Movement behaviour of a translocated female ship rat and her offspring in a low rat density New Zealand forest

Dispersal is a fundamentally important aspect of animal behaviour, but empirical data describing it are lacking for many species. Here, we report on a field study aimed at measuring post-weaning movement distances of juvenile ship rats (Rattus rattus) and their mother away from a known natal nest site in an area with low conspecific population density. The movement behaviour of invasive species at low density is of particular interest, as it can inform design of surveillance arrays to detect incursion into predator-free areas. Detecting a single invading individual requires intensive effort. An alternative approach is to focus on detecting newly-established breeding populations, while they are still spatially-restricted and able to be eliminated with timely and effective incursion response. We released a bio-marked rat mother and litter into an area recently treated with sodium fluroacetate (1080) and monitored their behaviour for 12 weeks. Final capture locations ranged up to 675 m from the release location for the juveniles, with 796 m between known siblings. The total range length for the mother exceeded 1.5 km. Although we found no evidence that the movements of the family as a collective extended further than those of the mother alone, the concept of targeting detection efforts to breeding populations warrants further investigation due to the improved probability of detecting at least one of multiple individuals, rather than a single invader.