No abstract

Scent-mediated communication is considered the principal communication channel in many mammal species. Compared with visual and vocal communication, odors persist for a longer time, enabling individuals to interact without being in the same place at the same time. The brown bear (Ursus arctos), like other mammals, carries out chemical communication, for example, by means of scents deposited on marking (or rub) trees. In this study, we assessed rub tree selectivity of the brown bear in the predominantly deciduous forests of the Cantabrian Mountains (NW Spain). We first compared the characteristics of 101 brown bear rub trees with 263 control trees. We then analyzed the potential factors affecting the density of rub trees along 35 survey routes along footpaths. We hypothesized that: (1) bears would select particular trees, or tree species, with characteristics that make them more conspicuous; and (2) that bears would select trees located in areas with the highest presence of conspecifics, depending on the population density or the position of the trees within the species’ range. We used linear models and generalized additive models to test these hypotheses. Our results showed that brown bears generally selected more conspicuous trees with a preference for birches (Betula spp.). This choice may facilitate the marking and/or detection of chemical signals and, therefore, the effectiveness of intraspecific communication. Conversely, the abundance of rub trees along footpaths did not seem to depend on the density of bear observations or their relative position within the population center or its border. Our results suggest that Cantabrian brown bears select trees based on their individual characteristics and their location, with no influence of characteristics of the bear population itself. Our findings can be used to locate target trees that could help in population monitoring.

Carrion production is one of the most crucial yet neglected and understudied processes in food webs and ecosystems. In this study, we performed a large-scale estimation of the maximum potential production and spatial distribution of ungulate carrion biomass from five major sources in peninsular Spain, both anthropogenic (livestock, big game hunting, roadkills) and natural (predation, natural mortality). Using standardised ungulate carrion biomass (kg/year/100km 2 ) estimates, we evaluated the relationship between ungulate carrion production and two ecosystem-level factors: global human modification (GHM) and primary productivity (NDVI). We found that anthropogenic carrion sources supplied c. 60 times more ungulate carrion biomass than natural sources (mean = 90,172 vs. 1,533 kg/year/100km 2 , respectively). Within anthropogenic carrion sources, livestock was by far the major carrion provider (91.1% of the annual production), followed by big game hunting (7.86%) and roadkills (0.05%). Within natural carrion sources, predation of ungulates provided more carrion (0.81%) than natural mortality (0.13%). Likewise, we found that the spatial distribution of carrion differed among carrion sources, with anthropogenic carrion being more aggregated in space than natural carrion. Our models showed that GHM was positively related to carrion production from livestock and roadkills, and that wild ungulate carrion supplied by natural sources and big game hunting was more frequently generated in more productive areas (higher NDVI). These findings indicate a disconnection between the main ungulate carrion source (livestock) and primary productivity. Ongoing socio-economic changes in developed countries (e.g. increase of intensive livestock husbandry and rewilding processes) could lead to additional alteration of carrion production processes, with potential negative impacts at the community and ecosystem levels. Overall, we highlight that carrion biomass quantification should be considered a crucial tool in evaluating ecosystem health and delineating efficient ecosystem management guidelines in the Anthropocene.

The rather limited human ability to understand animal vision and visual signalling has frequently clouded our expectations concerning the visual abilities of other animals. But there are multiple reasons to suspect that visual signalling is more widely employed by animals than previously thought. Because visibility of visual marks depends on the background in which they are seen, species spending most of their time living in dark conditions (e.g., in forests and/or having crepuscular and nocturnal habits) may rely on bright signals to enhance visual display. Here, as a result of experimental manipulations, we present, for the first time ever, evidence supporting the use of a new channel of intraspecific communication by a mammal species, i.e., brown bear Ursus arctos adult males relying on visual marks during mating. Bear reactions to our manipulation suggest that visual signalling could represent a widely overlooked mechanism in mammal communication, which may be more broadly employed than was previously thought.

Many animal species use scent marks such as feces, urine, and glandular secretions to find mates, advertise their reproductive status, and defend an exclusive territory. Scent marking may be particularly important during dispersal, when individuals emigrate from their natal territory searching for mates and a new territory to settle and reproduce. In this study, we investigated the scent-marking behavior of 30 dispersing female meerkats (Suricata suricatta) during the three consecutive stages of dispersal—emigration, transience, and settlement. We expected marking patterns to differ between dispersal stages, depending on social circumstances such as presence of unrelated mates and social status of the individuals within each dispersing coalition and also to be influenced by water and food availability. We showed that defecation probability increased with group size during the settlement stage, when newly formed groups are expected to signal their presence to other resident groups. Urination probability was higher in subordinate than in dominant individuals during each of the three dispersal stages and it decreased overall as the dispersal process progressed. Urine may, thus, be linked to advertisement of the social status within a coalition. Anal marking probability did not change across dispersal stages but increased with the presence of unrelated males and was higher in dominants than in subordinates. We did not detect any effect of rain or foraging success on defecation and urination probability. Our results suggest that feces, urine, and anal markings serve different communication purposes (e.g., within and between-group communication) during the dispersal process.