Black-tailed Prairie Dogs and Their Owls
By: Michael W. Nickell
Meriwether Lewis is said to have coined the terms “barking squirrel” and “prairie dog.” Prairie dogs (Cynomys) were first described in the journals and diaries of those in the Lewis and Clark Expedition (1803-1806). The common name is misleading as they are not related to dogs but are in the squirrel family (Sciuridae) of rodents.
There are five species of prairie dogs indigenous to North America:
Utah Prairie Dog---C. parvidens
Gunnison Prairie Dog---C. gunnisoni
White-tailed Prairie Dog---C. leucurus
Mexican Prairie Dog---C. mexicanus
Black-tailed Prairie Dog---C. ludovicianus
It is the black-tailed prairie dog that is the most numerous and widespread species, forms the largest colonies, and is the species seen in Texas. The black-tailed is native to the Great Plains of North America from northern to southern borders with Canada in southern Saskatchewan to Chihuahua, Mexico. One of the largest black-tailed colonies on record was documented by American naturalist and mammalogist, Vernon Bailey during the Biological Survey of Texas (1889-1905). The colony stretched from San Angelo to Clarendon in the Texas Panhandle and was 100 miles wide and covered about 25,000 square miles. It was estimated to have had a population of about 400 million prairie dogs. Black-tailed prairie dogs still occupy most of their historic range, but well below historic levels.
Black-tailed prairie dogs have a most sophisticated social structure. They live in colonies ranging in size from five to many thousands of individuals. Colonies are divided into two or more wards based on the topography of the land. Wards are further subdivided into two or more coteries composed of aggregates of territorial, harem-polygynous social groups. Individuals within a coterie are amicable with each other but hostile to members of another coterie. The population and growth of a coterie may be influenced by the quality of habitat, topographic barriers, soil type, vegetation height, and social conditions. At the beginning of the breeding season, a coterie is composed of a single adult male, three or four adult females, and several yearlings and juveniles of both sexes. Coteries typically occupy about one acre in space. After the breeding season, but before the dispersal of the juveniles, the size of a coterie increases. There may be several reasons for the dispersal of the juveniles: there may be new vegetative growth at the edge of a colony as an enticement; there may be a shortage of unrelated females within a coterie, or harassment of females by juveniles; dispersal can also be an innate response to population density. Males leave their birth territory 12-14 months after weaning (usually May-June), but dispersal may occur at any time; however, females usually remain within their birth coterie for life. The distance of dispersal is about one and a half miles from the birth site.
Black-tailed prairie dogs are diurnal, but their above ground activities decrease with rain or snow, or when summer temperatures exceed 100 degrees F. They are selective opportunists in their diet, preferring certain types of vegetation depending on their needs. Grasses are preferred, especially in the spring and summer, but they will also eat insects. Most of their water needs are provided metabolically from vegetation. In winter, they do not hibernate and sometimes exit their burrows to forage, but at night they enter a state of torpor to conserve energy.
Black-tailed prairie dogs are vocal communicators. There is evidence that they may use specific calls to describe specific predators. But the most conspicuous call is the familiar “jump-yip” display. When one starts a display, others nearby soon join in. They are watchful neighbors, but there is debate as to whether the displays are selfish or altruistic. Predators abound…coyotes, badgers, bobcats, golden eagles, red-tailed and ferruginous hawks, and prairie rattlesnakes. Although exceedingly rare now, the black-footed ferret was once a major predator.
Burrows are refuges from predators and the external environment. Burrows are also used for breeding and rearing of the young. Nests in a burrow are lined with dried grasses collected throughout the year and gathered by males, females, and juveniles. There are three types of burrow entrances: dome mounds, rimmed crater mounds, and entrances without surrounding structure. The construction of a burrow entrance may aid in flood control during rain as well as tunnel ventilation. Most colonies have from 20 to over 50 burrows per acre at depths of 50-60 inches. Burrows are maintained from generation to generation and contribute to the stability on both the physical and social aspects of a colony, most notably at the coterie level.
Prairie dogs are ecosystem engineers. Their burrowing activities influence the heterogeneity of the environment influencing the landscape, hydrology, nutrient cycling, plant succession, and biodiversity of the grassland prairie. The prairie dog’s preference of habitat is also influenced by vegetative cover, slope of the land, and soil type. Optimal conditions are slopes between 2% and 5% and vegetation height between 3 and 5 inches. They also prefer soils that are not prone to collapsing or flooding. Soil horizons become mixed due to their burrowing activities. On the Great Plains, colonies are frequently located near rivers and creeks and near playas on the Llano Estacado.
Although not universally accepted, prairie dogs are considered by some researchers to be a keystone species in some areas. There is evidence that supports enhanced diversity of vegetation, vertebrates, and invertebrates from their foraging and burrowing activities and by their presence as a prey item. Grasslands with prairie dogs have greater biodiversity than grasslands without. Abandoned burrows are used by horned lizards, spadefoot toads, and tiger salamanders. But the most charismatic occupant of an abandoned black-tailed prairie dog hole is the Western Burrowing Owl (Athene cunicularia hypugaea).
