Cynomys mexicanus

Geographic Range

The Mexican prairie dog ( Cynomys mexicanus ) is endemic to Mexico in a restricted range of approximately 500 km² in northwestern Mexico, in the states of Coahuila, Nuevo Leon, and San Luis Potosi. Historically, they were also found in the state of Zacatecas. Currently, 74% of their range is found in Nuevo Leon, 24% in Coahuila, and only 2% in San Luis Potosi. Their distribution is limited to the north and west by the Sierra Madre Oriental, and to the south and east by semi-arid hills and grasslands. They have not been introduced anywhere else in the world.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

The Mexican prairie dog is found at elevations between 1600 and 2200 meters. The species is restricted to 6 large, arid grassland valleys and intermontane basins in Mexico, specifically the Mexican Plateau. These grasslands are found at the base of larger valleys and basins, and form one phase of a semi-arid shrub mosaic. They are strongly associated with outcrops of gypsum soils, which are of low productivity. The gypsum rock found in these soils originate from eroded marine sediments deposited during the Pleistocene . The habitat is commonly surrounded by arid scrub and contains short grasses typical of calcareous and gypsophyllum soils such as creeping muhly ( Muhlenbergia repens ) and burrograss ( Scleropogon brevifolius ). Mexican prairie dogs excavate exploratory burrows in rocky, sandy, and clay soils; however, very sandy soils are unfavorable for burrowing. They may be able to colonize or re-colonize former croplands if the soil composition provides good structural support and depth for burrowing. Prairie dogs of all species avoid steeply sloped areas due to decreased predator detection in these habitats. In addition, sloped environments are often very rocky and thus provide poor habitat for fossorial animals.

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• desert or dune desert or dune
• savanna or grassland savanna or grassland

Physical Description

Mexican prairie dogs are one of the largest species in the Cynomys genus, only slightly smaller than black-tailed prairie dogs , from which they are hypothesized to have diverged from approximately 42,000 years ago. Adults range in mass from 300 to 900 grams in the spring, and 500 to 2000 grams in the fall. Their total length ranges from 385 to 440 millimeters. When standing, they reach a height of approximately 30 cm. Although males and females have similar coloration, males are about 15% larger than females. Individuals from the southern limits of their geographic range tend to be larger than those from northern areas. Similar to black-tailed prairie dogs , Mexican prairier dogs have two distinct coats, one during the summer and one with thick underfur during the winter. The distal half of the tail is black, which distinguishes them in appearance from most other species in the genus. Mexican prairie dogs have blunt noses and small mouse-like ears. They have five digits on each foot, and each digit has a thick, black, curved claw. They also have many black whiskers that can reach 3 cm in length. The pelage has a grizzled effect, as individual hairs covering its body have four bands of color: black at the proximal end, then white, red, and yellow at their tips. Their tail, which makes up more than 20% of their total body length, ranges from 83 to 115 mm, and has black hairs along the lateral margins as well as the tip. Unlike black-tailed prairie dogs and white-tailed prairie dogs , mexican prairie dogs do not have a black or dark brown line above the eyes.

Mexican prairie dogs molt two times a year. Their spring pelage, which is present by March or April, is characterized by a heavy coat with think underfur. They begin molting their spring coat in September. Their winter coat, which most individuals have in full by early November, contains dense underfur that helps retain heat. Each molting period lasts about two weeks, and unlike other members of the genus who shed anteriorly to posteriorly, Mexican prairie dogs shed irregularly and patchily.

Mexican prairie dogs have large auditory bullae, which allow them to hear sounds ranging from 29 to 26,000 Hz, with peak hearing occurring between 500 and 4000 Hz. They have triangular cheek teeth and broad nasals that are posteriorly truncated. Similar to other Cynomys species, they have wide zygomatic arches and well defined zygomatic processes. Their dental formula is I 1/1, C 0/0, P 1/1, M 3/3 (total = 20), and they have bright yellow upper incisors that contain grooves on the interior surfaces. Complete permanent dentition occurs in juveniles within 2 or 3 months after emerging from the burrow during their first year.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Reproduction

Mexican prairie dogs are polygynous and commonly form groups of females that reside within their mother's territory resulting in large clans or colonies (i.e., matrilocal harems). Males give out a mating call that resembles an alarm call. If a female wishes to mate, it permits the approach of a sexually active male. Breeding takes place underground, and therefore little is known of copulation behavior in this species.

