The biology and conservation of the Fijian crested iguana Brachylophus vitiensis

The Fijian crested iguana, Brachylophus vitiensis, is an iconic animal for conservation in the South Pacific. Its striking appearance, Critically Endangered listing and disjunct range compared to other iguanids render it of particular interest to both conservation biologists and biogeographers. Yet data on the biology and ecology of crested iguanas in their tropical dry forest habitat remains scant. In Fiji, both tropical dry forests and the endemic crested iguanas are threatened on a national level by anthropogenic factors. In this thesis I shed light on reproduction and spatial ecology of the sole sustainable population of Fijian crested iguanas, on the Yadua Taba Island sanctuary with the ultimate aim of informing long-term conservation planning for this species. The previously unknown nesting ecology of B. vitiensis was examined over two field seasons on the iguana sanctuary island. Tropical dry forest ecosystems such as that found on Yadua Taba, occur throughout tropical and subtropical zones and one of their primary characteristics is that they are structurally and functionally constrained by seasonal fluctuations in rainfall. Organisms within them synchronise growth and reproduction with water availability, and many exhibit adaptations to drought conditions. Evaluation of iguana reproductive status revealed that only 52% of adult females reproduced in a given year. I suggest that female crested iguanas have adopted a biennial mode of reproduction in response to resource limitation. No evidence was found 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{u00B0}C), levels of site openness (10.9%) and total incident radiation (2.57 MJ m{u00B2} 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). The incubation period was extremely long (mean 256 days) and spanned the eight-month dry season. Mean hatching success also was high (87%). Reproductive strategy is discussed in relation to the environmental conditions of the tropical dry forest habitat on Yadua Taba. While Yadua Taba supports the only secure population of Fijian crested iguanas this population is extremely dense with estimates of over 10,000 iguanas living on the 70 ha island. In order to investigate the spatial ecology and intraspecific interactions of B. vitiensis a mark and recapture survey was conducted over two wet seasons from late 2005 to early 2007. Of the 338 study animals 73% of adults (88 males, 69 females) were observed in both wet seasons and 27% (30 male, 28 female) in only a single wet season. This species exhibits male-biased sexual size dimorphism, which has been linked in other lizard species to territoriality, aggression and larger male home ranges. The data indicate that male Fijian crested iguanas are territorial and exhibit high injury levels, which are indicative of frequent agonistic interactions. Support was not evident for larger home range size in adult males relative to adult females, however, male and female home range holders were larger than 'floater' individuals. Males with established home ranges also had larger femoral pores, for their body size, than 'floater' males. Home range areas were small in comparison to those of other iguana species and we speculate that the extreme population density impacts considerably on the spatial ecology of this population. There was extensive home range overlap within and between the sexes, however, when compared to other iguana species the overlap levels were moderate. Intersexual overlap was greater than intrasexual overlap for both sexes, and continuing male-female pairings were observed among home range holders. This research provides a broader understanding of crested iguana nesting and spatial ecology and is a step towards the successful implementation of the Species Recovery Plan for this species. Results from this research have ramifications for future conservation efforts, through the mitigation of agonistic interactions and stress in captivity, and in the maintenance of genetic diversity in small populations