Spatial distribution of probable ship rat reinvaders in a pest-fenced ecosanctuary

Managers of ecosanctuaries often need to make decisions in the face of uncertainty. Model-based tools which aim to assist this process, for example proof-of-absence models, are underpinned by assumptions about the behaviour of target animals, including their spatial movements. In some cases, however, there are few empirical data to draw on to inform these models. The movement behaviour of individual pests in low-density environments, as well as the dispersal of juveniles away from their natal location, is poorly understood for many species, including the ship rat (Rattus rattus). We document probable ship rat incursions and a breeding event within a pest-fenced ecosanctuary in Nelson, New Zealand. A comparison of genetic profiles suggested breeding had taken place, with 13 of 18 rats captured likely to be a family group (mother and likely three litters of offspring). Straight line distances from the recovery location of the putative mother to those of her probable offspring ranged up to a maximum of 1510 m, but were mostly within 200 m. No significant effect of sex, weight or head-body length on movement distance was found. Rat captures and detections appeared to be concentrated around waterways. The presence of unrelated rats in the capture sample points to eradication survivors, several separate incursion events, or a combination of both. Contributions of new data, such as this, help ecosanctuary managers by guiding better design of efficient pest detection networks, and improve models that aid their decision-making.