Measuring individual variation in kiwi using stereo cameras: A promising new method

Abstract

Kiwis have high conservation needs and populations are often closely monitored. Mark-recapture approaches provide useful information, but it is difficult to implement with these species. We developed a method using trail cameras that, with development, could identify individuals in the wild and may allow for a mark-recapture approach. We measured kiwi bills with high accuracy, in ideal conditions (daylight, stationary, taxidermied kiwi), using a home-modified stereo camera. Under these conditions, the level of accuracy obtained was within the required inter-observer error (<1.5%) for hand measurement of live birds. Measuring a live kiwi bill at night in field conditions imposed additional challenges. Background composition was key in correctly identifying the bill tip. Camera orientation changes (e.g., a higher, angled-down placement) may potentially mitigate at least one source of error (the correct identification of the bill tip). We were able to synchronise videos, but synchronising photos would allow for higher-quality images, providing greater accuracy in identifying features for measurements. Given ongoing improvements in trail camera technology, there is great potential to use stereo cameras for the measurement of kiwi bills to determine age class and eventually individual identification.