Quantifying animal social behaviour with ecological field methods

Field studies of social behaviour are challenging due to the need to
record or infer interactions between multiple individuals, often under
suboptimal environmental conditions or with potential disturbance by
observers. Due to the limited field techniques available, we present a
novel method to quantify social behaviours in the field by comparing the
counts of individuals caught in traps across multiple locations sampled
simultaneously. The distribution of individuals between traps gives the
extent of aggregation, and phenotypic data allow for inference of
non-random assortment. As a case study, we applied this method to
populations of three-spined sticklebacks (Gasterosteus aculeatus) in
freshwater ponds, using minnow traps. As expected, we observed a strong
trend for aggregation. We were able to describe the ecological drivers of
aggregation, comparing environmental and phenotypic conditions across
sites. Aggregation was not related to environmental parameters, but was
negatively associated with the proportion of breeding males caught during
the breeding season. No evidence for phenotypic assortment based on body
size was found. These results demonstrate that widely-available ecological
equipment can address questions related to social behaviour. This
cost-effective approach, avoiding the tagging of individuals and
minimising extended observer disturbance, can be applied across various
habitats and species.