Habitat-specific effectiveness of feral cat control for the conservation of an endemic ground-nesting bird species

1. Invasive non-native species are one of the greatest drivers of the loss of biodiversity world-wide. Consequently, removing or controlling invasive predators should generally benefit vulnerable native species. However, especially on islands, where most mammalian predators are introduced, these predators may also prey on other invasive mammals. Removing only apex predators may lead to increases of meso-predators that may in turn increase predation pressure on native wildlife. 2. We examined the benefits of a feral cat Felis catus control programme on nest survival of a critically endangered ground-nesting bird, the St Helena Plover Charadrius sanctaehelenae in two habitat types, harbouring c. 30% of the global population of this species. We monitored nest success and the activity of introduced mammals (cats, rabbits Oryctolagus cuniculus, rats Rattus rattus and Rattus norvegicus, and mice Mus musculus) over 2 years, before and after controlling feral cats. 3. Live trapping removed 56 feral cats from our study areas. In the semi-desert, rabbit and mouse activity increased, but rat activity remained low after feral cat control. In pastures, rat and mouse activity increased after feral cat control, while rabbit activity remained constant. 4. Nest survival of plovers increased more than threefold in the semi-desert, but increased only marginally in pastures. This difference may be due to an increase in rat activity and potentially rat predation following cat control in pastures, whereas no increase in rat activity was observed in the semi-desert. 5. Synthesis and applications. Our study shows habitat-specific consequences of feral cat control on ground-nesting bird productivity after 1 year, probably mediated by differences in the availability of alternative prey. The results highlight the importance of experimental trials and a thorough understanding of the interactions between multiple invasive species before predator-control operations are implemented over larger scales. On islands with multiple invasive species, there may not be a simple generic approach to predator management (other than removing all invasive species simultaneously).