Gautschi, DanielStojanovic, DejanOrtiz-Catedral, LuisWilson, MelindaOlsen, PennyMacgregor, Nicholas A.Doerr, Erik D.Neaves, Linda E.Crates, RossBrown, Sarah M.Heinsohn, Robert2026-07-032026-07-030158-4197ORCID:/0000-0002-7660-309X/work/219173138ORCID:/0000-0002-1176-3244/work/219178409ORCID:/0000-0002-2514-9448/work/219179940https://hdl.handle.net/1885/733812790Invasive predators present a major threat to the conservation of native species. For birds, this often comes in the form of increased nest predation. Conservation managers have used numerous interventions to reduce this risk. However, their effectiveness varies depending on the specific technique used and the predators targeted. In this study, we tested the effectiveness of nest site modifications used to protect endangered Norfolk Island Green Parrot Cyanoramphus cookii nests from introduced mammalian predators. We compared the breeding outcomes and nest site characteristics of a sample of natural, unprotected nests with those of predator-proofed nests, and examined contemporary phenology and breeding parameters. We observed moderate, but variable, breeding seasonality, and significantly fewer nesting attempts in recent years. Nests had a median clutch size of five (range = 1–10) and a median brood size of three (range = 1–7). Nest success was 74.8% (157/210) for predator-proofed nesting attempts, and 40% (4/10) for unprotected nesting attempts. Predator-proofing had a small but significant effect on daily survival rate (estimated at 0.995 for predator-proofed nests and 0.972 for unprotected nests), but did not significantly affect the number of birds fledged. We observed nest predation by both Black Rats and feral Cats at unprotected nests. Unprotected nest sites had significantly shorter chambers than predator-proofed nest sites, suggesting that while predator-proofing significantly increases nest success for Green Parrots, preferred nest site characteristics have not been preserved through modifications. These findings highlight the importance of assessing the effectiveness of management actions regularly to inform evidence-based decision-making and adaptive management.This study was funded by the Department of Climate Change, Energy, the Environment and Water through the National Environmental Science Program, the Director of National Parks, the Ecological Society of Australia through the Holsworth Wildlife Research Endowment, and a Fenner School of Environment and Society PhD Scholarship. Fieldwork was performed under Australian National University Animal Ethics Committee approval [A2020_13] and a permit to conduct scientific research in a Commonwealth reserve or was conducted as part of ongoing management and monitoring by Norfolk Island National Park under the Norfolk Island National Park and Norfolk Island Botanic Garden Management Plan [Director of National Parks 2008–2018, 2020]. The Norfolk Island National Park (NINP) team collected the long-term monitoring data used for this study. Data from 2013 to 2018 were also collected by Luis Ortiz-Catedral, Amy Waldmann, Emma Wells, Michael Skirrow, Serena Simmonds and Nat Herewini with support from Massey University, World Parrot Trust, Auckland Zoo Conservation Fund, Disney Conservation Fund and Mohamed bin Zayed Species Conservation Fund. Lilli-Unna King provided fieldwork support for the project. Thanks to all Norfolk Island National Park staff, particularly Nigel Greenup, Joel Christian and Kenny Christian for their contributions to this project. We also thank the Norfolk Island community members who supported this project, and landholders who permitted access to their properties. We acknowledge the unique culture and identity of Norfolk Islanders, particularly the descendants of the first Pitcairn settlers, and their ongoing connection to the island where this research took place.11enPublisher Copyright: © 2025 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.Breeding parametersbreeding successintroduced predatorsinvasive speciesnest protectionpredator exclusion202510.1080/01584197.2025.2542150105012527870