Social behaviour in stallion groups (Equus przewalskii and Equus caballus) kept under natural and domestic conditions

Abstract

The aim of this study was to investigate social behaviour in differently reared stallions in their respective environments; one group of stallions was reared under typical domestic conditions whereas the other group was reared and lives under natural conditions. The domestic group consisted of 19, 2-year-old stallions (Equus caballus), which were all weaned at 4 months of age and experienced either individual or group housing facilities before being pastured with the other similarly aged stallions. The natural living and mixed age group of Przewalski stallions (E. przewalskii) consisted of 13 stallions, most of which were juveniles (n=11, ≤4 years; n=2, >9 years). The domestic group was studied in a 4-ha enclosure at the Danish Institute of Agricultural Sciences and the Przewalski group under free-ranging conditions in a 75-ha enclosure in the Askania Nova Biosphere Reserve, Ukraine. Behavioural data was collected during 168 h of direct observation. The occurrence of 14 types of social interactions was recorded and group spacing behaviour was studied using nearest neighbour recordings. In spite of very different environments, reflecting domestic and natural rearing conditions, many similarities in behaviour was found. Play and play fight behaviour was very similar in the two stallion groups. Quantitative differences were found in social grooming since Przewalski stallions groomed more frequently (P=0.004), and in investigative behaviours, since domestic stallions showed more nasal (P=0.005) and body sniffing (P<0.001), whereas Przewalski stallions directed more sniffing towards the genital region (P<0.001). These differences may, however, be attributed to environmental factors and in the period of time the stallions were together prior to the study period. Quantitative differences appeared in some agonistic behaviours (kick threat, P<0.001; and kick, P<0.001), but data do not support earlier findings of Przewalski horses being significantly more aggressive than domestic horses. In general, Przewalski stallions engaged in more social interactions, and they showed less group spacing, i.e. maintained a significantly shorter distance between neighbours (P<0.001). The study indicates that also domestic horses, which have been reared under typical domestic conditions and allowed a period on pasture, show social behaviour, which is very similar to that shown by their non-domestic relatives.

Introduction

Animals living under natural conditions are regarded as showing the normal behaviour of that species, and deviations from normal behaviour in domestic animals may relate to changes resulting from domestication, or they may be caused by environmental factors. Price (1984) defined domestication as ‘that process by which a population of animals becomes adapted to man and to the captive environment by some combination of genetic changes occurring over generations and environmentally induced developmental events reoccurring during each generation’. Domestic animals generally show reduced responsiveness to environmental changes, which may not only be expressed in their reaction towards humans, but also in intra-specific reactions and investigative behaviours. Domestication may additionally induce a change in group spacing behaviour since management practices, which minimise competition for resources, should permit captive populations to exist at relatively high densities (Price, 1984).

Studies of feral horses living under natural conditions indicate that the species-specific behaviour of equids has remained relatively unaffected by the domestication process (Tyler, 1972, Feist and McCullough, 1976, Waring, 1983), and thus domestication seems to have influenced the quantitative rather than the qualitative nature of social behaviour in horses. Quantitative changes may include a reduction in aggressive behaviour because the domestic environment reduces the selective advantages of aggressive potential in securing resources.

Direct comparisons of social behaviour in domestic and non-domestic horses are lacking in the literature, and are made difficult by the fact that domestic horses are kept under conditions, which are very different to the natural environment. Typical rearing conditions for domestic horses include early weaning of foals, commonly at the age of 5–6 months, after which they may experience either individual housing conditions or enter groups with other similarly aged horses. In sharp contrast to these conditions, studies on horses in natural environments show that horses tend to live in mixed age groups and stay with their natal herd till approximately 2 years of age (for a review see Waring, 1983). The rearing environment and the environment in which an animal lives is likely to affect the behaviour of the individual. For instance, it has been shown that social restrictions affect the behaviour of horses (Christensen et al., 2002), and rearing animals in physical isolation from older, socially dominating conspecifics may preclude the development of normal adult-like behaviour patterns of agonistic behaviours and may result in the retention of juvenile social behaviours (Price, 1984).

Feh (1988) and Keiper and Receveur (1992) reported more aggressive behaviour in groups of Przewalski horses, which is the closest wild relative of domestic horses, than in feral horse groups. However, these findings were based upon a limited number of stallions (three Przewalski stallions versus eight Camargue stallions by Feh, 1988), or upon comparisons between different studies (Keiper and Receveur, 1992). The present study aims to extend these earlier investigations by studying social behaviour in Przewalski and domestic stallions within the same study, with a large number of stallions per group, and using the same observational techniques and observers on both groups.

Investigations on behavioural differences between domestic horses and their wild relatives—displayed in their respective home environments—are of great importance in understanding the span of equid behaviour. The present study investigates and discusses social and group spacing behaviour in domestic stallions and in non-domestic Przewalski stallions, reared under typical domestic and natural conditions, respectively.