Individual traits influence survival of a reintroduced marsupial only at low predator densities

Predation is a key factor contributing to the failure of reintroductions of vertebrates but there is variation in predation risk between individuals. Understanding the traits that render some animals less susceptible to predation, and selecting for these traits, may help improve reintroduction success. Here, we test whether prior exposure to predators or specific morphological and/or behavioural attributes explained variation in post-reintroduction survival in a moderate and low predator density environment. We exposed a population of the threatened burrowing bettong (Bettongia lesueur) to controlled densities of feral cats (Felis catus) for ≥3 years. We then conducted two translocations of cat-exposed and control populations that had no exposure to predators to a new site where cats were present at moderate, then low density. Variation in survival of burrowing bettongs was not explained by prior predator exposure to predators or measured individual traits at moderate cat density. At lower cat densities, males died sooner and burrowing bettongs with larger hind feet survived longer. Although prior cat-exposure did not confer a survival advantage at low cat densities, the cat-exposed burrowing bettong population had larger hind feet (n = 44) compared to the control population (n = 45) suggesting that trait divergence between cat-exposed and non-cat-exposed burrowing bettongs may not yet be sufficient for improved survival. Alternatively, prior predator exposure may not confer a survival advantage because they are “outgunned” by evolutionarily novel cats. Predation is a major problem thwarting successful reintroductions world-wide. Exposing populations to predators over longer time periods and periodically testing survival will be required to determine whether pre-release predator exposure prepares animals for life with novel predators. Our study highlights the importance of reducing predator activity at release sites prior to reintroduction to enable any benefits from intraspecific variation in survival traits to be realised.

H.L. Bannister, M. Letnic, D.T. Blumstein, K.E. Moseby