Effects of the aerial application of 1080 to control pest mammals on kea reproductive success

The kea (Nestor notabilis) and other New Zealand forest birds are threatened by predation by introduced mammals. Mammal control for biodiversity conservation in New Zealand commonly involves the aerial application of cereal-pellet baits containing sodium fluoroacetate ('Compound 1080'), but its effectiveness for kea conservation has not previously been assessed. This study examined the effects of aerial 1080 on the reproductive success of kea in a lowland rimu forest on the West Coast of New Zealand's South Island. We measured three parameters which collectively describe annual reproductive success (nesting frequency, nest survival and final chick count), within a Before-After-Control-Impact experiment. The Impact site was a 30 000 ha area over which 1080 baits were aerially applied in the spring of a rimu (Dacrydium cupressinum) mast year (i.e. with heavy seedfall), with the After phase of the experiment lasting for two kea nesting seasons. The invasive mammals ship rat (Rattus rattus), house mouse (Mus musculus), brushtail possum (Trichosurus vulpecula) and stoat (Mustela erminea), which are potential predators of kea nests, were much less abundant in the Impact site after 1080 application, on the basis of standard indexing techniques. There was strong statistical support for an effect of aerial 1080 on kea nest survival. Aerial 1080 improved the odds of daily nest survival by a factor of 9.1 at the treatment site. Nest survival rates in the Control and Impact sites, before the application of 1080, were 21% and 46.4%, respectively. After the application of 1080 to the Impact site, nest survival increased to 84.8% in this site, whereas it declined to 12.2% in the untreated Control site. This substantial positive effect of aerial 1080 on kea nest survival is attributed to the effective control of mammalian nest predators, particularly the secondary poisoning of stoats.