Conservation Evidence strives to be as useful to conservationists as possible. Please take our survey to help the team improve our resource.

Providing evidence to improve practice

Action: Control mammalian predators on islands for parrots Bird Conservation

Key messages

Read our guidance on Key messages before continuing

Two before-and-after studies in New Zealand found reduced nest predation and successful recolonisation of an island following invasive mammal eradication or control.


Supporting evidence from individual studies


A small before-and-after study on Codfish Island (1,500 ha), New Zealand (Jansen 2005) found that none of six kakapo Strigops habroptilus nests were lost to rats Rattus spp. in 1997, when there was intensive trapping and poisoning of rats close to nests (in conjunction with remotely operated detonators to scare rats, see ‘Guard nests to prevent predation’). In contrast, there were potentially unsustainable predation rates before 1997.  The study does not adequately describe the impact of predator control on the species – the translocations and subsequent population stabilisation would only have been possible with prior control.



A before-and-after study on Raoul Island (2,938 ha), Kermadec Islands, New Zealand (Ortiz-Catedral et al. 2009) found that the island was recolonised by Kermadec red-crowned parakeets Cyanoramphus movazelandiae in 2008, following the eradication of goats Capra hircus by hunting (in 1986) and cats Felis cattus, brown rats Rattus norvegicus and black rats R. rattus by poisoning and hunting (between 2002 and 2004). In 2008 the parakeet population was at least 100 individuals, of which 44 were born in 2008. Before this, parakeets had been absent for 172 years.


Referenced papers

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. (2019) Bird Conservation. Pages 141-290 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2019. Open Book Publishers, Cambridge, UK.