Colour variation and behaviour of the cryptic New Zealand frog Leiopelma archeyi

Understanding the ecology of cryptic species is essential for designing effective monitoring and conservation strategies. Leiopelma archeyi is a native New Zealand frog with cryptic colouration, patterning, and behaviour. Our study examined dorsal colour variation and climbing behaviour in this species. Our first aim was to investigate if L. archeyi demonstrates colour crypsis by background-matching. Secondly, we determined if green pigmentation is lost as frogs age by comparing frog body size (a proxy for age) with the percentage of green on their dorsal surface. Finally, to better understand frog climbing behaviour, we examined which factors influenced the height above ground that frogs were found at. The study was conducted in Wharekirauponga New Zealand between 2017 and 2021. Visual nocturnal surveys were undertaken in 112 survey plots where frogs were captured, photographed, and measured. Unexpectedly, L. archeyi tended to not show background-matching between their substrate and the colour of their dorsum. Among other possible explanations, this trend might suggest their disruptive colouring is enough to camouflage them in their visually complex habitat, or the trend might be related to observer bias. Larger L. archeyi individuals had less green on their dorsal surface compared to smaller ones suggesting colour change with increasing age does occur in L. archeyi. This could reduce the longer-term reliability of photographs to identify individuals. Larger L. archeyi were also found at greater heights off the ground compared to smaller individuals, a pattern which, among other possible reasons, could be due to reduced biological constraints (e.g. risk of predation or desiccation) for larger frogs. Finally, L. archeyi climbed to greater heights off the ground at cooler temperatures and climbing behaviour was uncommon in the summer months. Improving our understanding of L. archeyi’s behaviour and ecology is an essential component of successfully conserving this endangered species.