A Town of Two Tails: Apologies to Dickens

In the midst of the prairie the taller grass gives way to a small expanse of cropped grass interrupted by numerous dirt mounds. Grazing this neatly trimmed lawn, a herd of buffalo watch our approach unconcerned.  However, looking closely, tiny sentinels raise up on their rear haunches to signal an alarm at our intrusion.  We have just come upon a prairie dog town, the residents of which have seen their best times come and go while their worst of times are upon them. This is the tale of the two most notable tailed-dwellers of the prairie dog town—the prairie dog and the American bison.

Picture from Smithsonian National Zoo & Conservation Biology Institute

                Like the buffalo the prairie dogs blanketed the Great Plains and the surrounding prairies by the hundreds of millions—with some estimates as high as 5 billion—up into the 20th century. Human intervention, though, has decimated the prairie dogs just as it did to the American bison. The conversion of the rich soil of the prairies to the “true religion” of agriculture tore up and turned over these sculptured underground dwellings.  Those who did not die from the apocalyptic loss of their habitat were hunted down and eradicated by farmers and ranchers who saw these rodents as just another destructive varmint. Prairie dog populations have also declined due to bubonic plague—an indirect human intervention—for which they have no natural immunity.  Sylvatic bacterium, the cause of bubonic plague, was brought to the North American continent by rats which sailed the Atlantic along with the European immigrants. Generally, once infected, an entire colony may be lost.  Another keystone species sacrificed to the god of Manifest Destiny.

                Prairie dogs, a seeming weakling, weigh in at about one-and-a-half pounds. Their numbers, however, more than make up for their small mass providing a significant impact to the prairie economy.  Prairie dogs live in colonies consisting of smaller family units called coteries.  The uniqueness of these rodents lies in their engineering ability to build towns. Not really a town, this unique residential area is a system of burrows engineered and excavated by these furry little rodents.  “Build,” then, is perhaps an incorrect term.  Rather they dig, excavating burrows, constructing complex systems containing sleeping quarters, nurseries, food pantries and even a cemetery of sorts.   A single colony may cover thousands of acres [1].

                Their burrows are wonderfully constructed. The genius lies in how the openings are constructed.  There are actually two openings, one at the front and one in the rear, allowing air flow.  The flow of air is regulated by mounding the excavated dirt at the front entrance.  The mound is usually a few inches—though can be as high as two feet–above the entrance.  The wind across the top of the mound is much faster than at the ground-level of the entrance since the friction caused by the ground and the grass slow the wind.  The faster wind speed at the top of the mound draws stagnant air out of the tunnels thus providing a steady flow of fresh air into the soil-level rear entrance [2]. This lowly ground squirrel utilized the wind as a renewable source long before the thought entered our magnificent brains.

Prairie Dog tunnel-housing also serve as a safe space, providing security against most predators. Too small to withstand many predators the prairie dogs use borrows to evade the horror of being dinner.  The openings, which are too small for most predators—such as foxes, coyotes and wolves—provide a convenient escape route.  However, the openings do not restrict other predators such as the prairie rattle snake or ferrets.  In the case of the prairie rattle snake the prairie dogs do not rely on their burrows for protection.  Instead they “gang-up” on the snake.  Since the snake cannot hide in the cropped grass of the prairie dog town, it is easily spotted and surrounded by the residents of the burrows, quickly turning the tables.  The hunter becomes the hunted.  The prairie dogs fling dirt in the snake’s face, by turning their backs on the predator and kicking up dirt with their hind legs.  Others may dart to the snake’s tail, biting harshly into its tail, and then dart away to escape the answering strike [3].

                Ferrets, on the other hand, are not so easily evaded. Since the ferret can easily enter the burrows—and often will seize occupancy—the prairie dog’s only hope is to out run the ferret.  The Black-Footed Ferret is the natural enemy of prairie dogs, depending almost entirely on prairie dogs for its sustenance, constituting 90% of a ferret’s diet.  With almost a 95% loss of the prairie dog’s habitat, the extermination efforts of ranchers and farmers, and introduction of bubonic plague, the prairie dog has become a threatened species, with the dependent ferret becoming an endangered species [4]. 

