Fences, roadways, and wildlife
New science on the effects of roads and fences on pronghorn migration
So much of the environmental news these days concerns climate change that it is easy to forget that humans affect the world in a multitude of other ways, from the ubiquitousness of light pollution to plastics accumulating in our rivers, forests, oceans, and even our bodies.
Some of the ways in which humans have altered our environment is by building fences and roadways. We have roads on every continent, even Antarctica. And humans have built fences for about as long as we’ve been human. If you laid out all the fences in the world they would exceed the total length of all the roadways—all the two-lanes, all the freeways, and all the parkways—several times over. And we continue to add more and more fences all the time.
There has been a fair amount of science on the effects that roadways have on wildlife. What the science has found is that roads mess everything up. As anyone who has stepped from a yard into a street knows, roads affect the surrounding temperature. They also affect soil density and water content. Roads increase ambient dust. They increase runoff during rainstorms. Roads bring heavy metals and salts to an environment. When people build roads, there is more hunting. More nonnative and invasive species enter the environment, too, once a road is built.
Roads break up habitat of wildlife and can further affect their behavior. Last year researchers found that a gravel paved roadway in the Negev Desert, in Israel, disrupted the vegetation of the desert, with higher shrub coverage on the upland side of the roadway. Subsequently, the populations of insects differed on either side of the road.
Loudon Wainwright will tell you that some animals aren’t so lucky crossing roads
Compared to roads, a country fence can seem benign, but they affect the behavior of wildlife. Larger animals, when confronted with a fence in their path will “patrol” the fence, looking for ways to go under or around the fence. Some animals deflect away, or “bounce” back the way they came. They sometimes go back and forth along a short portion of the fence. Animals get trapped sometimes, when they go into a more enclosed area of fencing. Worse yet, animals sometimes get stuck in fences and die, with young being particularly susceptible.
Scientists have examined the effects of roads and of fences, but until recently, no research has been done on what effect these structures may have on wildlife in tandem. In work published at the end of last month, August, scientists in Canada looked at the effects of roads and fences on the behaviors of native pronghorns, large, semi-migratory antelope native to Canada, the western U.S. and Mexico. The paper was published in the journal Movement Ecology
.Unsurprisingly, the antelopes avoided fences and roadways. When fences accompanied roads, particularly when roads were fenced on both sides, the migrating pronghorns tended to “pile up” in close proximity to the fences. The scientists surmise that, like humans, the pronghorns accumulated on one side of a fence while they sought out a way to get across the triple barrier.
Pronghorns live in Canada, the western United States, south into Mexico. They feed on grasses, herbs, and sagebrush, and prefer to roam deserts, grasslands, and shrub biomes, such as coastal sage scrub, and chaparral. Pronghorns stand about two and a half to three and a half feet tall and can be almost five feet from nose to tail. Black antlers adorn adult males, giving the appearance of a headdress. Biologists estimate that historically the North American population of pronghorns may have been as high as 35 million. They number now in the tens of thousands. Though their numbers are but a fraction of what once was, they are not considered vulnerable to extinction and are a game species.
The research of this study goes back a ways, back to 2003 through 2007. The research team captured and fit dozens of female pronghorns with a tracking collar that stayed with the animal for a year before automatically dropping off (and which was collected in the field later). They tracked the pronghorns in a 23,000 square mile expanse of grassland in southern Alberta, Canada, an area about the size of West Virginia. The landscape is one of big, flat, open plains and rolling hills, and there aren’t a whole lot of people living in the area.
Though initially categorized as three different roadways, based on surface type, number of lanes, and traffic volume, in their final analysis the scientists did not distinguish one roadway from another. With the human population of the area being so low, the roads may not have differed a great deal. Then again, this probably opens up a whole area of study to find out how large animals react to wider roads or busier roads.
The scientists suggest that wildlife needs to have more ability to cross fences and roadways. There have been some very ambitious endeavors to create these habitat connecting features, including one to traverse the multi-lane 101 freeway north of Los Angeles.
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