Behavioural, morphological and dietary response of rabbits to predation risk from foxes

We report on the responses of wild European rabbits (Oryctolagus cuniculus) to a reduction in predation risk from red foxes (Vulpes vulpes) in a predator removal experiment in montane Australia. Specifically we tested whether rabbits in two sites with reduced fox numbers moved further from refuge than rabbits in two sites with abundant foxes. We then compared diet quality by analysing stomach contents, gut morphology and age-specific body mass to determine if release from predation risk enables rabbits to access higher quality food and hence attain higher body mass and condition. During spotlighting on three quarterly surveys in 1994-1995, rabbits in fox removal sites were observed, on average, three times further from refuge compared to rabbits at sites with foxes. However, this freedom to forage far from cover did not translate into a higher quality diet. Analysis of the nitrogen and neutral-detergent fibre content of stomach samples taken from a shot sample of rabbits at their peak densities after fox removal showed no differences in short-term diet quality of male or female rabbits due to fox removal. In contrast, analyses of gut morphologies, which reflect long-term fibre intake, suggested that rabbits in removal sites fed on a diet higher in fibre and hence of lower quality. This was possibly due to the large increases in rabbit density associated with fox removal. Despite this, male rabbits in fox removal sites were heavier for their age, had longer intestines, and heavier stomach and gut contents. We suggest that rabbits in fox removal sites compensated for the lower quality diet by increasing intake which enabled them to maintain higher age-specific body mass but only because predation risk was reduced. This result highlights the untenable link between resource limitation and predation risk.