• Mating System
• polygynous polygynous

Mexican prairie dogs reproduce once per year, with litter sizes ranging from 1 to 6 pups and an average of 4. Gestation lasts 30 days, from early March to early April, after which altricial young are born pink, hairless, and blind. Skin pigmentation occurs after 12 days, and hair begins to develop after approximately 2 weeks. Young have full pelage by 3 to 4 weeks and their eyes open around 4 to 5 weeks after birth. Neonates weigh between 15 and 20 g, and the mean mass of juveniles upon emergence from their burrow varies inversely with litter size. Males are slightly heavier than females upon emergence, corresponding with the adult sexual dimorphism of the species. Juveniles reach adult weight at approximately 6 months of age. Pups are nursed for 40 to 50 days, and weaning typically occurs around 45 to 50 days after birth. Females have 8 mammae, unlike some Cynomys species, which have 10 (e.g., white-tailed prairie dog ). Teats become elongate and swollen during late pregnancy and remain so until weaning is complete. Juveniles remain underground for 5 to 6 weeks, after which they emerge independent of parental care.

Both males and females may begin mating before one-year-old, however males typically wait until two years of age. Breeding season usually begins at the end of January and can extend into March, lasting about 90 days. Males begin producing sperm in December, just prior to the onset of breeding season, and discontinue sperm production in April. Males have a baculum, a penis bone found in most mammals that aids in intercourse, that averages 4.92 mm. The baculum is narrow at the base and broad at the distal end, which has 5 to 8 spines. Females become sexually active when their vulva becomes swollen and white. Estrus is very short, averaging 1 day in early March. Estrus of all females in a colony is asynchronous, which helps decrease intracolony competition for mates. Breeding season in Mexican prairie dogs is longer than in most other Cynomys species due to the climatic conditions of the Mexican Plateau where they are found. Decreased seasonality at lower latitudes allows for a longer breeding season, however, the the quality and abundance of food exhibits marginal variation between seasons.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• viviparous viviparous

Although responsibilities differ, both genders provide care to their young. Male and female Mexican prairie dogs allogroom, play with young, maintain burrows, and nest-build. Males are primarily responsible for territorial defense. Females nurse young for 40 to 50 days and weaning occurs at 45 to 50 days after birth. Juveniles remain underground for 5 to 6 weeks, after which they are fully independent and emerge from their burrows. Although infanticide is known to occur in white-tailed prairie dogs and Utah prairie dogs , there have been no known reports of infanticide occuring in Mexican prairie dogs.

• Parental Investment
• altricial altricial
• male parental care male parental care
• female parental care female parental care
• pre-hatching/birth
  • provisioning
    • female
• pre-weaning/fledging
  • provisioning
    • male
    • female
• pre-independence
  • provisioning
    • male
    • female
  • protecting
    • male
    • female

Lifespan/Longevity

The percentage of juveniles that survive at least one year is directly correlated with body mass upon emergence from the burrow. Juveniles with higher body mass have a better change of survival. Although the lifespan of Mexican prairie dogs has not been documented, male black-tailed prairie dogs do not live longer than 5 years, but females may live up to 8 years of age.

It has been suggested that sylvatic plague could be devastating to the survival of Mexican prairie dogs. Sylvatic plague is a serious infectious disease caused by the bacterium Yersinia pestis , which is transmitted by the flea species Pulex simulans and Opisocrotis hirsutus . These flea species, both of which have been found on Mexican prairie dogs, can be transmitted by other rodents or predators. Surprisingly, no cases of sylvatic plague have been reported in Mexican prairie dogs.

Behavior

Mexican prairie dogs are diurnal, and come above ground during daylight hours, spending more than half of their lifetime in burrows. This daylight emergence is consistent with the high number of cones and small number of rods within their retinas. They spend more than 95% of daylight hours aboveground. If temperatures rise above 27°C, they submerge into their burrows to cool off, sometimes remaining underground until late afternoon. They are known to have one or two daily activity peaks, and do not hibernate. Mexican prairie dogs are highly dependent on fat reserves during long periods of warm temperatures.

Mexican prairie dogs are highly social animals, living in harem family groups called coteries. These coteries typically contain one breeding male, two or three adult females, and one or two yearlings, and average 6.13 individuals per coterie. Individual coteries are found in close proximity of each other, creating colonies of up to 100 individuals. Within a coterie, resident animals engage in both friendly and aggressive behaviors. Friendly behaviors include a greet-kiss, play, and allogrooming, while aggressive behaviours include chasing, fighting, facing each other while fluffing out their tails, and chasing conspecifics away from individual feeding grounds. Regardless of gender, heavier individuals exhibit dominance during aggressive interactions over lighter individuals. Occasionally, hostile interactions between coteries within a single colony occur, as individuals defend territories from other coteries.

Dominance hierarchies occur within coteries. Reproductive males (e.g., males who have copulated during the current reproductive season) are dominant and regularly initiate and win aggressive encounters with lighter non-reproductive males. If a coterie contains two breeding males, the heavier male holds dominance over the other, although two breeding males of the same size show no difference in dominance behavior. Heavier females gain a reproductive advantage by copulating earlier than lighter females, and heavier pregnant and lactating females dominate lighter and non-reproductive females in behavioural interactions.

