Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.08.21.260679v1?rss=1 Authors: Vaglio, S., Kaburu, S., Young, C., Pearce, R., Smith, S., Tompkins, B. E., Elwell, E., Fontani, S., Marliani, G., Accorsi, P. A. Abstract: Almost half of the primate species recognized today worldwide are classified as endangered or critically endangered in the wild. Captive breeding is vital for primate conservation, with modern zoos serving a crucial role as breeders of populations acting as buffers against extinction, ambassadors of endangered species, and educators of the general public. However, captive populations may experience welfare issues that may also undermine their breeding success. In order to design and test a new scent enrichment programme to enhance the breeding success and well-being of critically endangered zoo primates, we carried out a preliminary study to assess the effects of lavender on captive red-ruffed lemurs ( Varecia rubra ) and Lar gibbons ( Hylobates lar ) as these species presently show a low success rate in captive breeding and are critically endangered in the wild. We combined behavioural observations and faecal endocrinology analyses to assess the effects of lavender on two captive troops (N = 8) housed at Dudley Zoo and Castle (UK). We recorded observations of natural species-specific and abnormal stress-related behaviours for 144 hr using instantaneous scan sampling. We collected 78 faecal samples and measured the faecal cortisol concentrations using radioimmunoassay. We found a significant effect by the scent enrichment on social interactions and stress-related behaviours (i.e., pacing and self-scratching), with both species reducing their rates of stress-related behaviours after they were exposed to lavender. We also found that both species displayed a significant increase in faecal glucocorticoids following the exposure to lavender. Our findings suggest that lavender may work as scent enrichment to decrease the stress levels of zoo primates across the major lineages, but its effects might change depending on the species-specific social lives and olfactory repertoires of primates. Copy rights belong to original authors. Visit the link for more info