Vocalisations of the New Zealand morepork (Ninox novaeseelandiae) on Ponui Island : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Zoology at Massey University, Palmerston North, New Zealand
Vocalisations provide an effective way to overcome the challenge of studying the behaviour of cryptic or nocturnal species. Knowledge of vocalisations can be applied to management strategies such as population census, monitoring, and territory mapping. The New Zealand Morepork (Ninox novaeseelandiae) is a nocturnal raptor and, to date, there has been little research into their vocalisations even though this offers a key method for monitoring morepork populations. Although not at risk, population monitoring of morepork will help detect population size changes in this avian predator which may prey on native endangered fauna and may suffer secondary poisoning.
This study investigated the vocal ecology of morepork on Ponui Island, Hauraki Gulf, New Zealand from April 2013 to April 2014. The initial goal was to develop a monitoring method for morepork. However, due to a lack of detailed basic knowledge of their vocalisations, the primary objective shifted to filling that knowledge gap and providing baseline data for future research. The aims of this study were thus to characterise all of the calls given by the morepork on the island; to investigate spectral and temporal parameters of three main calls; to plot the amount of calling across a night and a year; and to study the responses of morepork to playback calls.
Eight morepork were caught using mist-nets and subsequently tracked by radio-telemetry. Vocalisations were recorded using manual and automatic digital sound recorders and calls were analysed with manual and automated sound analysis software. I described eleven distinct calls, referred to as more-pork, trill, rororo, more-more-pork, weow, low trill, copulation squeal, single hoot, distress squeak, chicketting and juvenile begging trill and I further analysed the spectral and temporal characteristics of three main calls, more-pork, trill and rororo. I found variation between individual morepork in acoustic parameters of these call types. I found no evidence of sexual variation in the fundamental frequency, fundamental duration nor inter-syllable duration of the three call types. However, sample sizes were small (2 males to 7 females) and a larger sample size would be needed to confirm these results.
The average number of all morepork call types showed temporal variation both nightly and monthly. A low amount of calling in winter months compared to summer
appeared to coincide with the morepork breeding cycle. The highest numbers of call were heard from November to January, with the numbers of calls during this period being significantly higher than in all other months. The number of calls per hour showed two peaks: one around the middle of the night and the other during the last hour of darkness. The number of calls heard in the first two hours after sunset were significantly lower than during the rest of the night.
Playbacks were effective in eliciting responses from morepork, but the proportion of responses to playback was lower than to natural calls. Response rates did not seem to be affected by season. Session time and order of playback had an effect on proportional responses as well as playback call-type whereby rororo elicited the most responses and trill elicited the fewest.
This project broadened our knowledge of morepork vocal ecology and therefore contributes to our knowledge of raptor vocal communication. The study also presents information and recommendations that will be useful to future research and also in management of morepork. In particular, this project provides background information needed to help develop protocols for acoustic monitoring of morepork. The techniques used in this study and the general results can be used or applied to studies of other nocturnal species.