Temporal changes in cultural diversity across a growing meta-population of North Island saddleback (tīeke; Philesturnus rufusater) : effects of mixed versus single-source translocations : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Science in Biology at Massey University, Auckland, New Zealand
Loading...
Date
2021
DOI
Open Access Location
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Massey University
Rights
The Author
Abstract
Songbirds, the largest Order of birds, have intrigued humans for centuries given their ability to learn and produce melodious song. However, humans have also caused irreparable damage to many oscine passerines via the introduction of invasive mammalian predators. This is most apparent in New Zealand, where its distinctive avifauna have been decimated by induced species. Historical conservation efforts have done well to preserve and increase the populations of many remaining indigenous species, but the consequences of these actions on the song diversity and overall song culture of our endemic songbirds are poorly understood. The North Island (NI) saddleback (tīeke; Philesturnus rufusater) is an endemic social passerine that provides an excellent study species to examine such consequences given its well-recorded conservation history. Recent conservation translocations of the NI saddleback have been conducted with emphasis on maximising song diversity of populations, however, no empirical evidence currently exists showcasing whether the management practices employed have had the desired outcome. Using historic recordings of Male Rhythmical Song (MRS) – a conspecific reignition signal responsible for distinctive NI saddleback song culture - in conjunction with new recordings of MRS from three culturally distinct populations with unique translocation histories, my thesis examines current and historic conservation management policies and their potential consequences for NI saddleback song culture. I first examined whether a translocation strategy employed at Shakespear Regional park (which involved the simultaneous release of birds from two culturally distinct source populations) achieved the desired outcome of maximising cultural complexity in a new population. I found that first-generation males learned source population MRS types, but no male sang MRS from both source populations. Also, rapid innovation of MRS was identified at Shakespear, where many young males innovated their own MRS irrespective of their proximity to an adult social tutor. There was evidence of culturally distinct song neighbourhoods forming one-year post-translocation, and although assortative pairing did occur, females did not exclusively pair with males from the same source population. This signifies that MRS is not solely sufficient enough to act as a pre-mating barrier between NI saddleback of different cultures. I then examined how song culture changes over a discrete timeframe in the Motuihe Island population of NI saddlebacks. I found that population-level song repertoire, cultural diversity, and song variability all increased dramatically in 11 years. The immense changes to Motuihe’s song culture can be explained by the cultural bottleneck and cultural mutation hypotheses. My work indicates that consideration must be made on the future restoration initiatives of new sites if conservation translocations aim to conserve ancient dialects in NI saddleback. Finally, I examined how acoustic characteristics of MRS vary between populations and correlate with the translocation history of each population. My main finding was that populations that have undergone more serial translocations have lower song diversity, and drivers for the development of these distinct acoustic signatures are a result of cultural bottlenecks, cultural drift and cultural mutations in relation to each population’s unique translocation history. Although I expected populations that were established from a multi-sourced founder group to have higher cultural complexity than serially translocated populations of a similar age, population bottleneck events experienced during my project inhibited this. This highlights the ongoing need for the control and eradication of introduced mammalian predators, not only to conserve NI saddleback culture, but the species as a whole.