alone is unclear. Here, we conduct an observational study evaluating all 147 bird and mammal species that have been below 50 individuals in the wild at any point since 1950, of which 141 had sufficient elapsed time to assess an outcome. We characterized the history, if any, of conservation action in these species, and used Bayesian multi-level logistic regression to model its association with subsequent population status. Most species subject to direct conservation recovered to at least 100 individuals, with the highest modelled recovery probabilities associated with those subject to a combination of actions to limit external drivers of decline and directly manipulate populations. These findings indicate a striking potential for recovery even in critically small populations and serve as an empirically grounded counterpoint to advocates of abandonment of such species under a conservation triage framework.