Recolonisation of rabbit warrens following coordinated ripping programs in Victoria, south-eastern Australia

Context. Warren ripping has been demonstrated to be an effective tool for controlling rabbit populations. However, few studies have examined factors influencing the rate at which ripped warrens are likely to be recolonised (i.e. be re-opened). Aims. To examine factors influencing the recolonisation of ripped warrens by rabbits by using data collected on 555 warrens for up to 15 years following coordinated ripping programs at 12 sites in Victoria, south-eastern Australia. Methods. Warren-monitoring data (number of active and inactive warren entrances) were analysed using discrete-time survival analysis to determine the effects of warren-level and site-level covariates on the recolonisation of ripped warrens. Key results. Warren recolonisation was related to the distance between the ripped warren and the nearest active warren, the number of active entrances in the nearest warren, the initial number of active entrances in the ripped warren and the rabbit spotlight abundance index at the site. The probability of warren recolonisation was highest for ripped warrens within 1 km of an active warren and negligible beyond 3 km. The probability of warren recolonisation also increased by 22% for every increase in the rabbit spotlight count at the site by 10 rabbits km(-1). Conclusions. The recolonisation of ripped warrens was highly influenced by both the distance to, and size of, neighbouring active warrens. Larger warrens also appear to be preferentially recolonised compared with smaller warrens, suggesting that recolonisation of ripped areas may be related to habitat quality. The present results are consistent with ideas from classical metapopulation theory predicting that the rates of colonisation of vacant patches are dependent on both the proximity and size of the source population as well as the quality of habitat patches. Implications. Although coordinated warren ripping programs are effective at achieving long-term control of rabbits, their efficiency at maintaining low rabbit populations can be increased by adopting an adaptive monitoring program that incorporates warren size and the spatial relationships among warrens, and using this information to better target maintenance-control activities.