Behavioural syndromes going wild: individual risk-taking behaviours of free-ranging wild boar

Behavioural syndromes theory predicts animals will exhibit sets of correlated risk-taking behaviours, with individuals displaying a constant willingness to take risks across different situations. Because this phenomenon has mostly been investigated under artificial experimental conditions, we aimed to establish whether wild animals spontaneously exhibit correlated risk-taking behaviours. We merged a large data set of spatial positions from 43 wild boar, Sus scrofa, with the spatial distribution of risks, modelling their risk-induced resource selection. Elaborating these data by means of a resource selection analysis (step selection functions) and focusing only on periods when individuals were active represents an innovative approach to the study of spontaneous risk-taking behaviour exhibited across different situations. We sampled wild boar from two populations in southern Europe living in extremely different environmental conditions (mountainous versus Mediterranean area). We used model coefficients and parameters as quantitative measures of four different risk-taking behaviours (human avoidance, site fidelity, selection for covered habitat and mobility), for both the population and the individual level. A risk-taking syndrome was detected within both populations, with wild boar clustering in two groups sharing homogeneous sets of risk-taking behaviours. Contrary to the theoretical expectation which predicted individual use of consistent strategies, we observed a compensation among pairs of risk-taking behaviours, with individuals that could be considered risk avoiders on account of strong site fidelity and human avoidance being risk prone in terms of a low selection for covered habitats and a high mobility. Our results suggest that wild animals may adaptively exhibit strategies trading off different risk-taking behaviours. The similarities of risk-taking strategies in the two monitored populations suggested that the observed syndrome was not shaped by biotic or abiotic factors, but rather unintentionally caused by humans.