Sounding out the nest: Unobtrusive localisation of North Island brown kiwi (Apteryx mantelli) incubation burrows

Monitoring breeding outcomes of cryptic nocturnal species such as the North Island brown kiwi (Apteryx mantelli) is an important aim for conservation management in New Zealand. While fitting male kiwi with radio transmitters enables incubation burrows to be found and monitored, it is invasive and expensive. Remote monitoring methods (without handling of birds) are preferable. Here we investigate the extent to which it is practical to find North Island brown kiwi incubation burrows based on remote monitoring, motivated by anecdotal reports that incubating males call close to their incubation burrow on first emergence. We test this observation, and then use it to demonstrate how a combination of acoustic recorders, human listening, and trail cameras can be deployed to locate the burrow with minimal disturbance, based on the male’s first call of the night. Our analysis of an incubating brown kiwi male’s first call in the evening as a function of distance from the burrow shows that for more than half the time monitored he called within 10 minutes of leaving his burrow and that on these nights, he was usually less than 35 m from it. Along with backtracking of kiwi footsteps, this enables the localisation of the burrow. We outline a workflow for the method based on our experience and discuss how it can be made more efficient and usable in the future. Our method facilitates the finding of nests, and hence of chicks, without the need for adult kiwi to be fitted with transmitters.