One of the most vexing problems in corridor design is: how wide should corridors be? This may be the most frequent question I am asked by land managers who are planning to create or restore corridors. A new and refreshing approach to answer this question has been taken by Stephanie Coster and colleagues in their studies of frogs and salamanders.
The group considered corridors that connect the ponds used by these amphibians for breeding and upland forests that they pass the rest of their years in. To determine the width needed to connect these habitats and to provide safe passage, the group relied on the behaviors of the frogs and salamanders. As they moved away from ponds, what width did their path take? These behaviors could serve as an informed basis for creating corridors of a width that serve the conservation purpose for which they are intended.
The method was straightforward: using radio-telemetry, determine the general linear path of dispersing frogs and salamanders. Then, using that path, draw an arrow from each marked location to the path. Each route taken by an animal was in reality a zigzag around that linear path. The distances from the actual route to the linear path were used to generate a measure of the width of the movement path. For these amphibians, paths were 40-50 m wide. An additional observation with implications for corridor conservation is that the individuals that moved furthest also had the widest paths.
What I liked most about this study was the use of information about the behavior of animals to determine their conservation needs. The approach is direct in connecting animal ecology to conservation action. Another, more historical approach to estimating corridor width has relied on animal home range sizes. This approach complicates matters, as it mixes two potential functions of corridors, as movement pathways and as habitat for corridor-dwellers.
Behavioral approaches to defining corridor length and width such as this one have great promise. But in the end they tell only part of the story. For example, the width of corridors defines where their boundaries are located, and these habitat edges both guide behaviors and provide entry points for antagonistic species, like predators or competitors. And, in many cases, corridors are intended for many species, in which case more information on behaviors will be needed. When considering these different elements, it is hard to escape the conclusion that wider corridors will benefit more animals and plants with fewer costs. Still, behaviors of animals being conserved, such as those observed in this study, will provide strong basis to inform conservation action.