Assessing habitat suitability for karure | kakaruia | Chatham Island black robin (Petroica traversi): Integrating invertebrate surveys, DNA metabarcoding, and foraging ecology

Abstract

The karure | kakaruia | Chatham Island black robin (Petroica traversi) is one of New Zealand's most remarkable conservation achievements, recovering from a mere five birds in 1980 to around 330 today. However, the species remains Nationally Critical and restricted to two small islands, making establishment of additional populations essential for long-term prosperity. A previous translocation attempt to Rangiauria | Rangiaotea |Pitt Island failed, with inadequate food resources hypothesised as a contributing factor, yet black robin dietary requirements and prey availability at potential translocation sites remain poorly understood. This study integrated invertebrate community surveys, DNA metabarcoding of faecal samples, and behavioural observations to characterise black robin diet, foraging behaviour and food availability, aiming to assess habitat suitability across the Chatham Islands. In Chapter Two I examined invertebrate communities across four forested sites across the Chatham Island archipelago; the currently inhabited Woolshed Bush and Top Bush on Hokorereoro | Rangatira | Southeast Island, previously failed translocation site Elizabeth Ellen Preece Conservation Covenant | Caravan Bush on Rangiauria | Rangiaotea | Pitt Island, and potential future translocation site Chudleigh Conservation Area on Rēkohu | Wharekauri | Chatham Island. Analyses revealed that predator free sites (Woolshed Bush and Top Bush) supported significantly higher ground-active invertebrate biomass. This difference was driven by large-bodied cave wētā and ground beetles, which were abundant on Rangatira Island but absent from Caravan Bush and Chudleigh Conservation Area. Surprisingly, Woolshed Bush and Top Bush showed similar invertebrate communities despite different black robin densities, indicating that prey availability alone does not determine habitat quality. DNA metabarcoding of faecal samples in Chapter Three revealed that black robin are generalist insectivores, with Coleoptera, Diptera, and Orthoptera comprising the majority of their diet. Dietary composition showed no significant differences between sites, indicating consistent resource use across Woolshed Bush and Top Bush. Foraging observations confirmed strong ground-level preferences, with 82.2% of foraging events occurring at ground level, emphasising the importance of intact forest floor environments for future translocation sites. This research demonstrates that black robin persistence depends on multiple interacting factors. Future translocation sites should include abundant large-bodied prey, intact forest floors with deep leaf litter supporting ground foraging, effective predator control or predator-free status, and mature forest structure. DNA metabarcoding proved essential for revealing dietary composition that would be impossible to detect through observation alone by characterising consumption of cryptic prey taxa. While food availability is necessary for translocation success, it is not a sole determining factor; other habitat features such as nest site availability and predator presence must also be considered. The methods I have established here provide a repeatable framework for evidence-based translocation planning.