Control mammalian predators on islands

Overall effectiveness category Beneficial
Number of studies: 2
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How is the evidence assessed?

Effectiveness

81%
Certainty

78%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

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.

Study locations

Key messages

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.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

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.
Study and other actions tested
Referenced paper
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.
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.
Study and other actions tested
Referenced paper
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.

Please cite as:

Williams, D.R., Child, M.F., Dicks, L.V., Ockendon, N., Pople, R.G., Showler, D.A., Walsh, J.C., zu Ermgassen, E.K.H.J. & Sutherland, W.J. (2020) Bird Conservation. Pages 137-281 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Bird Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Control mammalian predators on islands Action Link	Beneficial	2	Synopsis Link
Control mammalian predators on islands for raptors Action Link	Awaiting assessment	1	Synopsis Link
Control predators not on islands for cranes Action Link	Awaiting assessment	1	Synopsis Link