Abstract
Effective conservation management relies on understanding the ecological factors behind population decline. Tracking movement patterns, quantifying survival, and understanding demographics such as age and sex structure can provide vital context for threatened wildlife recovery plans. Introduced mammalian predators remain a major threat to birds in Aotearoa New Zealand. Formerly widespread, the pukunui (Anarhynchus obscurus obscurus) is an endemic plover that now exists as a relict population of ~100 birds primarily due to feral cat predation, and is threat-listed as “Nationally Critical”. Despite active cat control at their known breeding grounds on the mountaintops of Rakiura/Stewart Island, pukunui have declined by 64% since 2009. Furthermore, where 60 to 80% of the population go during the breeding season is unresolved. Intersexual variation in pukunui is also poorly understood, and putative sexual dimorphism has not been quantified. Uncertainty around these factors limit the potential of current management techniques.
My overarching aim was to provide insight into where the ‘missing’ pukunui nest by tracking individuals through the breeding season. Device malfunction and low capture rates limited tracking data from adults, shifting focus to include juveniles which also frequently visit breeding grounds. Over two years, 12 pukunui (50% adults; 75% males) were tagged at three winter flocking sites. The longest tracking period lasted 388 days, and tracking periods averaged 62 days per individual. Data revealed wide-ranging movements across Rakiura, and five potential breeding sites not known from traditional survey methods. One pukunui nested during tracking, and its movement patterns reflected different stages of the nesting cycle. In line with previous speculation, this male consistently incubated at night regardless of tide and only foraged at low tide in daylight, highlighting the potential for tracking data to indicate previously unknown nesting grounds to prioritise for monitoring and predator control.
In the hope of establishing a reliable field-sexing technique, I evaluated the morphological variation between genetically sexed male and female pukunui. Morphometric measurements (body mass, head, bill and tarsus length) were tested for sexual dimorphism, but high overlap rendered them unreliable for predicting sex. Photo evaluation revealed consistent intersexual differences in pukunui breeding plumage traits, with females appearing duller and more mottled with streaked flanks. A photo identification quiz completed by 87 participants showed high agreement with my predictions of unknown sex birds and an overall accuracy of 87%, indicating pukunui can be sexed visually even with limited experience. Incorporating plumage-based predictions improved sex determination from 83% to 95%, confirming a female-biased sex ratio. I also investigated intersexual differences in annual survival through a Cormack-Jolly-Seber analysis. Survival modelling revealed an average of 15% lower survival in male pukunui over the last five years, consistent with nocturnal incubation habits and elevated predation risk.
Together, my findings provide critical information to support pukunui conservation, including the detection of potential breeding sites, sex-specific survival patterns, evidence of male-biased mortality, and an effective field-based sexing technique. By integrating these results with current management strategies, I hope to augment the recovery prospects of this critically endangered shorebird.