The role of middens in white rhino olfactory communication

Mountain gazelles' (Gazella gazella) males use mutual dung middens in favorable locations

Males of the mountain gazelle deposit dung middens (different colors and shapes represent middens of different haplotypes) in preferable forest plots and countermark the same middens (two color circles) at the boundaries of their territories.

Chemical communication and its role in sexual selection across Animalia

Sexual selection has been studied as a major evolutionary driver of animal diversity for roughly 50 years. Much evidence indicates that competition for mates favors elaborate signaling traits. However, this evidence comes primarily from a few taxa, leaving sexual selection as a salient evolutionary force across Animalia largely untested. Here, we reviewed the evidence for sexual selection on communication across all animal phyla, classes, and orders with emphasis on chemoreception, the only sense shared across lifeforms. An exhaustive literature review documented evidence for sexual selection on chemosensory traits in 10 of 34 animal phyla and indications of sexual selection on chemosensory traits in an additional 13 phyla. Potential targets of sexual selection include structures and processes involved in production, delivery, and detection of chemical signals. Our review suggests sexual selection plays a widespread role in the evolution of communication and highlights the need for research that better reflects animal diversity.

Brown bear skin-borne secretions display evidence of individuality and age-sex variation

Scent originates from excretions and secretions, and its chemical complexity in mammals translates into a diverse mode of signalling. Identifying how information is encoded can help to establish the mechanisms of olfactory communication and the use of odours as chemical signals. Building upon existing behavioural and histological literature, we examined the chemical profile of secretions used for scent marking by a solitary, non-territorial carnivore, the brown bear (Ursus arctos). We investigated the incidence, abundance, and uniqueness of volatile organic compounds (VOCs) from cutaneous glandular secretions of 12 wild brown bears collected during late and post-breeding season, and assessed whether age-sex class, body site, and individual identity explained profile variation. VOC profiles varied in the average number of compounds, compound incidence, and compound abundance by age-sex class and individual identity (when individuals were grouped by sex), but not by body site. Mature males differed from other age-sex classes, secreting fewer compounds on average with the least variance between individuals. Compound uniqueness varied by body site and age for both males and females and across individuals. Our results indicate that brown bear skin-borne secretions may facilitate age-sex class and individual recognition, which can contribute towards further understanding of mating systems and social behaviour.

Cheetah marking sites are also used by other species for communication: evidence from photographic data in a comparative setup

Many mammalian species communicate via olfactory communication placed at particular locations. The majority of these studies focused on intraspecific communication. More recently, studies have also investigated interspecific communication and recorded prey animals sniffing olfactory cues left by predators and predators investigating or counter-marking cues left by other predator species. The purpose of exchanging olfactory cues within a species community is little understood. Using a comparative study design, we investigated the behaviour of a mammalian community at cheetah marking trees and paired control trees using camera traps on Namibian farmland. We tested the predictions derived from hypotheses regarding the reasons for visits to the marking trees. Cheetah marking trees and control trees were visited 1101 times by 29 mammalian species (excluding cheetahs), with more species recorded at the marking trees than control trees. Two competitively subordinate carnivore species made more visiting and sniffing events, respectively, at cheetah marking trees than control trees, possibly to assess the time since cheetahs were in the area. Two opportunistic scavenger species sniffed more frequently at the marking trees than control trees, perhaps to feed on undigested prey remains in scats. One common prey species of cheetahs had fewer visiting events at the marking trees than control trees, likely to reduce encounters with cheetahs. Further, one species that is rarely preyed by cheetahs marked cheetah marking trees at the same frequency as control trees, suggesting it uses conspicuous sites rather for intraspecific than interspecific communication. Thus, trees used by cheetahs for marking also play an important role in olfactory communication for a variety of mammalian species.

