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

Abstract

Many mammals enhance their olfactory signals visually by depositing them in conspicuous locations such as well-travelled paths. It is also possible to enhance the odour itself through behaviours aimed at modifying odour emission rates. White rhinos defecate in communal middens. While defecating, territorial males kick sharply with their back feet which disperses their dung. Despite being a ubiquitous trait of territorial male white rhinos, the reason behind this behaviour is unclear. We hypothesised that the purpose of dung kicking was for olfactory signal amplification (OSA) in terms of an increased emission of volatile compounds (i.e. increased signal strength). Using dung collected from non-territorial adult males (because it is not possible to collect whole dung from territorial males), we show that the dispersal of male white rhino dung causes OSA by increasing the emission of hydrocarbon acids. The dung odour of territorial and non-territorial males differs only quantitatively, hence it is likely that the same emission patterns occur for territorial male dung odours following dung dispersal. The volatile compound indicating age of intact dung was toluene, but for dispersed dung it was acetophenone (similar to territorial male dung). Despite the benefits of OSA, dung dispersal carried a cost of decreased odour longevity. Thus, signal detectability is temporally reduced. However, territorial males likely counteract this by defecating in middens both before and during peak visitation times by other individuals (15:00-23:00). As a result, we suggest that dung kicking by territorial males amplifies signal strength, such that their dung odours are the most prominent and easily detectable by individuals visiting the middens. This would then better signal territorial ownership to both potential rivals and potential mates.

Links Between Feeding Preferences and Electroantennogram Response Profiles in Dung Beetles: The Importance of Dung Odor Bouquets

“…Our EAG results showed strong dung beetle responses to ρ-cresol, 1H-indole, and skatole, but also suggested that other compounds, such as nonanal, acetophenone, and ρ-cymene, may also be involved in a ‘ generalized dung bouquet ’. Acetophenone, which was only identified in horse dung in our study, has previously been identified in dung samples of cows (Laor et al 2008 ), pigs (Blanes-Vidal et al 2009 ), and several wild vertebrates (Apps et al 2012 ; Marneweck et al 2017 ; Martín et al 2010 ; Stahl et al 2015 ), indicating that this may also be a general component of dung. Other electrophysiological and behavioral studies on dung beetles have shown the importance of compounds such as ρ-cresol, indole, and skatole in dung beetle responses (Frank et al 2018b ; Inouchi et al 1988 ; Shibuya and Inouchi, 1982 ; Weithmann et al 2020 ).…”

“…This compound has been found in several dung types, including dog, white rhino, red deer, wild boar, fox, and sheep (Arnould et al 1998 ; Dormont et al 2010 ; Frank et al 2018b ; Marneweck et al 2018 ). The compound 6-methyl-5-hepten-2-one, absent in rabbit dung, has been identified in various other dungs (Marneweck et al 2017 ; Murphy et al 2012 ; Raman et al 2013 , see also Goodrich et al 1981 ). Rabbit dung was the most chemically distinctive, with several exclusive VOCs, such as the monoterpenes camphene, 1,8-cineole, and verbenone (Table 2 ) (see Couch et al 2015 ; Marneweck et al 2017 ; Pillai et al 2010 ; Raman et al 2013 ).…”

“…The compound 6-methyl-5-hepten-2-one, absent in rabbit dung, has been identified in various other dungs (Marneweck et al 2017 ; Murphy et al 2012 ; Raman et al 2013 , see also Goodrich et al 1981 ). Rabbit dung was the most chemically distinctive, with several exclusive VOCs, such as the monoterpenes camphene, 1,8-cineole, and verbenone (Table 2 ) (see Couch et al 2015 ; Marneweck et al 2017 ; Pillai et al 2010 ; Raman et al 2013 ). Interestingly, rabbit dung contained a high content of 1,8-cineole, which is considered a toxin to some herbivorous marsupials, necessitating metabolism and excretion (McLean and Foley 1997 ).…”

“…The SIMPER analysis, performed to explore if distinct sensory profiles of the groups of species can be attributed to a specific or set of EAG-active compounds, showed that a subset of compounds elicited strong dissimilarities among the feeding preference groups (Table3). Of these EAG responses, nonanal and sabinene has been found in several dung types, including dog, white rhino, red deer, wild boar, fox, and sheep (Arnould et al 1998;Dormont et al 2010;Frank et al 2018b;Marneweck et al 2018). The compound 6-methyl-5-hepten-2-one, absent in rabbit dung, has been identified in various other dungs (Marneweck et al 2017;Murphy et al 2012;Raman et al 2013, see also Goodrich et al 1981).…”

African elephants can detect water from natural and artificial sources via olfactory cues

“…Nevertheless, the fact that the elephants in our study were able to detect water olfactorily opens the possibility that they, especially with their exceptional sense of smell (Niimura et al 2014;Shoshani and Foley 2000;Shoshani et al 2006), may be able to detect water sources at distances beyond their visual range. Moreover, the VOC's being given off by the larger surface area of a body of water would likely be greater than those emitted from the small surface area of the beakers we used in our experiment (Aydin et al 2014;Marneweck et al 2018).…”