The Acoustic Signal Pathway of the Kea (Nestor notabilis)

Abstract

The kea (Nestor notabilis) is an endemic parrot of the Southern Alps region of the South island of New Zealand. Despite mounting interest in its cognitive abilities, its natural behaviour, including its communication system, is poorly understood. The kea’s main signal pathway for the intraspecific exchange of information is vocal communication. The aim of this thesis was to investigate kea vocal communication by testing the factors necessary for the successful transfer of acoustic information from sender to receiver: production, structure, transmission, perception, and the behavioural effects of signal reception. Vocal organs (syrinxes) of the kea, along with the syrinx of the related kaka (Nestor meridionalis), were investigated for the purpose of describing their anatomy and gaining insight into the production of calls. Although the syrinxes were very similar to those of other parrots, some structures more closely resembled those of falcons, supporting the recently proposed Eufalconimorphae clade (parrots, falcons, passerines). Additionally, 2884 calls from wild kea were categorized into seven structurally-distinct types (chatter, mew, screech, screech-trill, trill, warble and whistle) based on acoustic parameters. Subsequent playback experiments to test the environmental effects of call transmission from two different habitats, Arthur’s Pass (forested) and Aoraki/Mount Cook (open) National Parks, showed effects of broadcasting and receiving height, call type and call origin on call transmission across a range of distances, and strongly supported the area around 3 kHz as the most important for kea communication. A behavioural discrimination task was then conducted with captive kea to test hearing sensitivity. The kea’s ability to perceive sounds at different frequencies and amplitudes closely matched those found among other avian species, and provided further support for the importance of the 3 kHz frequency in their acoustic communication. A steeper drop-off in sensitivity below 1 kHz was attributed to high levels of wind noise in their habitat. Finally, a field playback experiment exploring behavioural changes associated with hearing the warble play call showed that this call specifically elicits play behaviour, even among solitary individuals. This first comprehensive study of kea communication provides key information on the natural behaviour of this charismatic, but highly threatened, species.