A test of whether rabbit abundance increases following predator control in a rural landscape

Abstract

Context In New Zealand and Australia, rural landowners believe that local control of invasive predators aimed at protecting the indigenous biota exacerbates European rabbit (Oryctolagus cuniculus) problems on their land. Aims We tested this using rabbit index data collected in replicated areas with and without predator control in rural landscapes of the Hawke’s Bay region of New Zealand. Methods Spotlight data were available from two ecological restoration areas. For the Cape to City area, data were collected from 2016 to 2021, with three sites subjected to ongoing predator control (traps deployed in 2016 and 2017) and two sites untreated. For the Poutiri Ao ō Tāne area, data were collected from 2012 to 2021, with two sites subjected to ongoing predator control (beginning in 2012) and three sites untreated. Generalised linear mixed-effects models were used to assess whether predator control was a statistically significant predictor of rabbit counts. Cameras were also deployed annually, beginning in 2015, in the treatment and non-treatment areas in Cape to City. Mixed-effects models were fitted to the camera detection data using a ‘Before After Control Impact’ framework to assess whether camera detection rates of rabbits changed with predator control. Key results Contrary to landowner expectations, fewer rabbits were counted under spotlight at the predator control sites at Cape to City, although no effect was detected in the camera detection data. More rabbits were counted on the predator control sites at Poutiri Ao ō Tāne, but this effect was not statistically significant and only became apparent in the last 2 years of the 9-year monitoring period. Conclusions The effects of predator control on rabbit abundance indices in the Hawke’s Bay region were contradictory and inconclusive. This suggests that the influence of predators on rabbit populations is minor compared with other sources of population limitation or regulation, such as disease and poor food quality. Implications The absence of a definitive predator effect should reassure landowners concerned about potential rabbit population outbreaks following predator control.