Black-footed Ferret

These underground architects are key, then, to the survival of other species, not just as prey, but as providers of affordable housing.  Abandoned or otherwise unoccupied burrows become shelter for prairie rattlers, burrowing owls, toads, jack rabbits, and spiders. And, as in the case of ferrets, the burrows are simply taken over.  With the decline of the prairie dogs, these species have subsequently loss habitat. 

Adept engineers these squirrelly diggers are also wise landscapers.  The prairie dogs transform the landscape around their colonies.  The surrounding grass and other plants are kept closely cropped to the ground, both for eating and for providing a clear view of potential predators.  This well-manicured yard also provides habitat for other species—for instance, birds that live in short-grass environs.

                The mounds of dirt and the cropped grass are also invitations to the largest denizens of the prairie—the bison.  Short grass is a bison’s dream diet.  The closer the blade is to the roots  the higher the percentage of protein and the lower the percentage of cellulose.  By grazing the same ground every day prairie dogs keep the grass short, inviting the bison to a culinary delight.  Closely cropped grass is a necessity to a prairie dog, but it is a treat for buffalo. 

                The bison do not just come for the grass, however.  The mounds of dirt are another attraction.  The excavated soil is perfect to fill their hair, which drives out insects and provides a coolant for hot days.  So the little chimneys of dirt erected in prairie dog town are a venerable day-spa of wallowing for the behemoths of the plains. 

A bison wallowing

                The relationship between prairie dogs and bison is not one-sided, though.  Bison also bring something to the table, or rather, leave something behind.  This other keystone species provide re-purposed grass.  That is, grass processed into fertilizer.   The longer the bison hang around the more they spread their contribution, and the greener the grass becomes.  Buffalo chips are gifts that keep on giving [5].

                Finally, bison make prairie dog towns possible.  Everywhere except in the western short-grass regions, prairie dogs depend on bison grazing to provide short enough grass for the prairie dogs to establish residence there.  This ground squirrel will not live in tall grass since it is less nutritious and hides predators [6].

                 The ending of the tale of the town of two tails is still being written.  The recognition of the prairie dog and the American bison as key to the survival of the Great Plains and the prairies has sparked concerted efforts to restore this excavating rodent and the grass-processing behemoth of these ecosystems.  As prairie dog habitat recovers, a return of other species is seen.  Homes become available for the burrowing owl and the prairie rattler.  Meals become available for the black-footed ferret enabling a retreat from extinction.  Bird populations of short-grass environs recover.  Where the buffalo roam and the prairie dog digs, the Great Plains see a renaissance.     

End Notes:

[1]  Boyce, Andy and Andrew Dreelin. Jul 02, 2020. Ecologists Dig Prairie Dogs and So Should You. Smithsonian National Zoo and Conservation Biology Institute. Nationalzoo.si.edu. Retrieved 22 Aug 2020. https://nationalzoo.si.edu/conservation-ecology-center/news/ecologists-dig-prairie-dogs-and-you-should-too .

[2] Lott, Dale F. 2003. American Bison: A Natural History. University of California Press. Berkeley. 127-128.

[3] Lott. 131.

[4] Anderson, Chamois. Nov. 14, 2019. Ferrets and Prairie Dogs and Bison,  Oh My! Defenders.org. Retrieved 30-Aug-2020. https://defenders.org/blog/2019/11/ferrets-and-prairie-dogs-and-bison-oh-my#:~:text=Bison%20often%20prefer%20foraging%20on%20lands%20occupied%20by,birds%20such%20as%20mountain%20plover%20and%20burrowing%20owl.

[5] Lott. 128. See also the posting dated 26 April 2019, “Dung Cakes and Feces Pie: Yum!”  Bisonwitness.com.

[6] Lott. 128.