"Freundschaft" bei Huftieren? - Soziopositive Beziehungen zwischen nicht-verwandten artgleichen Herdenmitgliedern

Aims of the study were the demonstration, verification and quantification of friendships in horses, donkeys, sheep and cattle. Further analyses investigated situation-specific aspects, dynamics and duration, asymmetry within the relationships, factors enhancing these bonds, and the benefits of friendship. Ten herds of domestic ungulates (2-3 of each species), comprising 11-60 members (234 animals in total) were studied in the field (SE-England) over two years (approx. 1500 h). Cattle were female, sheep were male; the equids lived in mixed-sex groups (males castrated). Apart from the cattle (heifers), all animals were adult. A comparative, quantitative, objective, systematic and individual-based longitudinal approach was chosen. Study set-up excluded kinship and sexual motivation as an alternative basis for bonds. The observation of spontaneous behaviour was complemented by experiments; different sampling and recording techniques were applied. Frequencies of spatial proximity (two nearest neighbours) and of partner choice for sociopositive interactions (social grooming, resting in physical contact, sharing feed, documenting behaviour s.l.) served as indicators of inter-individual preferences. The complex nearest neighbour analysis required the development of a customised evaluation software (NENESYS). For subsequent statistical analyses mainly multivariate tests were employed (e.g. MDS, Cluster Analysis, Mantel-Test). The concept of friendship was 'borrowed' from human social psychology: This discipline, however, provides neither a consistent definition nor a universally applicable terminology. It was necessary to establish a generally valid, precise definition based on criteria regarding only form and content (not function). Demonstration and verification of friendships proved successful for all four ungulate species. The concept of friendship thus ought to be extended beyond the order of primates. Except for cattle, the demonstration and verification were twofold (distinct preferences for certain neighbours and for specific partners for sociopositive interactions). The quantification revealed both inter- and intraspecific differences. Both extent and strength of the neighbour preferences were greatest in horses, intermediate in sheep, and lowest in cattle. Friendships of donkeys were the least extensive. Their strength, however, was similar to that in horses. Comparing inter-individual preferences across up to four different situations (neighbours when grazing or resting, social grooming, feed sharing), distinct interspecific differences became evident. Situation-specifity was found to be weakest in horses (mostly the same partners in all situations), strongest in donkeys and cattle, and intermediate in sheep. Contrary to the general belief that sheep do not engage in social grooming, two behaviours were identified, which possess at least the psychosocial functions of allo-grooming: horn- or head-rubbing and reciprocal cheek-to-cheek-contact. While the former has been occasionally described and controversially interpreted in the literature (agonistic vs. respectful), cheek-to-cheek-contact was documented for the first time. A classification as sociopositive behaviours is suggested for both. Due to study design, friendships could be traced over a maximum of 18 months. The duration of the bonds among both horses and sheep was comparable to that given in the literature for herds whose social networks were based on a mixture of kinship and friendship; cattle relationships were shorter, those in donkeys were twice as long as had been shown to date. Results indicate that preferences in different situations vary with respect to their frequency between different phases of friendship development. Aspects of asymmetry became particularly evident during unilateral grooming in bovids. Similarity with respect to age (cattle) and possession of horns (sheep) proved to be factors, which encouraged friendships significantly. The popular notion that horses of similar coat colour prefer each other, was not supported. Ungulate friendships do not so much result in direct practical assistance, but rather manifest themselves as psychological benefits in the form of social or emotional support. Emotional support and social grooming reduce psychological and physiological stress. Improving the animals' health, they ultimately have an indirect practical benefit. Animals and their owners alike gain from ungulate friendships (ethical and anthropological motivation for animal welfare): Husbandry systems that accommodate the animals' physical as well as psychosocial needs are prerequisites for healthy and efficient livestock. Results are translated into explicit recommendations immediately and expeditiously applicable to farming practice. A 'Regelkreismodell' integrates the different aspects addressed in the study. Visualising their complex interrelations, it facilitates the generation of precise hypotheses for future research.