Song and Territorial Behaviour of Male-Male and Male-Female Pairs of the North Island Kokako (Callaeas cinerea wilsoni)

Abstract

Male-male pairing has been previously described for captive individuals of two duetting passerines. The sexually monomorphic North Island kokako (Callaeas cinerea wilsoni) is an endangered forest bird which is declining on the mainland of New Zealand, and is the only duetting species for which male-male pairing is known to be common in wild populations. This thesis determined whether male-male kokako pairs can be distinguished from male/female pairs on the basis of song and territorial behaviour. The first study began with a detailed analysis of the contributions that male/female pair members make to duets (n=11 pairs), with a focus on their use of fundamental frequencies and the proportion of the duet that was sung by each sex. Whole male/female songs were also examined in terms of the combined fundamental frequencies used by the pair as a unit (n=16 pairs). Females typically sang less in the duet than males (8 of 11 pairs) and they had a higher song pitch than males (5 of 5 dialects examined). However, some females sang much more than others and they sang at male-typical song pitches. The duet analysis led me to predict that male-male pairs divide the duet more equally and sing less at female-dominated song pitches than male/females pairs. The predictions were then tested on confirmed (n=3) and suspected (n=6) male-male pairs. One confirmed male-male pair only met the first prediction, while one confirmed and four suspected male-male pairs only met the second prediction. One suspected male-male pair met both, and the remaining two male-male pairs ( one confirmed, one suspected) met neither of the predictions. These results are discussed in terms of being able to identify male-male pairs, and in terms of the adaptive significance of male-male pairing. Male-male pairs may be identified using the predictions, however some male/female pairs might also meet the predictions in some dialects which could limit the reliability of this as a sexing technique. The second study examined the territorial responses of male-male pairs (n=6) and male/female pairs (n=7) to determine whether kokako pairs can 'range' song and to identify other ways of distinguishing between these pair types. Pairs were presented with their own songs in an un-degraded and a degraded form, and data were recorded on intra-pair spacing, song matching, song output, and the pair's movements in relation to the speaker. Kokako showed no differences in their response to the two treatments, nor did male-male pairs respond differently to male/female pairs. These results were attributed to an insufficient sample size, and the fact that the birds were able to have close-range experience with the speaker during playback which could have provided all pairs with obvious cues to locating the source of the sound. From the outcome of the first study, I recommended that the use of the predictions be confined to non-breeding kokako pairs because of the risk of encountering females that sing male-dominated song, and that the stability of kokako song features be assessed to determine whether patterns which currently distinguish male-male from male-female pairs in a population can be applied in the long term. From the outcome of the second study, I recommended that kokako song studies should first focus on obtaining an understanding of the structure of song and of the use of individual song elements, before further playback experiments are attempted. Recommendations with regard to the use of playback in population surveying were also given, with particular regard to ensuring that the source song is coherent to the birds.