Speed in the prairies: The Pronghorn
The pronghorn (Antilocapra Americana), a grassland specialist and the lone surviving member of the family Antilocapridae. This species illustrates the harsh, unforgiving predator prey dynamic of the open plains, the extinct American cheetah was presumably the main predator of the Pronghorn reaching speeds of 70 mph. These pressures produced a highly social, short lived, and large brained animal, contributing to there adaptability and learning capabilities. Both sexes travel together, covering extraordinary distances avoiding harsh winter conditions and the frequent grass fires. The high fecundity of the pronghorn compared to other ungulates (twins are the norm) allow for substantial increases in populations following die-offs caused by natural forces (drought, fire, winter), for the preceding 10,000 years the main predator of pronghorns has been that of wolves, and Coyotes, the superior running abilities of mature pronghorns (top recorded speed 85 km/hr) enables them to easily outrun any predator, for this reason they are particularly susceptible as fawns, once they reach six to eight months of age coyotes and wolves no longer poses any threat in a natural environment. Current population estimates in Canada are between 38,000 – 40,000, one hundred percent of these animals are found within southern Saskatchewan and Alberta, the last known pronghorn that resided in Manitoba died in 1881. In the early 1900s extinction was looming for this extraordinary animal, fiercely focused conservation efforts in both the United States and Canada resulted in populations recovering to current levels. It is estimated that populations ranged between 13-30 million before plummeting to 13,000 during European settlement. One can only image what these herds might have looked like as they charged across the grasslands accompanied by millions of bison and wild horses.
“The pronghorn is one of the most beautiful animals I ever saw….The legs are remarkably light and beautifully formed, and as it bounds over the plain, it seems scarcely to touch the ground, so exceedingly light and agile are its motions. This animal…inhabits the western prairies of North America exclusively.”
- John Kirk Townsend May 15, 1834
“When i beheld the rapidity of their flight along ridge before me it appeared reather the rapid flight of birds then the motion of quadruped"
- Mariwether Lewis
Pronghorns were driven to critically low population levels during agricultural settlement in the West. Extensive conversion of native grasslands into crop production, market hunting, and grazing pastures early in the 19th century severely reduced the availability of productive habitat. Fences were erected and used to contain livestock, pushing pronghorn herds to travel alternate and less productive routes. Evolving on the grasslands, pronghorns seldom encountered circumstances where the ability to jump was required, this resulted in no selective pressure for jumping ability in pronghorn evolution, becoming a maladaptation in our modern world. Pronghorns tend to be the species most affected by erected fences within the grassland ecosystem. Restricted movement across the landscape, and removal of native grassland is and continues to be a cause of struggling pronghorn populations.
"The Sublette pronghorn herd, which summers in Grand Teton National Park but still migrates over 200 miles south, near Green River, Wyoming, in winter. This inclination to migrate before severe winter storms was adaptive in the wild, but coupled with there inability to jump obstacles ultimately would produce tragic die-offs in the late 19th century, when legendary winters in the 1880s sent pronghorns southward by the thousands into a new era of barbed-wire strung across the plain”
- Dan Flores, American Serengeti
When we examine species in the Canadian grasslands we discover that migration is traditionally an import component of their ecology. Harsh winters provide little food for wildlife in northern ranges. Winter ranges dictate caring capacities of resident wildlife populations and availability of winter feed is one of the limiting factors for population growth and one of the principal concerns when looking at pronghorn management. Wintering grounds for pronghorn includes habitat consisting of Sagebrush, juniper, and various other forbes and shrubs found in the grasslands, this habitat is crucial for pronghorn survival and concentrated efforts should be put in place to safeguard this habitat in areas where it remains. The primary conservation goals for pronghorn should be increasing winter habitat, and then ensuring connection to this habitat and summer ranges.
Fences are by far the greatest barrier, impeding movement between traditional ranges, cutting of water supplies, and blocking traditional migration routes. Both cattle and sheep fences provide difficulty for pronghorn, sheep fencing tends to be a highly difficult obstacle as it restricts movement underneath, confining pronghorn to smaller and smaller ranges. although large numbers of pronghorn are entangled in fences each year, this pales in comparison to pronghorn deaths due to malnutrition, caused by decreased access into high yield forage areas. In 1964-65 near the area of Marfa Flats large die-offs in winter where caused by the inability for pronghorn to leave the area, this resulted in losses as high as 90 percent. Solutions Like increasing the height of the lowest fence wire to 18” will allow sufficient room for pronghorn to squeeze underneath, this bottom wire should also be round and contain no barbs (This is critical as removal of hair from the backs of pronghorn has been noted to affect winter survival rates in northern populations), This method is the easiest to implement but understanding that cattle calves of smaller size may go under and have difficulty returning under the fence is occasionally a concern. Popowski and Pyle sum up the position by saying” fences are as foreign to the pronghorn as meat is to a vegetarian”. Highways and rail lines will cause significant distress and can severely limit movement, One doe in Alberta spent 10 days trying to cross the Trans-Canada Highway, this issue is one that both wildlife managers and insurance agencies need to focus on as roads become busier. Additionally, habitat availability is a growing concern, if sagebrush habitat continues to decline then so will the pronghorn reliant on that feed, determining the carrying capacities of existing habitat along with mapping out what areas can be used to increase habitat is a priority for pronghorn management. Identifying grassland habitat is critical so remaining ranges can be connected instead of fragmented, this involves the co-operation of landowners, communities, industry, and agencies. When identifying proper habitat we must look for areas that provide favorable opportunities for pronghorn, in general pronghorn require a minimum of 25-30 square miles of continuous grassland. The ground ideally has low relief with few major obstacles such as rivers, lakes, and tall grass prairies (vegetation over 10” will become a barrier to movement and feeding). These parcels of habitat should not be long narrow islands of habitat that extend into cultivated areas. on the other hand, cultivated land checker-boarded by native grassland is often suitable for small populations. The impact of weather can be sever in certain circumstances but often is not the major problem, however, when looking at snowfall levels, events that exceed 15cm of snow depth, specially for extended periods of time can cause considerable problems.
Q: But one might ask, if there are more pronghorn on the landscape doesn’t that mean less feed for cattle? This question is one that is important to fully understand. As pronghorn evolved alongside bison they developed a strong mutualistic relationship. As bison moved across the grasslands clipping nutrient dense grasses and ignoring often-posinous species of sagebrush, locoweed, rabbitbrush allowed forbes and shrubs to grow in there wake. pronghorn followed these mighty herds of bison clipping and removing large quantities of shrubs and forbes allowing grasses to re-establish there dominance, this cycle is one of mutual benefits, and one that modern ranches and livestock operators can apply.
The challenges that lie ahead are that of cooperative management, economics, personal, and ecological values, it will invariably remain a difficult balancing act as interests are oftentimes not aligned. However, as we learn more about what critical habitat is required, migration routes, and barriers causing distress, we can improve management practices and regulations to reflect those changes. In the end, working collaboratively is the main goal, values must be shared if populations are to increase, we similarly need to understand that, as with all government programs and conservation initiatives where public money is being invested, the opinions of those citizens involved are vital for success. What needs to occur on a larger scale is an inventory of remaining critical wintering grounds and high yield grassland, once an inventory is established then managers can develop plans around that critical habitat, once we understand what we have left, we can then start moving towards a holistic management approach. Although, it may never be possible to return the grasslands to there original glory we can never less try our best for the generations to come, to witness something so magnificent as generations before us did.
“As far as we could see, there were antelope and mustangs grazing in the waving sea of the grass” the whole tableau “rendered misty and unreal by the mirage that hovered over the plains”
-George Wolfforth, 1884