lntraspecific variation in the foraging ecology and morphology of kea Nestor notabilis
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Intraspecific variation can have knock-on ecological consequences on resource use, morphology and population dynamics. Kea parrots, Nestor notabilis, have a number of attributes that suggest that intraspecific variation in their foraging ecology may exist: their bill is sexually dimorphic, they inhabit two very different environments (montane and temperate rainforest), and they have a protracted juvenile period during which time they may learn to exploit their environment more effectively, suggesting foraging differences among age classes. In this thesis, I investigated intraspecific variation in the foraging ecology of kea, and its link with variation in morphological traits. Firstly, I conducted field observations and faecal sample analyses and found that kea in the rainforest habitat ate invertebrates three times as frequently as those in the high-altitude habitat and that adult males ate more roots and invertebrates than immature kea. I then established kea-specific diet-tissue discrimination factors for carbon and nitrogen stable isotope ratios and regression equations to convert between the stable carbon and nitrogen isotope ratios of kea blood and feather samples. I subsequently used stable isotope mixing models, based on these kea-specific values, to establish the contribution of plant and animal matter to the kea’s diet. I confirmed that the diet of kea in the rainforest habitat is mainly animal-based, whereas the diet of kea in high altitude habitat is mainly plant-based, and also found that, in the rainforest, males ate more animal matter than females. Additionally, I found that birds sampled in the rainforest had longer bills and heads than those in high-altitude regions, which suggests a link between kea bill and head length and foraging ecology. I then measured the strength of the relationship between bill/head length and the consumption of animal matter. I found a larger effect size than has been recorded between diet and morphology in other species, which demonstrated that this relationship is strong enough that changes in the degree to which kea rely on invertebrate foraging could result in changes in their morphology. Finally, I examined differences in the kea’s isotopic niche and found the first evidence for niche partitioning among male and female kea in high-altitude habitat. This work has demonstrated that there is considerable intraspecific variation within the foraging ecology and behaviour of kea and that this variation is linked with differences in morphology among the sexes and among different populations.