Dispersal is male biased, and dispersal distance ranges from 2 to 3 km. Adult males disperse long distances, resulting in high levels of genetic heterogeneity within populations. The establishment and expansion of colonies requires that individuals select open areas or remove vegetation in prospective expansion area.

• Key Behaviors
• terricolous
• fossorial fossorial
• diurnal diurnal
• motile motile
• territorial territorial
• social social
• dominance hierarchies dominance hierarchies

Home Range

Each coterie occupies an area containing one or more burrow openings, an underground burrow system, and food resources growing in the territory. These boundaries are defended by all members of the group. Burrow openings are spaced several meters apart and are characteristically marked by a mound of dirt ranging from 0.5 to 1.5 m in diameter and 0.2 to 1.0 m high. These mounds, known as rim craters, serve as observation posts for spotting potential predators. The openings are 10 to 30 cm in diameter, and are much narrower underground. Burrows are usually 5 to 10 m long and 2 to 3 m deep, but can reach lengths of up to 33 meters and depths of up to 5 meters. Inside the burrows, chambers approximately 30 cm high and 50 cm wide are used to rear young and sleep, and are packed with dry grass collected by all members of the coterie. Often, they create a series of 4 to 7 short, shallow escape burrows 8 to 10 m away from their nest burrows. Escape burrows increase the area in which they can forage, while experiencing minimal risk of predation.

Communication and Perception

Communication between Mexican prairie dogs is extensive, and occurs in three forms: vocal signals, visual signals and olfactory cues. Visually, the animal may wag its tail (tail-flagging), characterized by a raised tail with the tail fur piloerected, followed by a back and forth wag when a predator is nearby. Although it has not been documented in Mexican prairie dogs, some Cynomys species stand upright in an alert posture (i.e., posting), which allows them to see predators more easily and makes them visible to other prairie dogs in the local area. Mexican prairie dogs are known to drag their rump along the ground, which is thought to be a way of leaving olfactory marks from their anal glands.

Mexican prairie dogs perform a "greet-kiss" in which two prairie dogs in the same coterie open their mouths, and press their tongues together. This lasts only one or two seconds, after which the animals continue with their prior activities. This also occurs between members of different coteries, and after the kiss, the resident individual will chase the intruder out of the territory. They likely to have oral glands as well, which may help conspecifics identify each other during the greet-kiss. Greet-kissing occurs between two males, two females, or a male and a female, and between individuals of any age. This may help identify individuals based on taste or smell, as physical differences between individuals appear minor. It may also provide information about food the individual has been eating or may serve a function in the establishment or maintenance of the local hierarchical structure.

The most important communications that occur between prairie dogs are vocalizations. These calls are nearly indistinguishable from calls of their close relatives, the black-tailed prairie dogs , and include barks, snarls, growls, screams, and yips. Alarm calls sound similar to the bark of a small dog, which is how the prairie dog got its name. Alarm calls are used when a potential threat has been detected. Although calls do not change based on predator type (e.g., terrestrial vs. aerial), they increase in rate (i.e., barks per minute) when a predator is closer. Mexican prairie dogs have a repetitive single syllable bark, unlike those of black-tailed prairie dogs which consists of two syllables. One of the more common calls used by Mexican prairie dogs is known as a jump-yip call. When performing the jump-yip calls, an individual stands on its hind legs, reaches upward with its front legs, and emits a "yip" vocalization. This call is commonly repeated by nearby animals after hearing the initial call, and travels through all the prairie dogs in the area. This call is thought to serve as an all-clear signal when a predator leaves the territory, or as a warning signal when a predator is nearby. Tooth chattering also occurs during interactions with conspecifics, where the animal will click its incisors together emitting sounds that can be heard between 5 and 100 m away.

• Communication Channels
• visual visual
• acoustic acoustic
• chemical chemical

• Other Communication Modes
• mimicry mimicry
• duets duets
• choruses choruses
• pheromones pheromones
• scent marks scent marks

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Prairie dogs are herbivorous, and population growth is directly affected and limited by forage availability. During periods of active plant growth, feeding efforts are focused on stems and leaves, but at other times focus on forbs, cacti, and yucca. Grasses dominate their diet during April and May, while forbs dominate during June, July, and August. Throughout the remainder of the year, their diet is an equal mix of both grasses and forbs. Overall, forbs account for nearly 60% of their annual diet, shrubs account for 14% to 17% annually, and grasses account for approximately 22%. This switch in diet may be due to the decrease in nutritional quality of grasses as they mature, and suggests that Mexican prairie dogs strive to maintain a high quality diet year round. Mexican prairie dogs are known to forage on Croton dioicus , Sphaeralcea angustifolia , Solanum elaeagnifolium , and Setaria leucophyla .

