Vocal communication, behaviour and ecology of the North Island kaka (Nestor meridionalis septentrionalis) on Kapiti Island, New Zealand

Abstract

This thesis is composed of three main components. The first section is a quantitative assessment of kaka vocalisations and behaviour obtained via field observations. The second section is a playback experiment that assesses distance perception in kaka. The third is a brief assessment of productivity following the eradication of introduced predators on Kapiti Island. The diversity of vocalisations of the North Island kaka (Nestor meridionalis septentrionalis), have not previously been quantified. I investigate the vocal repertoire of kaka on Kapiti Island. The behavioural context associated with call production, in conjunction with the acoustic components of calls are assessed to determine the function of vocal diversity. Transmission experiments were conducted to determine the affects of habitat on vocal signal transmission. Transmission through habitat affects the acoustic components of calls differently (i.e. through signal attenuation and degradation), resulting in the variation of a signals transmission range. Variation amongst the acoustic properties of calls indicates that there are five different call types: schrack, schrack-who, gurgle, bark and snicker. Transmission experiments, and estimates of distances between signallers and receivers indicate that calls vary in their transmission capacities. The schrack and snicker calls are also associated with flight and copulatory behaviour, indicating function in long and short-range transmission respectively. The function of acoustic diversity in kaka vocalisations thus appears attributable to variation in transmission distances. Studies of auditory perception in songbirds indicate that song degradation, resulting from signal transmission can be used to estimate the distance of singing conspecifics (called ranging). I adopted methodologies from songbird literature on ranging to test the hypothesis that kaka calls are distance specific. I used degradation cues incorporated into playback calls to investigate whether kaka can discriminate between degraded, non-degraded and attenuated calls. I predicted that non-degraded playbacks would facilitate short-range response calls, faster response rates and more walk responses, as a conspecific would be perceived to be within close proximity. In contrast, I predicted that degraded and attenuated playbacks simulating a distant conspecific would facilitate long-range response calls, slower response rates and more flight responses. Results indicate that kaka respond with significantly more long-range calls than short-range calls under all playback conditions. Kaka were also significantly more likely to respond to degraded and attenuated playbacks than non-degraded playbacks. However, I found no difference in response call types, rates, and behaviour amongst any of the playback conditions presented. Therefore, results indicate no support for the hypothesis. Differences in perception between songbirds and parrots therefore requires a different experimental method, other than that adopted from songbird literature to be developed in order to examine the ranging abilities of parrots. Productivity of kaka after rat eradication was also assessed and compared to that before rat eradication. Low productivity is commonly observed in kaka and is thought to be primarily attributed to predation. However, previous studies indicate that productivity is also subject to inter-annual variation in plant food abundance. Interpretation of results is speculative, as many nest sites were inaccessible, limiting direct observations. However, five of the six nests located suggest that chicks failed to fledge. Productivity thus remains low. Results suggest that the main cause of nest failure in absence of introduced predators is attributable to low plant food abundance causing the starvation of nestlings.