Gunnison's Prairie Dogs Research Articles

Estrus and Copulation of Gunnison's Prairie Dogs

Because most animals copulate surreptitiously, estimates of male and female copulatory success are elusive. Here I describe six distinctive behaviors that coincide with underground copulations of Gunnison's prairie dogs ( Cynomys gunnisoni ): the underground consortship itself, inordinate male attention toward the estrous female, self-licking of genitals, dustbathing, the mating call, and late final submergence of the estrous female. These diagnostic behaviors allowed me to identify sexual partners for 308 females that came into estrus during a 7-year study.

Why do female Gunnison's prairie dogs copulate with more than one male?

A female can usually obtain enough sperm to fertilize all her eggs from a single insemination, and copulation involves certain costs such as increased exposure to diseases and parasites. Why, then, do females of so many species routinely copulate with more than one male? A 7-year study of marked individuals provides an answer for 239 female Gunnison's prairie dogs (Sciuridae:Cynomys gunnisoni) living under natural conditions. The probability of pregnancy and parturition was 92% for females that copulated with only one or two males, but was 100% for females that copulated with at least three males. Further, litter size at weaning varied directly with the mother's number of sexual partners.

Dynamics of plague in a Gunnison's prairie dog colony complex from New Mexico.

A plague (Yersinia pestis) epizootic spread through Gunnison's prairie dogs (Cynomys gunnisoni), and possibly other rodent species, in the Moreno Valley in north-central New Mexico between winter 1984-1985 and autumn 1987. We observed the progress of the epizootic and subsequent population recovery at four prairie dog towns within the valley during this period. At two towns (Midlake and Val Verde) the prairie dogs were marked prior to the epizootic. At two additional towns (Vega and South Entrance) prairie dogs were marked following the epizootic. In 1988, a second epizootic occurred at Vega. One hundred thirty-nine serum samples were collected from prairie dogs and other rodents and 1,750 fleas were collected from animals and burrows. Fleas infected with Y. pestis were collected from prairie dogs, deer mice (Peromyscus maniculatus), and thirteen-lined ground squirrels (Spermophilus tridecemlineatus). Prairie dog fleas included Oropsylla hirsuta, O. labis and O. tuberculata, deermouse associated fleas were Aetheca wagneri and Rhadinopsylla sectilis, and Oropsylla bacchi was associated with thirteen-lined ground squirrels. All of the above flea species were collected from prairie dog burrows. All rodent species shared some flea species. Thirteen-lined ground squirrels disappeared shortly before plague was identified in prairie dogs at Midlake. Meadow voles were rare following the epizootic at Vega in 1986, became abundant in 1987, and disappeared at the time of the second prairie dog epizootic in summer 1988. Although we collected serum from Gunnison's prairie dogs, thirteen-lined ground squirrels, deer mice, and meadow voles (Microtus pennsylvanicus), we identified elevated serum titers against Y. pestis only in Gunnison's prairie dogs. Prairie dog mortality at all towns affected by plague was in excess of 99%. Serum antibody titers indicate that more than 40% of the few prairie dogs left to establish colonies following epizootics survived plague infection.

DNA Fingerprinting Reveals Low Genetic Diversity in Gunnison's Prairie Dog (Cynomys gunnisoni)

The use of molecular techniques for the assessment of familial relationships among social species of mammals has become relatively commonplace. However, some species represent poor candidates for such studies due to naturally low levels of genetic diversity, leading to unacceptably large standard errors associated with estimates of relatedness. Here, we report on a preliminary study of genetic diversity within two populations of a social species of ground squirrel, Gunnison's prairie dog ( Cynomys gunnisoni ) using DNA fingerprinting. We observed low levels of diversity in the form of large mean coefficients of genetic similarity among individuals occupying the same population. Overall similarity, determined from the combined data, yielded by three minisatellte probes, ranged from 55 to 61%. These values place Gunnison's prairie dog at the extreme upper end of the range of similarity values reported for outbred species of mammals (ca. 0.20-0.50). As a partial means of explaining these results, and as a means of comparing our results to those of similar studies using allozymes, we determined the level of differentiation between our two study colonies in the form of an F -statistic analog. A value of 0.11 (± 2.26 × 10−3) was obtained and is similar to values reported from allozyme studies (0.07–0.12). A significance test of this value yielded a positive result (D = 5.63, d.f. = 1, P < 0.025), demonstrating that gene flow between populations is limited, a factor that may help to maintain low levels of diversity.

