Foraging ecology of kea
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Globally, bird numbers are declining, with potentially serious flow-on effects on ecosystem processes, such as seed dispersal mutualisms. However, management to maintain seed dispersal may be inappropriate if unexpected animals are the most important dispersers. Numbers of the world‘s only alpine parrot, the New Zealand kea (Nestor notabilis), have declined drastically over the last 120 years after an intense period of official persecution. Today <5000 kea remain in the wild. Previously it has been assumed that like other parrots, kea would destroy most of the seeds they eat, thereby contributing little to seed dispersal. The New Zealand alpine flora is rich in fleshy-fruited species yet has a limited disperser fauna. Consequently, we investigated the relevance of kea as a seed disperser in New Zealand‘s alpine ecosystems. Field-based foraging observations coupled with faecal analyses showed kea were by far the most important extant alpine avian frugivore. Kea selected more fruiting species (21 vs. 17 species), consumed more fruit, and dispersed more seeds (8137 vs. 795) than all other birds combined. Rates of seed predation by kea were extremely low, and evident in only 25% of species eaten. Kea are the only species that make frequent long-distance flights within and between mountain ranges. Hence, much of the effective long-distance dispersal of the alpine flora may be currently performed by kea. Conservation of kea is therefore important both for ensuring the survival of the species and for their role in seed-dispersal mutualisms for which there are few extant substitutes.
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Intraspecific variation can have knock-on ecological consequences on resource use, morphology and population dynamics. Kea have a number of attributes which suggest that intraspecific variation in their foraging ecology may exist: their bill is sexually dimorphic, they inhabit two very different environments (alpine 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. Our work demonstrates 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.
We investigated intraspecific variation in the foraging ecology of kea, and its link with variation in morphological traits. Field observations and faecal sample analyses show that kea in the rainforest habitat eat invertebrates three times as frequently as those in the alpine habitat and that adult males eat more roots and invertebrates than immature kea. We 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, subsequently using stable isotope mixing models, based on these kea-specific values, to establish the contribution of plant and animal matter to the kea’s diet. The diet of kea in the rainforest habitat is mainly animal-based, whereas the diet of kea in alpine habitat is mainly plant-based, and males ate eat animal matter than females in the rainforest.
Additionally, birds sampled in the rainforest have longer bills and heads than those in alpine regions, which suggests a link between kea bill and head length and foraging ecology. The relationship between bill/head length and the consumption of animal matter is especially strong in kea, and it seems that changes in the degree to which kea rely on invertebrate foraging could result in changes in their morphology. We also examined differences in the kea’s isotopic niche, finding that there is niche partitioning among male and female kea in alpine habitats.
Relevant publications
Amanda Greer and Laura Young worked on the foraging ecology and nutrient balancing of this distinctively exploratory parrot. Amanda's research was funded by the Hellaby Indigenous Grasslands Research Trust and by the Forest and Bird Society of New Zealand.
We investigated intraspecific variation in the foraging ecology of kea, and its link with variation in morphological traits. Field observations and faecal sample analyses show that kea in the rainforest habitat eat invertebrates three times as frequently as those in the alpine habitat and that adult males eat more roots and invertebrates than immature kea. We 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, subsequently using stable isotope mixing models, based on these kea-specific values, to establish the contribution of plant and animal matter to the kea’s diet. The diet of kea in the rainforest habitat is mainly animal-based, whereas the diet of kea in alpine habitat is mainly plant-based, and males ate eat animal matter than females in the rainforest.
Additionally, birds sampled in the rainforest have longer bills and heads than those in alpine regions, which suggests a link between kea bill and head length and foraging ecology. The relationship between bill/head length and the consumption of animal matter is especially strong in kea, and it seems that changes in the degree to which kea rely on invertebrate foraging could result in changes in their morphology. We also examined differences in the kea’s isotopic niche, finding that there is niche partitioning among male and female kea in alpine habitats.
Relevant publications
Amanda Greer and Laura Young worked on the foraging ecology and nutrient balancing of this distinctively exploratory parrot. Amanda's research was funded by the Hellaby Indigenous Grasslands Research Trust and by the Forest and Bird Society of New Zealand.
Kea communication
Animal communication plays a fundamental role in the study of animal cognition, yet, despite evidence that the kea has cognitive abilities rivalling that of primates, this relationship remains unexplored in what is arguably the world’s most charismatic bird. Animal signals were traditionally seen as conveying information about an animal’s internal state. Now it is accepted that many animals communicate about events and stimuli external to themselves. These ‘functionally referential signals’ should be structurally discrete and be highly stimulus specific. A clear match between the object or context associated with that signal, the referent (e.g. predator type), and signal structure, is an indication of stimulus specificity. In order to determine that a signal is functionally referential it must be shown that the discrete signal elicits in receivers a response as if the referent was present, but in its absence.
In this project we are characterising the acoustic structure and biological function of kea vocalisations, and in so doing, testing the relationship between communication and cognitive ability using a world-renowned, unique New Zealand alpine parrot as an ideal subject. Our objective is to investigate how cognitive flexibility, sociality and communication systems, and the vagaries of a unique habitat, interrelate in the kea. If habitat structure prevents discrimination between two sounds at a distance, such as, for example, dense vegetation attenuating signals, this will directly influence signal structure by selecting for relatively simple communication. Because kea venture from alpine beech forest onto snowy peaks above the tree-line, an open habitat, this study will inform us about the role of habitat structure in the use of acoustic signals by a bird with high cognitive abilities.
Spectrograms of kea calls: A. Chatter, B. Mew, C. Screech (or keeeaaa call)- contact call, D. Screech-trill, E. Trill, F. Warble - play call, G. Whistle, H: Within call harmonic variation (yellow arrows point at the harmonics). Note different timescales on X axis.
Relevant publications
Raoul Schwing was a PhD student working on this project, which was funded by the Brian-Mason Technical Trust.
Raoul Schwing was a PhD student working on this project, which was funded by the Brian-Mason Technical Trust.