Associative behaviour in Przewalski's horses reintroduced into Mongolia

Abstract

Allogrooming is an important associative behaviour in social mammals that has hygienic and/or social functions and may be mediated by kin selection or reciprocity. Equids exhibit allogrooming and another associative behaviour, stand resting in close proximity. We examined patterns in these behaviours in four harems of Przewalski horses Equus ferus przewalskii, reintroduced into Mongolia to assess whether they were simply reciprocal behaviours that had a hygienic rather than a social function. We conducted 860 hours of observation over 15 months between April 1998 and July 2000. Allogrooming was infrequent (median frequency of 0.02 acts horse-1 × hour-1, n = 363 acts, IQR = 0–0.06), occurring more on the withers (62% of observations) than any other body part. Allogrooming was more frequent in spring and autumn, and morning and evening. There were no significant correlations between relatedness of partners, dominance rank, tenure length, whether individuals changed group, age or aggressive behaviour and the frequency of allogrooming in any harem. Stand resting together was less frequent than allogrooming (median frequency of 0.00 acts horse-1 × hour-1, n = 335, IQR = 0–0.014). In contrast to allogrooming, stand resting together was confined to spring and occurred more during the middle of the day. There were no significant differences between harems, between relatedness and the frequency of stand resting together within any harem, and with age and tenure. In all, we found no evidence of a social function of either allogrooming or stand resting together, but both occurred most frequently at times of the year when they would be needed for coat care or to reduce flies around the face. Our results support our hypothesis that associative behaviours were simply reciprocal hygienic arrangements with no evidence that kin selection was involved, although a social element to the behaviours cannot be completely ruled out.

Keywords

• allogrooming
• Equus ferus przewalskii
• hygiene
• mutual grooming
• reciprocity
• relatedness