Growth and Life-History Changes in Gunnison's Prairie Dogs after a Plague Epizootic

I measured rates of growth of individual Gunnison's prairie dogs ( Cynomys gunnisoni ) at three towns in the Moreno Valley, New Mexico; at an established prairie dog town (site 1) prior to a plague ( Yersinia pestis ) epizootic and at two towns reestablished after the epizootic (sites 2 and 3). Populations declined by >99% during the epizootic. After the epizootic, adults had greater mass, and juveniles grew faster than before. At sites 2 and 3, juveniles had high interyear survival (39%), whereas at site 1, prior to plague, survival of juveniles was 17%. At sites 2 and 3, yearlings bred, whereas they did not at site 1. Mean litter size near the end of lactation was 1.5 at site 1 and 5.0 at sites 2 and 3. Application of observed demographic parameters to Leslie-matrix analysis indicated that projected size of population was declining (λ = 0.829) at site 1 and was tripling annually (λ = 2.905) at sites 2 and 3. The difference in λ was mostly due to increased survivorship of juveniles and reproduction at an earlier age in the new towns.

Duration of Gestation and Lactation for Gunnison's Prairie Dogs

The length of gestation is the number of days between fertilization and parturition, and the length of lactation is the number of days between parturition and weaning. Determination of these lengths is difficult for ground-dwelling squirrels such as prairie dogs, marmots, and ground squirrels that usually copulate, give birth, and nurse offspring underground. For Gunnison's prairie dogs ( Cynomys gunnisoni ), the mean ±1 SD length of gestation is 29.3 ± 0.53 days ( n = 124). The approximate length of lactation, estimated from the mean ± 1 duration between parturition and the first emergence of juveniles from the natal burrow, is 38.6 ± 2.08 days ( n = 112).

Why do Gunnison's prairie dogs give anti-predator calls?

At a colony of Gunnison's prairie dogs, Sciuridae: Cynomys gunnisoni, containing marked individuals of known genetic relationships, anti-predator calling was investigated in response to moving, stuffed specimens of a natural predator, the American badger, Taxidea taxus. Females with kin in the home territory called more often than females without nearby kin, and females with nearby offspring were especially likely to call. Male gunnisons commonly gave anti-predator calls as well, but male calling was unrelated to kinship of nearby listeners. 1996 The Association for the Study of Animal Behaviour

Social assemblages and mating relationships in prairie dogs: a DNA fingerprint analysis

Mating system characterizations have been hindered by difficulties in accurately assigning parentage to offspring. We investigated the relationship between social assemblages and mating relationships in a territorial harem polygynous mammal, the Gunnison's prairie dog, using a combination of behavioral and molecular analyses. We demonstrate multiple paternity and an extraordinarily high incidence of extraterritorial fertilizations (i.e., 61% of all progeny), in combination with the existence of female kin groups. On this basis, we conclude that social assemblages alone provide a poor description of the Gunnison's prairie dog mating system, and suggest several potential reasons for the maintenance of territoriality in this species.

Ecological and Demographic Effects on Intraspecific Variation in the Social System of Prairie Dogs

Gunnison's prairie dogs (Cynomys gunnisoni) are social North American ground squirrels whose social system has been shown to vary with food resource distributions, as predicted by the habitat variability–mating system model. We expanded this model to include the effects of variations in population densities, in addition to resource distributions, on both the social system and the individual mating strategies of Gunnison's prairie dogs. Specifically, we predicted that monogamy would be associated with uniform resources, regardless of population density, giving way to polygyny with increasing resource patchiness at intermediate densities, and to multiple males and females at high population densities. In addition, we predicted inbreeding at low densities and outbreeding at high densities on the basis of naturally low levels of genetic eity in this species. We tested these predictions by comparing social systems and mating strategies at two prairie dog colonies near Flagstaff, Arizona, during a 3—yr period of population increase. We observed variations in sociality to vary in the predicted fashion at both colonies, providing support for the plant patchiness–population density model.

