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

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.

入侵食肉动物正威胁着阿奥特罗阿（Aotearoa）的本土动物区系（indigenous fauna），但其影响随时间、空间及物种类群的不同而存在显著差异。保护策略亟需掌握针对不同生态系统的捕食者-猎物动态（predator-prey dynamics）知识，并需纳入长期类群动态变化（guild shifts）的考量因素。为构建此类知识体系，我们基于覆盖20年（1998–2021年）、涵盖南岛多个以森林为主的山地生态系统的数据集，对啄羊鹦鹉（kea）的存活率开展建模研究——啄羊鹦鹉是一类寿命较长、地面筑巢且分布范围广泛的鹦鹉类群。研究结果显示，啄羊鹦鹉在东部生态系统中的存活率显著低于西部生态系统；在食肉动物种群爆发期间其存活率会受到抑制，而在实施捕食者防控措施后存活率则会提升。所有年龄段及雌雄个体的啄羊鹦鹉均会在觅食与夜栖过程中遭到白鼬（stoats）和野化家猫（feral cats）的捕食，而非筑巢阶段。白鼬捕食在所有调查生态系统中均有发生，而野化家猫的捕食行为则更多集中于东部生态系统。多数情境下的年存活率处于较高水平（成鸟存活率>90%，幼鸟存活率>70%），但2020–2021年东部生态系统中白鼬与野化家猫的捕食量达到峰值，导致成鸟存活率降至60%以下。此次捕食峰值紧随东部山毛榉林中食肉动物的主要猎物——啮齿动物的种群崩溃之后出现。我们据此得出结论：食肉动物对啄羊鹦鹉的影响主要集中在植物结实大年之后的年份。文末给出了相应的管理建议。