White rhinos and other herbivores decrease visitations and increase vigilance in response to human vocalizations

Harnessing the fear animals have of humans has the potential to aid in the conservation of wildlife. Most vertebrates perceive humans as “super predators.” While predator cues are an important nonlethal management tool, the use of human cues for management has rarely been implemented or experimentally tested. Extensive poaching is threatening the persistence of white rhinos (Ceratotherium simum simum), and there is a need to deter them from areas with elevated poaching risks. To investigate the feasibility of harnessing the fear white rhinos have of humans to aid in their conservation, we conducted playback experiments at rhino middens. We broadcasted repeated human (treatment) and bird (control) vocalizations, and measured changes in visitations and antipredator responses. We found that overall rhino visitations did not change in response to controls but decreased by 46% in response to human vocalizations. This pattern appears to be driven by the response of females, who decreased their visitations by 70% in response to human vocalizations, while visitations by males remained unchanged. This difference is likely related to males defending small exclusive territories. Providing evidence that changes in female visitation rates were a function of the perceived fear of white rhinos, we found that both sexes exhibited more vigilance in response to human vocalizations (males 69.5%, females 96%) compared to controls. We also saw a 63% reduction of other herbivores at treatment sites. Our findings provide evidence that the fear of humans can be used to alter the movements and behavior of female white rhinos, critical for population recovery, as well as other large herbivores.

JA, Hewitt DG, Campbell TA. Latrine ecology of nilgai antelope

The use of scent for communication is widespread in mammals, yet the role of scent-marking in the social system of many species is poorly understood. Nilgai antelope (Boselaphus tragocamelus) are native to India, Nepal, and Pakistan. They were introduced to Texas rangelands in the United States during the 1920s to 1940s, and have since expanded into much of coastal South Texas and northern Mexico. The nilgai social system includes the use of latrines or repeated defecation at a localized site. We quantified and described physical and behavioral characteristics of nilgai latrine ecology to investigate drivers of latrine use at three sites in South Texas, during April 2018 to March 2019. Latrines were abundant (2.6–8.7 latrines/ha on unpaved roads, 0.4–0.9 latrines/ha off-roads), with no evidence for selection as to vegetation communities; latrines were dynamic in persistence and visitation rates. We found higher densities of latrines in Spring surveys, just after the peak of nilgai breeding activity, compared to Autumn surveys. Density of nilgai latrines was 3–10 times greater than estimated population densities, indicating individual nilgai must use multiple latrines. Camera traps and fecal DNA analysis revealed latrines were mainly (70%) visited by bulls and defecated on by bulls (92% in photos, 89% for DNA samples). The greatest frequency of visits occurred during the peak in the nilgai breeding season, from December–February; latrines were visited every 2–3 days on average. Body characteristics of photographed individuals and genetic analysis of feces indicated repeated visits from the same individuals. Nilgai cows occasionally used latrines; their use was sometimes followed by bulls showing flehmen responses after a female defecated or urinated on the latrine. We propose that dominant bulls use latrines for territory demarcation to display social dominance to both cows in estrus and subordinate bulls. Cows likely use latrines to communicate reproductive status. This study is the first intensive assessment focused on latrine ecology in nilgai. Our results directly contradict anecdotal descriptions of latrine use and behavior in nilgai but are consistent with predictions of antelope social systems based on body size, feeding type, and group dynamics.

Why wait to mark? Possible reasons behind latency from olfactory exploration to overmarking in four African equid species

Whereas most studies on overmarking in mammals analysed the rate of overmarking, that those investigate time between exploration of an olfactory stimulus and the response to it remain less common, with inconsistent results. We examined the latency in time between elimination by the sender and sniffing by the receiver, and from sniffing and overmarking, in four captive African equid species to explore differences among species, and among age and sex classes. We investigated these latency time periods in light of three potential hypotheses explaining overmarking behaviour in equids: social bonds, group cohesion, and intrasexual competition. Analysing 1684 events of sniffing and 719 of overmarking among 130 individuals, we found that (i) the time from elimination to overmarking was shorter among female friends and in parent-offspring dyads, proving support to the social bond hypothesis; (ii) intraspecific differences in time periods do not reflect the social organisation of species, thus not supporting the group cohesion hypothesis; (iii) males were more attracted to elimination of conspecifics than females, and female's eliminations were inspected longer, in line with the sexual competition hypothesis and/or reproductive behaviour. In addition, we found that the younger foals came to sniff eliminations faster than older ones, and in larger groups foals devoted longer time to sniffing the elimination before overmarking. We concluded that examination of the elimination could be driven by motivations other than the decision to overmark. Whereas overmarking serves to express bonds to a familiar individual, the latency of overmarking reflects more reproductive interests.