Effects of food resource distribution on the social system of Gunnison's prairie dog (Cynomys gunnisoni)

We tested the predictions of Slobodchikoff s habitat variability – mating system model using the social system of Gunnison's prairie dog (Cynomys gunnisoni). The model predicts that when resources are abundant and patchily distributed, social groups will include several females, while scarce, uniformly distributed resources will lead to smaller groups with single females. Gunnison's prairie dogs form family groups consisting of a single adult male and female(s), and their young of the year, which occupy fixed spatial territories within a colonial framework. Resource abundances and distributions were characterized and compared at two colonies in northern Arizona. Resource abundance did not vary between colonies, while two separate measures showed resource distribution to be significantly more patchy at one colony than at the other. As predicted, there were significantly more territories with multiple females at the patchy colony, while single-female territories predominated at the uniform colony. While the differences in resource abundance between colonies were not significant from a statistical standpoint, sizable differences were observed, with the direction of the difference opposite to that predicted by the model.

Semantic information distinguishing individual predators in the alarm calls of Gunnison's prairie dogs

Gunnison's prairie dogs, Cynomys gunnisoni, are colonial social rodents that give alarm calls upon the approach of a predator. Field experiments at two natural colonies showed that the prairie dogs are able to encode information into their alarm calls about the colour of clothes and general shape of individual humans eliciting alarm calls. This shows that the prairie dogs are able to incorporate information about the characteristic features of individuals within a given predator category.

Social behavior and space-use of young of ground-dwelling squirrel species with different levels of sociality

Comparisons among young of ground-dwelling squirrel species with different adult sociality indicate patterns of interaction during development that may influence the evolution of complex sociality. Social behavior and spatial overlap of weaned young with their mothers, littermates, non-littermate young, and adult conspecifics were compared among Gunnison's prairie dogs (Cynomys gunnisoni), yellow-bellied marmots (Marmota flaviventris), Columbian ground squirrels (Spermophilus columbianus), and thirteen-lined ground squirrels (S. tridecemlineatus). The adult social organization of these species differs markedly: Gunnison's prairie dogs are highly social, yellow-bellied marmots and Columbian ground squirrels are relatively less social, and thirteen-lined ground squirrels are asocial. In young Gunnison's prairie dogs, social cohesion and spatial overlap were high not only with the mother and littermates, but with all members of the harem. In yellow-bellied marmots, social cohesion occurred with all members o...

Response of Raptors to Reduction of a Gunnison's Prairie Dog Population by Plague

-Raptors were counted at approximately 2-week intervals between March and November 1985-1987 in the Moreno Valley, Colfax Co., New Mexico. During that period, an epizootic of plague (Yersinia pestis) swept through the valley and sequentially killed Gunnison's prairie dogs (Cynomys gunnisoni) n three areas of approximately 25 km2 each. Red-tailed hawk (Buteo jamaicensis) numbers did not change significantly over the study period. Although golden eagles (Aquila chrysaetos) declined in abundance, their numbers did not recover with the recovery of prairie dogs in 1987. Ferruginous hawks (B. regalis) were abundant during autumn migration where prairie dogs were abundant, but their numbers declined significantly with the population decline of prairie dogs. Gunnison's prairie dogs appeared to be an important food resource for ferruginous hawks during their migration through the Moreno Valley.

Seasonal Changes in the Diet of Gunnison's Prairie Dog

Seasonal Changes in the Diet of Gunnison's Prairie Dog

Social organization and space-use in Gunnison's prairie dog

Social organization of the Gunnison's prairie dog, Cynomys gunnisoni, was studied in two populations in south-central Colorado. Gunnison's prairie dogs live in complex, interactive societies fitting current definitions of highly social ground squirrels. Members of harems (‘coteries’) cooperatively use and defend a common territory. Spatial overlap is extensive between the adult male(s) and adult females, and among adult females within the harem through the active season. Amicable behavioral interactions are frequent within the harem, whereas interactions between members of different harems are primarily agonistic and spatial overlap is minimal. Although their behavioral repertoire is more limited, social organization of the Gunnison's prairie dog most closely resembles that of the black-tailed prairie dog, C. ludovicianus. Although body size, age of first reproduction, and age of emigration differed between the two study populations (Rayor 1985a), a comparison of social traits did not reveal substantial differences.

