Across western North America, migratory ungulates like pronghorn and mule deer benefit from being able to travel through protected corridors. Several states, including Wyoming, Colorado, and New Mexico, along with the U.S. federal government, have passed policies aimed at protecting these corridors and ensuring that migratory ungulates have room to roam.
But even with legislative support, the actual design and implementation of corridors in the landscape can remain a complicated challenge.
Merkle, J.A., Lowrey, B., Wallace, C.F., Hall, L.E., Wilde, L., Kauffman, M.J. and Sawyer, H. 2023. Conserving habitat for migratory ungulates: How wide is a migration corridor? Journal of Applied Ecology 60(9): 1763-1770.
Current methods for delineating migratory corridors usually incorporate complex statistical techniques that rely on individuals’ GPS collar data and all its associated uncertainty. The result is often a recommendation for a corridor with variable width, or with excessive width, and which may not even be completely connected, leaving managers to make their own guesses about how to actually implement it.
What if there is a better way? A new perspective suggests that instead of using complex statistics to delineate migratory corridors, why not rely on the ecology and functional requirements of the animals using those corridors. In other words, focus on the practical: create a line that connects successive GPS locations representing an animal path, and then put a fixed buffer around that movement line. That method eliminates the need to account for variables such as how often GPS data points are collected or how non-linear the path is, making it straightforward to conceptualize and use.
Although using a line buffer to create a corridor might seem like an oversimplification, it’s that simplification that makes so useful. The fear is that using such a simple method may lose important information, making the corridor that was created ineffective. But in a test of this method, GPS data from four collared pronghorn and mule deer in Wyoming showed that all of the animals stayed within 200m of the movement line 95% of the time. This suggests that a consistent 400-m wide corridor would likely be effective, and – just as important – does so in an easy and intuitive manner.
While the creation of corridors should always be based on the best available data, sometimes simpler methods can suffice to achieve the same goals as more complex ones. Using a method based on biology and function, rather than one focused on statistics, may lead the focus of wildlife conservation back to the ecology at hand, and also make it more likely to overcome implementation challenges. Then it becomes a win-win situation for both wildlife and the managers tasked with protecting them.
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