Temporal stability of social structure and behavioural synchronization in Shetland pony mares (Equus caballus) kept on pasture

Abstract

The temporal stability of synchronization was studied for two consecutive years in a herd of 10 Shetland pony mares kept on pasture. Direct field observations lasted 1.5–2.5 h per session between 8:00 am and 8:00 pm, adding up to an observation time of 74 h in the first and 134 h in the second year. Behaviour, nearest neighbour identity and distance were recorded individually every 15 min by point sampling. Rank order remained very stable between years (τb = 0.91; P < 0.01). All mares showed preferences for the proximity of primarily one specific group member. K-coefficients of synchronization, i.e. non-random synchronization, were higher in the second year of observation (2010: κ = 0.22; 2011: κ = 0.54; t = 2.69; P = 0.007). Among the different parameters evaluated, the Kappa coefficient proved to be most reliable for assessment of synchronization at the group level, because it is not inherently affected by time budgets. A high degree of behavioural synchronization might be the basis of stable group cohesion. Preferences between individuals should be considered for re-groupings in managed horse groups.