Temporal Variation of White Rhino Dung Odours

Abstract

In order for an olfactory signal to be effective, it must persist in the environment for an extended period. White rhino dung odours transmit information about sex, age, territorial and oestrous states. As these odours relay important information, temporal changes in the odour emission rate and/or composition may be critical in order for other individuals to obtain this information. Here, we examine how the dung odours of adult white rhinos (male: territorial and non-territorial; female: oestrous and non-oestrous) change over the short (hours) and long (seasons) term using headspace extraction. Additionally, we measure seasonal midden visitation and defecation frequency to link behaviours to seasonal changes in odour longevity. We found that during the dry season, territorial male dung odours persisted for 48 hours, while the odours of all other adults persisted for >48 hours. The high temperature and humidity of the wet season did not affect odour longevity of oestrous females, but decreased dung odour longevity (i.e. increased emission) of territorial males, non-territorial males, and non-oestrous females. Despite this reduction, neither males nor females adjusted their seasonal visitation or defecation frequency. With regard to a temporal indicator, 3,7-dimethly-1,6-octadiene signalled dung age during the wet season, while acetophenone signalled dung age during the dry season. Ultimately, our results provide the first detailed account of temporal changes of dung VOCs, and highlight the limitations of dung as a signalling medium.

Ritualised Dung Kicking by White Rhino Males Amplifies Olfactory Signals but Reduces Odour Duration

“…Here, we identified a change in the most important VOC predictor for dung age of non-territorial male during the dry season. When intact, toluene is the most important VOC, as described in Marneweck et al (2017b). However, when dispersed, acetophenone is the most important VOC.…”

“…Acetophenone is the most important VOC for indicating the age of territorial male dung during the dry season (Marneweck et al 2017b). Here, we identified a change in the most important VOC predictor for dung age of non-territorial male during the dry season.…”

“…Thus, dispersal causes changes leading to odour similar to that from territorial male dung. Toluene is a benzenoid compound, and benzenoids are common VOCs emitted from plants and thus represent undigested plant material in white rhino dung (Osbourn and Lanzotti 2009;Marneweck et al 2017b). Acetophenone is a ketone, a VOC also highlighted as important in beaver (Castor canadensis) castoreum scent-marks (Müller-Schwarze and Houlihan 1991).…”

“…We then relocated the bolus to the research camp where we collected subsequent odour samples at 6, 12, 24, and 48 hours from time of defecation. We chose these times based on Marneweck et al (2017a) and Marneweck et al (2017b), where changes occur rapidly during the first 12 hours and persist for approximately 48 hours. In between sampling intervals, we left the dung outside on natural substrate (short grass), unprotected, to allow natural degradation to occur.…”

“…We controlled for individual rhino identity as a random factor in all candidate models. We did not include VOC functional group alone because it is uninformative as each functional group contribution varies considerably (Marneweck et al 2017b).…”