Certain aspects of social life, such as engaging in intergroup conflicts, as well as challenges posed by the physical environment, may facilitate the evolution of quantity discrimination. In lack of excessive comparative data, one can only hypothesize about its evolutionary origins, but human-raised wolves performed well when they had to choose the larger of two sets of 1–4 food items that had been sequentially placed into two opaque cans. Since in such paradigms, the animals never see the entire content of either can, their decisions are thought to rely on mental representation of the two quantities rather than on some perceptual factors such as the overall volume or surface area of the two amounts. By equaling the time that it takes to enter each quantity into the cans or the number of items entered, one can further rule out the possibility that animals simply choose based on the amount of time needed to present the two quantities. While the wolves performed well even in such a control condition, dogs failed to choose the larger one of two invisible quantities in another study using a similar paradigm. Because this disparity could be explained by procedural differences, in the current study, we set out to test dogs that were raised and kept identically as the previously tested wolves using the same set-up and procedure. Our results confirm the former finding that dogs, in comparison to wolves, have inferior skills to represent quantities mentally. This seems to be in line with Frank’s (1980) hypothesis suggesting that domestication altered the information processing of dogs. However, as discussed, also alternative explanations may exist.

Vocal communication networks can be linked to social behaviour, allowing a deeper understanding of social relationships among individuals. For this purpose, the description of vocal dyads is fundamental. In group-living species, this identification is based on behavioural indicators which require a high level of reactivity during social interactions. In the present study, we alternatively established a proximity-based approach to investigate whether sex-specific differences in vocal communication reflect social behaviour in a species with rather loose social associations and low levels of reactivity: the Southern white rhinoceros (Ceratotherium simum simum). We performed audio- and video recordings of 30 captive animals from seven groups. Vocal networks for the four most common call types were constructed by considering conspecifics at close distance (≤ 1 body length) to the sender as potential receivers. The analysis of the resulting unidirectional structures showed that not only the sex of the sender but also the sex of the potential receiver, the quality of social interactions (affiliative or agonistic) as well as association strength predict the intensity of vocal interactions between group members. Thus, a proximity-based approach can be used to construct vocal networks providing information about the social relationships of conspecifics—even in species with loose social associations where behavioural indicators are limited.

No abstract

Progesterone and oestrogen are the main gonadal steroid hormones that regulate the ovarian activity and induce the fertile oestrus period in females. The monitoring of this receptive phase is particularly decisive for captive breeding and is commonly based on the observation of female behavioural patterns that coincide with their hormonal oestrus. However, in the white rhinoceros (WR), a species that is well known for its impaired reproductive rate in captivity, the female behavioural and vocal indicators of receptivity have not been systematically investigated or linked to their hormonal states so far. In order to close this gap, we combined behavioural and acoustic recordings, conducted over an average period of 32 days, with the analysis of faecal progesterone and oestrogen metabolite concentrations (fPM and fEM) in 27 adult Southern white rhinoceros (Ceratotherium simum simum; SWR) females from 10 European zoos. For eight of the study females, we were able to detect a receptive period indicated by their acceptance of sexual behaviour from the bulls. The comparison of behaviour and vocalization between receptive and non-receptive periods in these females demonstrated that particularly presenting and marking behaviour distinctly peaked during the receptive period, indicating the significance of olfactory signalling for female reproductive behaviour. Based on the analysis of fPM profiles, we were able to identify different reproductive states (cycling, non-cycling, pregnant) in 21 of 27 study females. In contrast, fEM profiles proved to be unsuitable for the detection of ovarian activity. For the majority (five of six females for which behavioural receptivity and endocrine cyclicity were determined), a coincidence of their receptive period and the hormonal oestrus, indicated by a nadir in fPM levels, could be detected. Conclusively, this study revealed a comprehensive behavioural repertoire that reflects the hormonal oestrus in SWR females and can therefore be reliably used for non-invasive ex situ reproduction monitoring.