Rodent predation and specialised avian habitat requirements drive extinction risk for endemic island songbirds in the south-west Pacific

Abstract

Island endemic birds represent approximately 90% of contemporary avian extinctions globally. Introduced predators and land-use change are key drivers of population decline in this group. Where multiple threats may compound the impacts on species, the implementation of complementary approaches to threat assessment can be especially valuable. Using Norfolk Island (NI) in the south-west Pacific as an exemplar, we assessed daily nest survival rates for five endemic songbirds (NI Robin Petroica multicolor, NI Gerygone Gerygone modesta, Slender-billed White-eye Zosterops tenuirostris, NI Whistler Pachycephala pectoralis xanthoprocta and NI Fantail Rhipidura albiscapa pelzelni), monitoring 135 nests over four breeding seasons. To understand the factors associated with suitable breeding habitat, we also conducted ecological niche modelling in Maxent for all species. Depredation was the primary driver of nest failure across all species (80% of failed nests), with invasive rats (Rattus sp.) being the most common predator (61% of depredated nests) and a key predictor of nest survival. Gerygones and Fantails exhibited the highest nest survival and were also categorised as habitat generalists using ecological niche modelling. Conversely, the three species that exhibited lower nest survival (Robin, White-eye and Whistler) had specialised habitat requirements, highlighting the potential for cumulative impacts. Our data suggest that invasive rodent control within intact forested sites is a critical management action for this system, followed by strategic habitat restoration and increased connectivity. Our study provides essential ecological information for five poorly understood island songbirds and identifies key management strategies for a regional avian hotspot.