Hibernation in the Gunnison's Prairie Dog

Hibernation in the Gunnison's Prairie Dog

Effects of habitat quality on growth, age of first reproduction, and dispersal in Gunnison's prairie dogs (Cynomys gunnisoni)

Populations of the highly social Gunnison's prairie dog (Cynomys gunnisoni) were studied at two sites in south central Colorado. The sites differed in availability of water, duration of the growing season, and the diversity and quantity of edible vegetation. At the lusher site, Quartz Creek, all age- and sex classes weighed significantly more than their counterparts at the more barren site, Blue Mesa. Growth rates and overwinter survival of Quartz Creek young were higher than at Blue Mesa. Two of 5 yearling females raised litters at Quartz Creek, whereas none of 15 yearling females weaned litters at Blue Mesa. Quartz Creek females produced larger litters [Formula: see text] than Blue Mesa females [Formula: see text]. At Quartz Creek, 6 of 17 yearlings dispersed from their natal harem, but none of the 31 yearlings at Blue Mesa dispersed. Thus, in a favorable habitat, Gunnison's prairie dogs were heavier, reached sexual maturity more rapidly, and dispersed at a younger age than in a less favorable habitat. These results provide intraspecific support for Armitage's hypothesis that delayed sexual maturity and dispersal in the large-bodied, social ground squirrels is associated with the age at which immatures attain adult weight.

Dynamics of a Plague Outbreak in Gunnison's Prairie Dog

In the third year of my study of social behavior and population dynamics in the Gunnison's prairie dog (Cynomys gunnisoni), one colony was eliminated by sylvatic plague (Yersinia pestis). The passage of plague through prairie dog colonies has been reported previously (Eskey and Haas, 1940; Ecke and Johnson, 1952; Lechleitner et al., 1962, 1968), but only one other colony has been observed prior to the onset of a plague outbreak: Clark's (1977) study of white-tailed prairie dogs (Cynomys leucurus). The present report provides detailed population data prior to and during a plague outbreak in the Gunnison's prairie dog. I monitored a 3.4-ha study site west of Willow Creek, near Blue Mesa Reservoir in Curecanti National Recreation Area, Gunnison Co., Colorado (38'28'N, 107'06'W). The study site was within a 60-ha prairie dog colony, which was bounded by the reservoir, hills, and U.S. Highway 50. No burrows were found more than three meters up the hillside. Small subpopulations existed across the highway but expansion was limited by hills and ranches. The predominant plants in the colony were borages (Cryptantha fendleri, Lappula redowski), mustards (Lepidium virginicum, Cardaria draba, Descurainia sophia, Sisymbrium altissimum), and sagebrush (Artemisia spp.). I live-trapped prairie dogs almost daily in June through August during 1979 and 1980, and from 25 March to 16 April 1981. At the end of 1980, 194 animals were residents of the study area and an estimated 1000-1500 animals constituted the entire colony (Table 1). In 1981 prairie dogs began emerging from hibernation in early March, a month or two earlier than usual for the Gunnison River Valley (D. Hill, U.S. National Park Service Naturalist, pers. comm.). When I arrived at Willow Creek on 25 March, about 40 animals were active in the study site; this was fewer than anticipated three weeks after emergence. Within the Tribe Marmotini, males typically emerge before females (Michener, 1984), and male prairie dogs typically are more trappable than females; however, in 1981 I trapped disproportionately few males (Table 1). On 7 April 1981, I found a dead yearling female that had had an unusually large number of fleas on her body when trapped three days earlier. During normal handling procedures it is common to see several fleas on an animal, but hundreds of fleas had been hopping on this animal and on myself. On 11 and 12 April three more animals were found dead at their burrow entrances. Two had been trapped within the preceding two weeks. All three animals were sent to the Center for Disease Control (CDC), Plague Branch, in Fort Collins, Colorado, where they were diagnosed as having died of sylvatic plague caused by Yersinia pestis bacterium transmitted by the fleas Opisocrostis hirsutis and 0. tuberculatus cynomyris. Furthermore, every flea examined was highly infectious, making this one of the hottest plague outbreaks the CDC had seen (CDC, pers. comm.). As spring progressed, prairie dogs continued to die of plague shortly after emerging from hibernation. Known individuals were observed repeatedly, then disappeared. Newly emerged animals were active for about a week before disappearing. The scarcity of the earlier emerging males might have been due to the sequential effect of plague on emerging animals or to greater susceptibility of males to infection (as with rats, Kartman et al., 1962b). Although mortality rates of females and young were higher in Clark's (1977) study, his mortality data were confounded by the midsummer immergence of adult males. By 21 April only a single individual remained alive in the study site and only isolated, scattered groups were found elsewhere in the colony. By 25 April seven solitary individuals were distributed across the entire colony; four days later no survivors remained. Plague had exterminated the entire population of 1000-1500 individuals in less than two months. The rapid progress and high mortality of this plague outbreak are similar to the 85 percent mortality over 5 months in Clark's population of 62 white-tailed prairie dogs (Clark, 1977) and with the near 100 percent mortality reported by others (Ecke and Johnson, 1952; Lechleitner et al., 1962, 1968; Fitzgerald and Lechleitner, 1974). Because of the paucity of data on prairie dog or other ground squirrel populations prior to a plague outbreak, I have provided complete population data for the record. Population data from the study site are assumed to be representative of population growth in the colony overall (Table 1). In the 1979 field season all individuals of unknown age were considered to be adults; residents could not be distinguished from 194 Vol. 66, No. 1

