Fencing amplifies individual differences in movement with implications on survival for two migratory ungulates

Fences have recently been recognized as one of the most prominent linear infrastructures on earth. As animals traverse fenced landscapes, they adjust movement behaviors to optimize resource access while minimizing energetic costs of coping with fences. Examining individual responses is key for connecting localized fence effects with population dynamics.

We investigated the multi-scale effects of fencing on animal movements, space use, and survival of 61 pronghorn and 96 mule deer on a gradient of fence density in Wyoming, USA.  

Taking advantage of the recently developed Barrier Behavior Analysis, we classified individual movement responses upon encountering fences (i.e. barrier behaviors). We adopted the reaction norm framework to jointly quantify individual plasticity and behavioral types of barrier behaviors, as well as behavior syndromes between barrier behaviors and animal space use. We also assessed whether barrier behaviors affect individual survival.  

Our results highlighted a high level individual plasticity encompassing differences in the degree and the direction of barrier behaviors for both pronghorn and mule deer. Additionally, these individual differences were greater at higher fence densities. For mule deer, fence density determined the correlation between barrier behaviors and space use, and was negatively associated with individual survival. Yet, these relationships were not statistically significant for pronghorn.  

By integrating approaches from movement ecology and behavioral ecology with the emerging field of fence ecology, this study provides new evidence that an extraordinarily widespread linear infrastructure uniquely impacts animals at the individual level. Managing landscape for lower fence densities may help prevent irreversible behavioral shifts for wide-ranging animals in fenced landscapes.