Over 30% of extant birds are currently threatened by invasive species (BirdLife International 2013) and half of the planet’s recent bird extinctions have been linked with invasive alien species (IAS) (BirdLife International 2008). Birds native to oceanic islands are especially vulnerable to IAS such as cats. Feral cats are opportunistic predators that can have both direct and indirect impacts on native fauna (Medina et al. 2011, Nishimura et al. 1999).

A meta-analysis of literature from across the globe demonstrates the issue of feral cats on island biodiversity. Their impacts have been reported on at least 175 species (25 reptiles, 123 birds, 27 mammals) and from at least 120 islands. Feral cats on islands have been shown to be responsible for at least 14% of global bird, mammal and reptile extinctions and are the principal threat to almost 8% of Critically Endangered birds, mammals and reptiles. Cats have been found to impact 48 taxa of endemic bird with 49% being terrestrial birds and 36% seabirds, with these numbers likely underestimates as not all islands and impacted species have been studied (Medina et al. 2011).

One way in which these impacts can be reduced is through predator eradication. A global prioritization exercise for islands requiring cat population management was conducted by Nogales and colleagues (2013). Islands were filtered for feasibility according to their size and human population size, resulting in 12 islands in which eradication would be both feasible and also urgently needed to alleviate pressures on Critically Endangered species.

Feral cat eradication programmes can however be controversial, and can be complicated by island size, human population size and the need to avoid the removal of domestic cats (Ratcliffe et al. 2009). Successful eradication of feral cats has however been conducted on 83 islands worldwide (Campbell et al. 2011), enabling the recolonization of seabird species such as those on Ascension island following a two year cat removal programme (Ratcliffe et al. 2009).