Female Southern White Rhinoceros Can Select Mates to Avoid Inbreeding

Current management models for many endangered species focus primarily on demographic recovery, often ignoring their intrinsic ecological requirements. Across the protected area network of southern Africa, most southern white rhinoceros are managed in populations of less than 50 individuals, experiencing restricted dispersal opportunities, and limited breeding male numbers due to their exclusive home range requirements. In the absence of information on the breeding structure of these populations, poor management decisions may require females to either forego a breeding opportunity or select to inbreed with close relatives. Here, we use a combination of social pedigree data together with genetic analyses to reconstruct the parentage of all 28 offspring produced in a 5-year period in a managed free-ranging southern white rhinoceros population. During this period, all breeding females (founders and first-generation daughters) had access to both a founder male (father to most of the daughters) and two recently introduced inexperienced males. We report that while founder females were more likely to breed with the founder male, their daughters, in contrast, were more likely to breed with the introduced males, thus avoiding inbreeding. However, we also found evidence of father-daughter inbreeding in this population, and contend that in the absence of choice, rather than forego a breeding opportunity, female white rhinoceros will inbreed with their fathers. We argue that to effectively conserve the southern white rhinoceros, managers need to understand the breeding structure of these small populations, particularly in terms of parentage and kinship.

The female effect-how female receptivity influences faecal testosterone metabolite levels, socio-positive behaviour and vocalization in male Southern white rhinoceroses

Testosterone is known to be essential for sexual maturation as well as for the display of behavioural traits linked to reproduction. At the same time, external factors such as the presence of receptive females may affect testosterone levels, stressing the hormone's substantial role in reproductive success. It is therefore of major interest to investigate the links between androgens, behaviour and the social environment especially in species that rely on a resilient reproduction rate, such as the white rhinoceros (WR). We collected faecal samples of 16 male Southern WR (Ceratotherium simum simum) aged between 1 and 44 years from 11 European zoos. Audio and video recordings were simultaneously taken from five of the study males that were sexually mature and had direct contact with receptive females. Our results showed a positive correlation of faecal testosterone metabolite (fTM) concentrations and progressing age up until adulthood followed by a decline in older males. While previous reproductive success did not show any effect, the access to receptive females resulted in higher fTM levels. Thereby, fTM concentrations remained at the same level regardless of the receptivity phase, while social cohesion with respective females, affiliative behaviour as well as call rates of Pant and Hiss distinctly peaked during the receptive compared to the non-receptive periods. Conclusively, the immediate presence of receptive females poses a female effect that enhances the overall androgen levels in males and, thus, might facilitate their reproductive success. However, androgens do not seem to be the main driver of behavioural changes during courtship or mating. By linking endocrinological and socio-behavioural factors, we were able to provide an applicable basis for non-invasive monitoring of reproductive behaviour in male WR in captivity, thereby contributing to deeper understanding of potential reproduction impairments in a species whose population in captivity remains not fully self-sustaining.

Intestines of non-uniform stiffness mold the corners of wombat feces

The bare-nosed wombat (Vombatus ursinus) is a fossorial, herbivorous, Australian marsupial, renowned for its cubic feces. However, the ability of the wombat's soft intestine to sculpt flat faces and sharp corners in feces is poorly understood. In this combined experimental and numerical study, we show one mechanism for the formation of corners in a highly damped environment. Wombat dissections show that cubes are formed within the last 17 percent of the intestine. Using histology and tensile testing, we discover that the cross-section of the intestine exhibits regions with a two-fold increase in thickness and a four-fold increase in stiffness, which we hypothesize facilitates the formation of corners by contractions of the intestine. Using a mathematical model, we simulate a series of azimuthal contractions of a damped elastic ring composed of alternating stiff and soft regions. Increased stiffness ratio and higher Reynolds number yield shapes that are more square. The corners arise from faster contraction in the stiff regions and relatively slower movement in the center of the soft regions. These results may have applications in manufacturing, clinical pathology, and digestive health.

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

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.