The current worldwide studbook of pileated gibbons (Hylobates pileatus) reflects a skewed sex ratio towards males and poor reproduction. Thus, the captive population is threatened to become overaged and extinct without facilitating reproduction in the near future. Several factors are likely to contribute to the poor breeding success. Environmental factors such as management and housing condition, health related problems, social factors, and/or chronic stress have been shown to have a major impact on primate reproduction. The present study evaluated all 12 current European facilities housing pileated gibbons in relation to husbandry, management and fecal glucocorticoid output to assess the potential impact of these factors for pileated gibbon breeding.
Enrichment and size of inside enclosure appeared to have a positive influence on reproduction while visitor access did not seem to have an influence. In addition, reproductively active pairs performed singing duets more frequently than non-reproducing pairs, and reproductively active females had regular visible menstruations in contrast to females that did not breed. Non-reproducing animals exhibited higher fecal stress hormone levels compared to reproducing animals. Remarkably, hand-reared animals also had higher fecal glucocorticoid levels.
Summarizing current results, it seems that careful selection of compatible pairs in combination with improvements in husbandry and management may reduce potential stress for the animals and thus may represent a basis for enhanced breeding. The small population size might require the import of unrelated and socially competent animals, especially females, to maintain a stable captive population in Europe and to prevent inbreeding in the future.
The authors thank all participating pileated gibbon facilities, curators, and keepers for their special care of the animals and help with this work. The work, support, and advice of Ms. Andrea Heistermann in all the laboratory techniques are gratefully appreciated.