Lutra 60(1)_Linnartz & Linnartz-Nieuwdorp_2017

The social organisation of natural herds of koniks (Equus caballus): subordinate stallions, rule or exception?

This article describes the social organisation of herds of free-roaming koniks in the Netherlands and elsewhere in Europe, with a particular focus on the Oostvaardersplassen. Attention is directed to: 1. Herd size in relation to habitat conditions. 2. Composition of harems within those herds. 3. The role and relative number of subordinate stallions in those harems. On the basis of this information, the article subsequently describes the assumed situation regarding subordinate stallions at the Oostvaardersplassen and in other areas with large herds of free-roaming horses. Following this, the validity of this assumption is investigated for other konik grazing areas within the Netherlands, using field data that also include those from a repeated study about the Oostvaardersplassen. Finally, it is investigated whether the outcome also applies to feral horses (Equus caballus), Przewalski’s horses (Equus przewalskii), zebras and African and Asiatic wild asses (Equus spp.) elsewhere in the world. The freeroaming koniks in Europe, in contrast to those elsewhere in the world, mostly live in nature areas that are rich in food and have an ample drinking water supply. In such areas, koniks appear to prefer to live in large groups. The ample food supply in the areas studied supports such large herds. In two other areas that were less rich in food, the harems opted to live separately. Large herds were also often found to break up into smaller herds in the wintertime, when food would become scarce. Exclusive home ranges with only one harem were found in certain areas with narrow road crossings or traversable dykes, or in long and narrow areas. Exclusive home ranges are different from true territories, as only the harems were defended, rather than the land itself. Thus, independent harems or groups can be formed not only as a result of food scarcity but also because of the type of terrain. Free-roaming koniks, in Europe, live in herds with a social organisation of harems and bachelor groups that is similar to elsewhere in the world among wild Equidae and feral horses. In Europe, however, this organisation can only be observed in nature areas with larger herds that live in an autonomously chosen social structure - thus, in areas with only limited human intervention. The presence of multiple harems, however, does mean that dominant stallions continually need to fend off the competition. This is why harems in such large herds often have a particular composition in which subordinate stallions also play an important role, in addition to the dominant stallion, both in tasks and numbers. Having subordinate stallions around offers advantages; they help to defend the harem and, thus, contribute to achieving the much-needed peace and quiet for mares and their foals. Subordinate stallions also help to prevent predation, and larger numbers of subordinate stallions are seen in situations of increased risk of predation.
Subordinate stallions themselves, however, experience only few advantages in relation to their efforts. Thus, among the free-roaming koniks studied, there appeared to be no mutualism or altruism. Subordinate stallions and dominant stallions do appear to have different temperaments. Predation also seems to lead to the formation of large groups as well as to increased collaboration between stallions, although this is not - yet - the case in the Dutch situation. The occurrence of subordinate stallions, therefore, is the rule rather than the exception, and appears to be related to herd size, the presence of rivalling stallions, predation and food supply.