• Primary Diet
• herbivore herbivore
  • folivore folivore

• Plant Foods
• leaves
• roots and tubers

Predation

Mexican prairie dogs have a wide range of predators, both terrestrial and aerial. Terrestrial predators include gray foxes , bobcats , cougars , and a variety of rattlesnakes . Aerial predators include golden eagles , peregrine falcons , prairie falcons , and northern goshawks . Despite their many predators, Mexican prairie dogs appear to have high a survival rate and researchers rarely see predation occurring under natural conditions. Their colonial lifestyle likely increases their per-capita survival rate. Individuals crop local vegetation within the colony's habitat to about 30 centimeters tall. Decreased cover allows for earlier predator detection, and living in large social groups allows individuals to spend more time feeding rather than constantly scanning for predators.

Ecosystem Roles

The Mexican prairie dog is considered a keystone species in the Mexican Plateau, helping to support an ecosystem full of predators, prey, insects, and plants. They have a significant impact on soil composition, excavating large burrow systems and creating strong bottom-up effects. Burrowing leads to aeration of the soil, cycling of nutrients, and changing the soil texture. By eating only certain plants and grazing, they play an active role in altering the diversity and abundance of local plant communities.

Cattle commonly use prairie dog habitat for grazing, and diet overlap between these two species has been documented, however, there is no evidence suggesting interspecific resource competition. Grazing by cattle may lead to soil erosion that can alter the gypsum surface and threaten prairie dog colonies. Dietary overlap and interspecific resource competition has been documented between Mexican prairie dogs and Audobon's cottontails , and dietary overlap (and possible competition) has been documented with sheep. Because Mexican prairie dogs are a keystone species, declining populations are resulting in a domino effect, which has caused other species to be threatened or endangered.

Mexican prairie dogs exhibit exceptionally low levels of parasitism. Other prairie dog species are host to protozoans , tapeworms , roundworms , and spiny-headed worms , so it possible that Mexican prairie dogs do as well. Mexican prairie dogs are known to host numerous species of parasitic arthropods, including fleas , lice , and ticks . Fleas are most common before the breeding season, and an individual may have up to 300. Autogrooming is often displayed with individuals scratching, biting or licking themselves to remove these parasites.

• Ecosystem Impact
• biodegradation biodegradation
• soil aeration soil aeration
• keystone species keystone species

Economic Importance for Humans: Positive

Prairie dogs excavate large burrow systems, and this causes subsurface soil to mix with surface soil. This excavation can lead to increased porosity of the soil, therefore allowing water to penetrate deeper, and increase groundwater recharge. This in turn adds organic matter and nutrient salts to the soils, increasing benefits to the plants and organisms living in the soil, thus making them more abundant. Livestock commonly feed on these plants, and higher abundance translates to more food available and healthier livestock for farmers. This is contrary to popular belief that cattle compete with prairie dogs for food and the reason prairie dogs are considered pests to farmers, and often poisoned. In the past, Mexican prairie dogs were an important food source for Native Americans and European explorers, however this no longer occurs. Scientific interest in Mexican prairie dogs has increased due to the realization that their populations are declining. Prairie dogs of all species are important subjects in behavioral ecology, helping scientists understand social behavior in mammals, demography, alarm calling, and kin recognition.

• Positive Impacts
• pet trade pet trade
• research and education

Economic Importance for Humans: Negative

In the same way that the burrows of Mexican prairie dogs have positive impacts, they also cause an increase in calcification of surface soil which accelerates the process of erosion due to the increased amount of bare land. Farmers also believe that burrows cause livestock to stumble into openings and break their legs, although fractures of this type rarely occur.

• Negative Impacts
• crop pest

Conservation Status

Humans have played a significant role in the decline of Cynomys mexicanus . Recreational shooting, modification of land for agricultural purposes, soil erosion by cattle herding, and eradication programs have all contributed to their declining numbers. Habitat destruction has caused resources to become limited, and the continued loss of grassland habitat prevents the recovery of the species. Habitat fragmentation and a small geographic range have resulted in Cynomys mexicanus being listed as endangered by the IUCN (International Union for Conservation of Nature and Natural Resources). Over the past four decades, 62% of C. mexicanus habitat has been lost due to human impact. Population densities are lower in the southern extremities of their geographic range, which likely results in higher extinction rates in these areas. Transplantation of individuals from northern areas has been suggested to help with conservation, as natural recolonization alone will not reverse their endangered status. Cynomys mexicanus is fully protected by Mexican law, although it is only in Racho Los Angeles, Coahuila where any substantial protection is enforced.

Additional Links

Encyclopedia of Life

Contributors

Stephanie Hardy (author), University of Manitoba, Jane Waterman (editor), University of Manitoba, John Berini (editor), Animal Diversity Web Staff.

References

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