The interaction between cortisol and testosterone predicts leadership within rock hyrax social groups.

Group movement leadership is associated with higher risks for those in the front. Leaders are the first to explore new areas and may be exposed to predation. Individual differences in risk-taking behavior may be related to hormonal differences. In challenging circumstances, such as risk-taking leadership that may pose a cost to the leader, cortisol is secreted both to increase the likelihood of survival by restoring homeostasis, and to mediate cooperative behavior. Testosterone too has a well-established role in risk-taking behavior, and the dual-hormone hypothesis posits that the interaction of testosterone and cortisol can predict social behavior. Based on the dual-hormone hypothesis, we investigated here whether the interaction between testosterone and cortisol can predict risk-taking leadership behavior in wild rock hyraxes (Procavia capensis). We used proximity loggers, observations, and playback trials to characterize hyrax leaders in three different leadership contexts that varied in their risk levels. In support of the dual-hormone hypothesis, we found that cortisol and testosterone interactions predict leadership that involves risk. Across different circumstances that involved low or high levels of risk, testosterone was positively related to leadership, but only in individuals (both males and females) with low levels of cortisol. We also found an interaction between these hormone levels and age at the low-risk scenarios. We suggest that the close social interactions and affiliative behavior among hyrax females within small egalitarian groups may make female leadership less risky, and therefore less stressful, and allow female leaders to influence group activities.

High-resolution tracking of hyrax social interactions highlights nighttime drivers of animal sociality.

Network structure is a key driver of animal fitness, pathogen transmission, information spread, and population demographics in the wild. Although a considerable body of research applied network analysis to animal societies, only little effort has been devoted to separate daytime and nighttime sociality and explicitly test working hypotheses on social structures emerging at night. Here, we investigated the nighttime sociality of a wild population of rock hyraxes (Procavia capensis) and its relation to daytime social structure. We recorded nearly 15,000 encounters over 27 consecutive days and nights using proximity loggers. Overall, we show that hyraxes are more selective of their social affiliates at night compared to daytime. We also show that hyraxes maintain their overall network topology while reallocating the weights of social relationships at the daily and monthly scales, which could help hyraxes maintain their social structure over long periods while adapting to local constraints and generate complex social dynamics. These results suggest that complex network dynamics can be a by-product of simple daily social tactics and do not require high cognitive abilities. Our work sheds light on the function of nighttime social interactions in diurnal social species.

Sex-associated and context-dependent leadership in the rock hyrax.

In many mammalian species, both sexes may take leadership role, but different traits may play a role in determining variation within species. Here we examine the effect of sex on leadership. We present three complementary datasets derived from a well-studied population of wild rock hyrax (Procavia capensis). The findings demonstrated that male and female rock hyraxes take on different leadership positions, depending on the context. When risk is moderate, more likely to lead are younger resident males, which experience high cortisol and lower testosterone levels. However, during acute predation scenarios, more likely to lead are males with lower centrality status. We suggest that hyrax males exhibit risky behaviors that may reflect their need for self-advertisement. In contrast, leadership among group females is more equally distributed. Females have little to gain from risky actions due to the lack of competition among them, but nonetheless take leadership positions.

Hamsters in the city: A study on the behaviour of a population of common hamsters (Cricetus cricetus) in urban environment.

Animals in urban environments face challenging situations and have to cope with human activities. This study investigated the ecology and behaviour of a population of European hamsters (Cricetus cricetus) living in the city centre of Vienna (Austria). We recorded the surface activities of 35 hamsters in May 2015. Each focal animal was observed for 15 minutes, and a total of 66 focal samples were analysable. As a prey species in an environment teeming with human activities, we predicted a high level of vigilance by the hamsters. The results show that while animals dedicated a lot of time to vigilance, most of their time was spent foraging. The study also explores whether the frequency of vigilance behaviours differ between males and females. We found that vigilance behaviours were expressed in a different manner by males and females. Finally, we investigated the distribution of the burrows on green spaces depending on proximity to trees and on noise levels. We found a biased distribution of burrows, with a spatial preference for location protected by the vegetation and distant to noise sources. Although burrows were located preferentially under vegetation cover, levels of noise did not determine their positions. Moreover, this species does not respond to disturbances like daily urban noises, probably due to habituation. The common hamster is an endangered species; our results lead to a greater knowledge of its behaviour in a persistent urban population.