Effect of pasture size on behavioural synchronization and spacing in German Blackface ewes (Ovis aries)

• We studied plot size effects on spacing and behavioural synchronization in sheep.
• Distances between ewes were derived from direct observations and aerial photographs.
• The sheep kept small distances on all plot sizes.
• Synchronization was high on all plots, probably resulting from close spatial proximity.
• Aerial photography proved a valuable tool in the analysis of spacing behaviour.

This study aims to assess plot size related changes in spacing and behavioural synchronization in a herd of 14 German Blackface ewes kept on three different pasture sizes: S (126 m2), M (1100 m2), and L (11,200 m2). In direct field observations, behaviour and nearest neighbour distance were recorded individually. Additionally, interindividual and nearest neighbour distances were derived from aerial photographs of the herd taken on plot sizes S and M. Nearest neighbour distances <1 m accounted for more than 60% of observations, and were more frequent on plot size L than on plot sizes S (Z = 3.3; p < 0.01) and M (Z = 3.2; p < 0.01). Average interindividual distances were significantly smaller on S (4.89 ± 2.62 m) than on M plots (5.99 ± 3.06 m; t = 7.3; p < 0.01). Synchronization tended to increase with plot size (K(S) = 0.42; K(M) = 0.52; K(L) = 0.66), but was not accompanied by a concomitant increase in dispersion. Aerial photography proved a valuable tool in the analysis of spacing behaviour as intraindividual repeatability of the derived distances was highly significant (Kendall’s W between 0.32 and 0.58; p < 0.01). The sheep kept small distances on all plot sizes, thus the high degree of behavioural synchronization might be mainly attributed to the motivation for close proximity to any conspecific.