Dialects in the alarm calls of prairie dogs

1. The alarm calls of the Gunnison's prairie dog, Cynomys gunnisoni zuniensis, have differentiated into local dialects. 2. Call characteristics show that, within a given dialect, the number of syllables, the length of the syllables, and the interval length between syllables are weakly correlated with one another. The number of syllables, however, is strongly correlated with the total length of the call. 3. Both the number of syllables and the total call length are strongly correlated with the complexity of the habitat: the more complex the habitat in terms of vegetation cover, rocks, and tree stumps, the more syllables there are and the longer is the call. This may be related to predation pressure, with prairie dogs in more complex habitats calling longer to warn their kin when a predator approaches.

Observations on the Biology of Gunnison's Prairie Dog in Central Colorado

A study was conducted from July 1965 to September 1966 on the biology of Gunnison's prairie dog (Cynomys gunnisoni gun- nisoni) in South Park, Park Co., Colorado. Prairie dogs within the colony were loosely organized into clans with adult females playing the major role in caring for the young and! warning of danger. Clan bound- aries were not patrolled or defended by clan members, but individual burrows, burrow systems or food supplies were protected by individual animals. Little aggression was observed within the clans but members of different clans would engage in disputes when they encountered each other in the common feeding areas. Females had a high ratio of suc- cessful pregnancies or uterine implantation sites, but mortality caused by a plague (Yersinia pestis) epizootic resulted in the extinction of the main study colony by the spring of 1967. Mean weights of adult males were significantly higher than weights of adult females. Weights of pups in- creased during the first summer so that by September a few individuals were as large as smaller adults. Immigration and emigration were not important in the colony and the only known successful predators were badgers and red-tailed hawks. Tactile, visual and vocal communication was important in the colony, but in general social behavior was not as well developed as in black-tailed prairie dogs. Prairie dogs were diur- nal with two periods of maximum surface activity. Gunnison's prairie dogs completely terminated surface activity for 7 months during the cold seasons of the year, with pups being the last animals to hibernate. Gun- nison's prairie dogs did not work or shape their mounds and their activ- ity had little visible impact on their environment. Most of the time the animals spent aboveground was occupied in eating or searching for food. Grasses were the preferred foods but a variety of forbs were also utilized.