Action: Control mammalian predators on islands for parrots
Two before-and-after studies in New Zealand found reduced nest predation and successful recolonisation of an island following invasive mammal eradication or control.
The kakapo Strigops habroptila is a large, flightless parrot, once common across New Zealand but almost wiped out by the late 20th century due to predation of adults by feral cats Felis catus, dogs Canis familiaris and mustelids and the loss of eggs and chicks to rats Rattus spp. Starting in the 1970s, the remaining birds were translocated to islands free from cats and populations were very intensively managed (see ‘General responses to small and declining populations’).
The Kermadec red-crowned parakeet Cyanoramphus movazelandiae, also from New Zealand was the first parrot to recolonise an island after predator removal.
The effectiveness assessment of the control of mammalian predators on islands was carried out across all bird species groups.
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.
- Jansen W.P. (2005) Rat Rattus control at nests of the endangered kakapo Strigops habroptilus on Codfish Island, New Zealand. Conservation Evidence, 2, 1-2
- Ortiz-Catedral L., Ismar S.M.H. & Baird K. (2009) Recolonization of Raoul Island by Kermadec red-crowned parakeets Cyanoramphus novaezelandiae cyanurus after eradication of invasive predators, Kermadec Islands archipelago, New Zealand. Conservation Evidence, 6, 26-30