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 hypothesized 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). Although investigating less often, investigation by adult females and subordinate males was also focused on territorial male and female dung, 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 frequently than any other adult, and were able to do so by regulating their dung output (i.e. producing smaller volumes per deposit). 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, nonterritorial 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.