Nesting ecology of the critically endangered Fijian Crested Iguana Brachylophus vitiensis in a Pacific tropical dry forest

Abstract

Tropical dry forest (TDF) ecosystems occur throughout tropical and subtropical zones and one of their primary characteristics is that they are structurally and functionally constrained by seasonal fluctuations in moisture levels. Organisms within them synchronize growth and reproduction with water availability and many exhibit adaptations to drought conditions. We examined the previously unknown nesting ecology of the Critically Endangered Fijian Crested Iguana Brachylophus vitiensis a TDF specialist, on the Fijian island of Yadua Taba over two field seasons. In Fiji, the TDF and the endemic Crested Iguanas are threatened on a national level by anthropogenic factors and Yadua Taba Island remains the only protected site. Evaluation of adult female reproductive status revealed that only 52% of adult females reproduced in a given year. We suggest that female Crested Iguanas have adopted a biennial mode of reproduction in response to resource limitation.We found no evidence for communal nesting or nest site defence by females. All nest burrows were constructed on the forest floor in shaded areas. Mean nest temperatures (24.5°C), levels of site openness (10.9%) and total incident radiation (2.57 MJ m2 day) recorded at nest sites were less than those reported for other Iguaninae. Mean egg size (17.9 g) was large relative to most Iguaninae and was independent of the small mean clutch size (2.9 eggs). Mean incubation period was extremely long (256 days) and spanned the eight-month dry season. Mean hatching success also was high (87%). We examine reproductive strategy in relation to the environmental conditions of the TDF habitat on Yadua Taba. This research provides a broader understanding of Crested Iguana nesting ecology and is a step towards the successful implementation of the Species Recovery Plan for this species.