Irruptive dynamics of invasive carnivores and prey populations, and predator control, affect kea survivorship across the Southern Alps

Abstract

ABSTRACT Invasive carnivores are threatening the indigenous fauna of Aotearoa, but impacts vary with time, space and species. Conservation strategies require knowledge of predator-prey dynamics specific to different ecosystems and allowing for long-term guild shifts. To build this knowledge, we model the survivorship of the kea, a long-lived, ground-nesting parrot with an expansive species-range, using a dataset spanning two decades (1998–2021) and spanning several forest-dominated South Island montane ecosystems. Kea survivorship was lower in eastern ecosystems compared to western ones, depressed during carnivore irruptions, and elevated after predator control. Kea of all ages and both sexes fell prey to stoats and feral cats whilst foraging and roosting, not whilst nesting. Stoat depredation happened in all ecosystems, whereas feral cats featured more in eastern ones. Annual survivorship was high in most contexts (adults > 90%, juveniles > 70%), but a peak in stoat and feral cat predation in eastern ecosystems during 2020–2021 reduced adult survival to <60%. This predation peak followed a rodent population crash, the primary prey of carnivores in eastern beech forests. We conclude that predator impacts on kea are concentrated into post-mast years. Recommendations for management are provided.