Abstract:
Geographic variation in song dialects has been described in many avian species. Few studies have examined how dialectual differences may affect pair formation between birds from geographically isolated populations translocated to one site. The endangered North Island kokako, Callaeas cinerea wilsoni, exists in approximately 15 isolated populations that each exhibit distinct dialectual variation. Kokako from six populations were translocated to Kapiti Island, New Zealand, between 1991 and 1997 for conservation purposes. This provided an opportunity to study whether dialects, which evolved at each area of origin, act as barriers to mate selection and ultimate pair formation between kokako from different origins. Between November 1999 and March 2001 tape recordings of songs were obtained from site-attached pair-bonded male kokako on Kapiti Island. Further recordings were obtained from the Department of Conservation, which included recordings of males on Kapiti Island made in previous years, as well as recordings made at areas of origin.
Given the number of birds present, results indicate that kokako have preferentially selected mates from the same area of origin, resulting in lower occurrences of pairs than would be expected. Song analysis indicated that kokako songs were typical of their areas of origin at the time of translocation and were distinct from songs from different origins. Female kokako are likely to have chosen males from the same origin as themselves as those male's syllable repertoires would reflect the acoustic environment that females experienced prior to translocation. Female kokako born on Kapiti Island did not choose mates with syllable repertoires similar to those of their fathers, indicating that female song preference develops during the transient months following fledging. Consequently, the positive assortative mating on Kapiti Island may be a temporary phenomenon following translocation that will not continue following juvenile recruitment.
During successive breeding seasons, kokako with territorial neighbours have changed their syllable repertoire composition by adding and eliminating syllables in accordance with the repertoires of their neighbours, resulting in greater syllable sharing among neighbouring birds. Male kokako born on Kapiti Island also learn their syllable repertoires from neighbours following territory establishment. The repertoires of kokako with no territorial neighbours remained unchanged. Kokako in natural populations are present in dialect groups whereby territorial neighbours share most syllables and adults are not known to change their syllable repertoires once learned. The findings of this study suggest that when kokako are presented with new syllables in adulthood they have the ability to learn such syllables, suggesting that they are 'open-ended learners'.
