The role of middens in white rhino olfactory communication

Abstract

White rhinos (Ceratotherium simum) use dung odours to transmit information about their sex, age, territorial status (males) and oestrous state. Moreover, as white rhinos defecate in communal middens (i.e. dung heaps, or latrines) it has been suggested that these middens may act as information centres.However, it is uncertain which individuals primarily transmit information via middens, or for whom this information is intended. Using video-recording camera traps, we investigated the behaviour of white rhinos at middens. We hypothesised that territorial adult males would visit, defecate, and sniff other dung more than other adults. In line with this, we found that they visited and defecated more than other individuals. Moreover, territorial males and potential male challengers were the main individuals to investigate dung piles. These olfactory investigations focused primarily on territorial male and adult female dung (male-male and female-male communication). Adult females and subordinate males also investigated territorial male and female dung as much as other males did, suggesting male-female and female-female communication. In addition to olfactory signals, there was a spatial aspect to midden use, where territorial males defecated only in the centre of a midden, while other individuals defecated primarily around the periphery. Yet, subordinate males also tended to defecate in the centre, suggesting an indication of residency. Lastly, territorial males defecated more 2 frequently than any other adult, and were able to do so by regulating their dung output (i.e. producing smaller volumes). Our results indicate that middens act as information centres, where the primary function seems to be for territorial males to transmit and obtain information. However, non-territorial males may also assess female reproductive state, while females may be assessing the quality of all males, and the number of other females using a midden. Ultimately, our results highlight the importance of middens in white rhino communication.

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

“…If this were the case, then the impact of reduced signal longevity could be minimised, and the probability of individuals visiting the midden and detecting the olfactory signals increased. However, more recent evidence indicates that territorial males only defecate in the same midden on average once every ten days (Marneweck et al 2018). Compounded with this, white rhino dung odours only last for a couple of days (Marneweck et al 2017b).…”

“…As dung is a limited resource, the likely reason that territorial males are not increasing the frequency at which they remark middens is that they are already defecating at the maximum frequency permitted by their physiology. Moreover, it seems that males attempt to maximise the spatial distribution of their dung across the >30 middens they can have in their territories (Owen-Smith 1973) by limiting how much they deposit at any one midden (Marneweck et al 2018).…”

“…These middens are located at strategic locations including territory boundaries, well-travelled rhino paths, and next to water sources (Owen-Smith 1973), which increases encounter probability. The primary function of middens is for territorial males to advertise territory ownership (male-male communication) and find reproductive females (female-male communication) (Marneweck et al 2018). However, secondary functions likely include non-territorial males locating reproductive females for sneaky copulations, females to assess male quality (male-female communication), and potential challengers to assess both the territorial male and territory quality (Marneweck et al 2018).…”

“…Territorial males defecate in the centre, while non-territorial males, adult females, and younger animals primarily defecate around the edge (Owen-Smith 1973;Marneweck et al 2018). This spatial distribution of dung may increase the detectability of the signals from these different individuals (Marneweck et al 2018). Yet, within these middens, territorial males are the only individuals to scatter their dung, which they do with backward kicking motions of their hind feet (Owen-Smith 1971) (Supplementary video).…”

“…As one of the main functions of middens is communication from territorial males (i.e. male-male and male-female communication ;Marneweck et al (2018)), it is possible that these males kick their dung to enhance their olfactory signals (i.e. OSA).…”