A fascinating symbiotic relationship occurs between the black-tailed prairie dog and the western burrowing owl. Burrowing owls nest and roost in burrows such as those excavated by prairie dogs. Unlike most owls, burrowing owls are often active during the day. The retinal layer of their eyes lack a developed tapetum lucidum, the retroreflective layer contributing to night vision in nocturnal animals. They also lack the acute binaural hearing and sound-source location abilities of other owls. Burrowing owls are good flyers, but they have proportionately longer legs for sprinting after prey when hunting. When threatened, the owl retreats into the burrow and frequently produces the rattling and hissing sounds of a rattlesnake. This acoustic Batesian mimicry is an effective strategy against predators familiar with the dangers of rattlesnakes.
One unique behavior of the burrowing owl is the strategic placement of fecal matter from large herbivorous mammals around the outside of the burrow. The strategically placed droppings may help to mask the odors of an active owl burrow from predators like badgers, but the droppings may also attract insects like dung beetles---a steady source of food for the owl, especially in the summer. An active owl burrow will have strewn about owl pellets rich in the fragments of chitinous insect exoskeletons. Burrowing owls have a highly variable diet of mostly large insects and small rodents, but they have been known to take appropriately sized frogs, toads, snakes, lizards, and turtles. Burrowing owls are also known to eat the fruits and seeds of tasajillo, prickly pear, and cholla cacti.
In the exploitation of prairie dog burrows, burrowing owls favor larger and more active colonies with a preference of holes at the periphery and often when there are several “satellite” burrows available. Towns that have been abandoned by prairie dogs will also be abandoned by burrowing owls---usually within three years due to the encroachment of taller, denser vegetation and a gradual deterioration of the burrows themselves.
Being migratory, the burrowing owl is federally protected under the Migratory Bird Treaty Act, but their symbiotic relationship with the black-tailed prairie dog has led to their decline. The greatest threat to burrowing owls is the destruction and degradation of habitat primarily from land development and prairie dog control measures. So, attitudes toward prairie dogs have a direct bearing on burrowing owls. The prairie dog represents varmint, keystone species, ecosystem engineer, and disease vector depending on one’s point of view. The cause of their controversy (their burrowing and grazing activities) is the same reason they are important. They have a significant impact on the prairie ecosystem. They are prolific diggers constructing complex burrow systems with specifically dedicated chambers that can cover thousands of acres. But this subterranean system houses more than just prairie dogs; numerous vertebrate and invertebrate species are also impacted. European immigrants viewed the prairie dogs as destructive vermin and the colonization of the West led to the current conservation dilemma. The conversion of prairie to agricultural land has destroyed habitat and systematic poisoning has removed colonies from land set aside for grazing by cattle. The accidental introduction of fleas carrying sylvatic plague (Yersenia pestis) (the same bacterium that causes bubonic plague in humans) can wipe out entire colonies within months. These factors have contributed to a 95% decline in the numbers of prairie dogs. But this represents more than a loss to one species, but rather to a suite of species supported by prairie dog ecosystem engineering. Prairie dog landscaping creates short grass habitat for many species---especially birds (ex. horned lark, long-billed curlew, mountain plover, and McCown’s longspur, and of course, burrowing owls).
Prairie dogs consume many of the same grass species as cattle, so they are still widely perceived as threats. But hard evidence of actual competition is mixed. In some regions, prairie dogs may help maintain grassland habitat beneficial for cattle. Some studies have shown that the nutritional quality of grasses is increased by prairie dog grazing. Prairie dog landscaping also helps to prevent the encroachment of woody shrubs like mesquite. It is still a hotly debated and nuanced issue, so more research is needed.
I wish to extend my thanks Debbie Whiting for permission to use her photographs of the black-tailed prairie dog and to Susan May for her photographs of burrowing owls. All photographs were taken at the prairie dog colony at Lamesa Road and Loop 250 in Midland, Texas.
For further reading on prairie dog society, behavior, and ecology:
Hoogland, John L. The Black-tailed Prairie Dog: Social Life of a Burrowing Mammal. University
of Chicago Press, 1995.
Knowles, Craig J. “Some Relationships of Black-Tailed Prairie Dogs to Livestock Grazing.” Great
Basin Naturalist: Vol. 46: No. 2, Article 2, 1986.
Long, Dustin and Joe Truett. “Ranching and Prairie Dogs.” USDA Forest Service Proceedings
Olsen, Kenneth C., et.al. “Effect of Grazing Prairie Dogs---Colonized Rangeland on Cattle
Nutrition Performance: A Progress Report.” Rangelands Vol. 38, Issue 1 February 2016, pp. 29-
Slobodchikoff, C.N., Bianca Perla, and Jennifer Verdolin. Prairie Dogs: Communication and
Community in an Animal Society. Harvard University Press, 2009.