Data from: Spatial strategies in non-territorial societies: How feral horses maintain boundaries with other groups

Encounters between competitive individuals or groups are common in social
animals and can involve costly aggression; thus, animals often employ
strategies to minimise direct conflict. However, research on whether and
how animals adjust their group spatial structure when they encounter or
spatially co-occur with a different group remains limited. We investigated
how non-territorial units in feral horse multilevel societies manage
spatial encounters with neighbouring units. We observed 25 reproductive
units in northern Portugal, using drones, and employed statistical
analyses to quantify spatial dynamics. We found that horses actively
adjusted their spatial formations depending on the proximity of other
units. Units became more circular and cohesive when other units
approached, but when extremely close, they elongated their shapes to avoid
boundary crossings. These adjustments indicate that horses maintain
flexible unit boundaries to prevent mixing with other units. A notable
exception was a particular pair of units that frequently crossed
boundaries and intermixed, representing a unique social level within the
horse multilevel society. Overall, our findings indicate that feral horses
respond adaptively to inter-unit encounters by balancing the benefits of
aggregation with the need to reduce direct overlap, providing new insights
into the spatial organisation of non-territorial societies.