The ecology and anatomy of scent in the critically endangered kakapo (Strigops habroptilus) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Zoology at Massey University, Auckland, New Zealand
The focus of the research presented here is the analysis of feather scent emitted by a parrot, the kakapo (Strigops habroptilus) and the kakapo’s ability to perceive scent by studying the anatomy of its brain and the olfactory bulb. In addition, behavioural research was conducted to determine the capability of the kakapo’s closest relatives, the kea (Nestor notabilis) and kaka (N. meridionalis) to detect scents and to distinguish between different concentrations of scents.The strong odour of the kakapo is one of the many unique characteristics of this critically endan-gered parrot, but its sense of smell has never been described in detail. The kakapo is the largest par-rot worldwide, it is nocturnal and flightless. Kakapo are herbivorous and it is the only parrot with a lek breeding system. Males defend several display arenas during the breeding season and continuously produce low frequency booming calls. Females come from afar and appraise different males and choose one with which they want to mate. As in all lek mating systems some males make major contributions to the gene-pool of the next generation while others make little or no contribution. Currently it is not known what the female’s choice is based on and why some male kakapo are ‘favoured’ over others. However, it has been observed that favoured males appear to emit a stronger odour than less attractive ones (pers. comm. Kakapo Recovery Team). This study is the first to compare the chemical composition of the kakapo’s scent in relation to season, age and sex. It is also the first study to uncover the kakapo’s ability to smell by conducting a comparative examination of the anatomy and histology of the brain and the olfactory bulb. In spite of its endangered status, the kakapo is a good model in which to study olfaction, as the birds are closely monitored by the Department of Conservation, New Zealand. The birds undergo regular health checks and transmitter changes, allowing access to a large proportion of the population at once and for which their individual history is known. The study of olfaction in kakapo is important as it can contribute to the growing field of avian olfaction, and by elucidating the kakapo’s potential for olfaction conservation managers will be able to make better decisions in their attempt to save this species. The research approach adopted in this dissertation includes the analysis of feather samples from individuals of different sex and age as well as from different seasons using gas chromatography-mass spectrometry. The opportunity to examine the brain as well as the eyes of a kakapo that died at Auckland Zoo, Auckland, New Zealand, allowed a comparative study of the brain, the olfactory bulb and the visual centres (of both the thalomofulgal and the tectogucal pathways) with other Australasian parrots. Additionally, behavioural experiments with kea and kaka, the closest relativesof the kakapo, give insight into two of New Zealand endemic parrot’s and their ability to distinguish between different scents and scents of different concentrations.
The findings from this research provide evidence that kakapo distinguish themselves by having one of the largest olfactory bulbs measured in parrots and the highest number of mitral cells, responsible for the transmission of an olfactory neural signal into a behavioural response, counted in any species to date. They also have a strong odour, whose chemical composition shows sexual, age-dependent and seasonal distinction. Furthermore, the study found that kea and kaka are both able to distinguish between different scents and different concentrations of scents.The main conclusions drawn from this study are that kakapo appear to be equipped with a functional olfactory bulb, able to sense olfactory information, but also communicate information that is likely to be of social importance using their plumage scent. In conclusion, this dissertation provides the foundation for future research, in particular to examine the role of the scent in the social life in kakapo, and it provides fundamental insight into the olfactory and visual sensory abilities of the New Zealand endemic kakapo.