Localised control of an introduced predator: creating problems for the future?

Introduced mammalian predators have had significant impacts on many native prey species. Although control of such predators for conservation management is becoming increasingly commonplace, it is often undertaken at a relatively small scale in relation to the overall predator population. Processes such as immigration mean that it remains difficult to determine the effectiveness of control measures. We investigated the impacts of feral ferret Mustela furo removal on the entire feral ferret population on Rathlin Island, UK. Removal of ferrets prior to breeding led to a substantial increase in the post-dispersal population through the enhanced survival of juveniles. Despite increased numbers, overwinter survival remained high, potentially aided by the reduced territoriality shown by this feral species compared to wild carnivores. The response of this ferret population to control is a further illustration of the complex ecological processes and outcomes arising from the anthropogenic disruption of wildlife populations. It highlights how partial or localised management may prove ineffective, and at worst might exacerbate the problems that management was designed to avert.