Action: Control mammalian predators on islands
The assessment of the effectiveness of this intervention was based on a total of 33 studies across all species groups. See Background section below for links to the evidence for the control of mammalian predators on islands on specific species groups.
A paired sites study from Finland and a literature review from the UK found increased bird species richness and abundance or population recoveries and recolonisations, following the control or eradication of mammalian predators.
- Predators removed included American mink Mustela vison, rats Rattus spp. pigs Sus scrofa, cats Felis catus, dogs Canis familiaris and grey fox Dusicyon griseus.
Humans have introduced mammalian predators to hundreds of islands across the world, most frequently rats Rattus spp., mice Mus spp. and cats Felis cattus, but many others as well. These have had a devastating impact on bird populations on islands, with the historic probability of extinction on islands being well correlated with the number of introduced mammal species (Blackburn et al. 2004).
Most control efforts for rodents are through poisoning (with a 2007 review suggesting that bait stations are more effective than broadcast baiting, Howald et al. 2007), whilst trapping and hunting appear to be more effective for cats (Nogales et al. 2004) and larger mammals. However, this synopsis only discusses the impacts of eradication or control on native bird populations, not the details of eradication programmes themselves. The effects of different control methods will be discussed in detail in a forthcoming Conservation Evidence synopsis on invasive species.
Below are two studies describing the impacts of island predator removal on bird communities. Studies describing the effects on gamebirds, parrots, pigeons, rails, raptors, seabirds, songbirds, waders and wildfowl are also available.
Blackburn, T.M., Cassey, P., Duncan, R.P., Evans, K.L. & Gaston, K.J. (2004) Avian extinction and mammalian introductions on oceanic islands. Science, 305, 1955–1958.
Howald, G., Donlan, C., Galván, J.P., Russell, J.C., Parkes, J., Samaniego, A., Wang, Y., Veitch, D., Genovesi, P., Pascal, M., Saunders, A. & Tershy, B. (2007) Invasive rodent eradication on islands. Conservation Biology, 21, 1258–1268.
Nogales, M., Martín, A., Tershy, B.R., Donlan, C.J., Veitch, D., Puerta, N., Wood, B. & Alonso, J. (2004) A review of feral cat eradication on islands. Conservation Biology, 18, 310–319.
Supporting evidence from individual studies
A paired sites before-and-after study on four paired study areas (72-139 km2) of >60 small islands in Archipelago National Park, southwest Finland (Nordstrom & Korpimaki 2004) found that, following the removal of up to 63 introduced and predatory American mink Mustela vison each year in 1992-3 and 1998, experimental areas had significantly higher species richness and abundance, compared to control areas. There was a significant positive relationship between the degree of isolation of the islands and species richness and abundance in control, but not experimental areas. In all areas, larger islands had more pairs and more species.
A 2010 literature review (Hilton & Cuthbert 2010) found that all five successful invasive mammal eradication and control programmes on United Kingdom Overseas Territories found native bird population recoveries and/or recolonisations following the programmes. Recovering species included seabirds and songbirds. The impacts of ten more eradication programmes have not been recorded or published, whilst a final eradication attempt (in the British Indian Ocean Territories) failed to remove black rats Rattus rattus. Eradicated/controlled species included pigs Sus scrofa, cats Felis catus, rats Rattus spp., dogs Canis familiaris and grey fox Dusicyon griseus.
- Nordström M. & Korpimäki E. (2004) Effects of island isolation and feral mink removal on bird communities on small islands in the Baltic Sea. Journal of Animal Ecology, 783, 424-433
- Hilton G.M. & Cuthbert R.J. (2010) The catastrophic impact of invasive mammalian predators on birds of the UK Overseas Territories: a review and synthesis. Ibis, 152, 443-458