Diploma thesis: The Long Calls of Wild Male Orangutans: A Phylogenetic Approach.

2004, The Long Calls of Wild Male Orangutans: A Phylogenetic Approach. Diploma thesis, Zoological Institute, Tierarztliche Hochschule Hannover, 74 pp.

Although several genetic, molecular, and morphological studies were carried out to clarify orangutan systematics, ongoing taxonomic controversies still exist. This project shows a new approach to orangutan phylogeny with focus on their long calls. Presented by numerous works, analyses on species-specific loud calls of primates can help to understand phylogenetic influences and to reconstruct taxonomy. Orangutan males produce long calls to regulate inter-male spacing and to attract mates.

Since samples needed to be pooled from dispersed orangutan populations and recordings from Northwest Borneo were not at my disposal, I collected the missing data myself in Batang Ai National Park, Sarawak. During this field work, 4.3 long calls were heard a day [+ or -] at least 290% more calls than anywhere else reported. This rate reflects a high population density due to the profusion of empili fruit (Lithocarpus sp.). Additionally, compared to other populations, Batang Ai orangutans vocalize more often during the night. Presumably, this time offers males of lesser rank the opportunity to compete acoustically with more dominant individuals.

Prior to measuring sonagrams, the call structure was examined, revealing that orangutans are able to emit synchronic notes, possibly by means of their huge laryngeal sacs.

In this project, 64 variables (qualitative: n = 4; numerical: n = 26; metrical: n = 34) of 75 long calls from ten populations of wild orangutans (Borneo: n = 5; North Sumatra: n = 5) were analyzed. Hereby, all four possibly geographically isolated Bornean groups were represented. Their outcomes do not support nor reject island bifurcation. Monophyletic groups were found for Northwest Borneo (72-73%), Northeast-East Borneo (73-85%), and Ketambe (74-78%).

Although there are some inconsistencies that may be explained by further inquiries into long calls, long call analysis is an appropriate way to study orangutan phylogeny. As proposed by the Orangutan Action Plan, this study indicates for conservation management to separately deal with orangutans from geographically isolated areas (Northwest, Northeast, East, and Southwest Borneo; North and South Sumatra). Still, additional phylogeographic works are needed for more effective support (author's abstract, www.tiho-hannover.de).