Books & Contributions
Hoogland, J.L., editor. 2006. Conservation of the black-tailed prairie dog: saving North America’s western grasslands. Island Press, Washington, District of Columbia. [purchase]
Back Jacket. The prairie dog is a colonial, keystone species of the grassland ecosystem of western North America. Myriad animals regularly visit colony-sites to feed on the grass there, to use the burrows for shelter or nesting, or to prey on the prairie dogs. Unfortunately, prairie dogs are disappearing, and the current number is only about 2% of the number encountered by Lewis and Clark in the early 1800s. Part I of Conservation of the Black-Tailed Prairie Dog summarizes ecology and social behavior for pivotal issues such as when prairie dogs breed, how far they disperse, how they affect other organisms, and how much they compete with livestock. Part II documents how loss of habitat, poisoning, plague, and recreational shooting have caused the precipitous decline of prairie dog populations over the last 200 years. Part III proposes practical solutions that can ensure the longterm survival of the prairie dog and its grassland ecosystem, and also are fair to private landowners. We cannot expect farmers and ranchers to bear all the costs of conservation while the rest of us enjoy all the benefits. With 700 references, 37 tables, 75 figures and photographs, and a glossary, Conservation of the Black-Tailed Prairie Dog is a unique and vital contribution for wildlife managers, politicians, environmentalists, and curious naturalists.
Chapters Within. Hoogland, J. L. 2006. Why care about prairie dogs? Pages 1-4.
Hoogland, J. L. 2006. Natural history of prairie dogs. Pages 5-6.
Hoogland, J. L. 2006. Social behavior of prairie dogs. Pages 7-26.
Hoogland, J. L. 2006. Demography and population dynamics of prairie dogs. Pages 27-52.
Hoogland, J. L. 2006. Why have so many prairie dogs disappeared? Pages 89-93.
Hoogland, J . L. 2006. Saving prairie dogs: Can we? Should we? Pages 261-266.
Hoogland, J. L. 2006. Glossary of prairie dog terms. Pages 279-288.
Hoogland, J.L. 1996. Cynomys ludovicianus. Mammalian Species 535:1-10
Hoogland, J.L. 1995. The black-tailed prairie dog: Social life of a burrowing mammal. The University of Chicago Press, Chicago. [purchase]
Back Jacket. In The Black-Tailed Prairie Dog, John L. Hoogland draws on sixteen years of research at Wind Cave National Park, South Dakota, to provide the definitive account of prairie dog social behavior. Through comparisons with more than 300 other animal species, he offers new insights into basic theory in behavioral ecology and sociobiology. Hoogland documents interactions within and among families of prairie dogs to examine the advantages and disadvantages of coloniality. By addressing such topics as male and female reproductive success, inbreeding, kin recognition, and infanticide, Hoogland offers a broad view of conflict and cooperation. Among his surprising findings is that prairie dog females sometimes suckle, and at other times kill, the offspring of close kin. Enhanced by more than 100 photographs and useful summaries of data in tables and graphs, this book illuminates the social organization of a burrowing mammal and raises fundamental questions about current theory. As the most detailed long-term study of any social rodent, The Black-Tailed Prairie Dog will interest not only mammalogists and other vertebrate biologists, but also students of behavioral and evolutionary ecology in other taxa.
Manno, T.G., E.M. Bond (photography). 2014. The Utah prairie dog: life among the red rocks. The University of Utah Press, Salt Lake City. (foreword by John L. Hoogland) [purchase]
Back Jacket. A prairie dog town is a busy place. As author and field researcher Theodore Manno explains, a prairie dog's life can be full of mischief, romantic trysts, fighting, kissing, evading predators, and infanticide, which can all be witnessed over the course of a few months. In this definitive book on Utah prairie dogs, Manno vividly recounts the daily ups and downs of prairie dog life as well as his own trials and triumphs while observing these rare rodents in Bryce Canyong National Park. As part of John Hoogland's long-term study team, Manno and other members of the "Dog Squad" recorded the behavior of the "town" residents from the vantage point of a nine-foot-tall tower. Over time, the researchers came to know the personalities, family relationships, and social structure of the town's inhabitants. Demonstrating an unbridled passion for research, Manno communicates the satisfaction, excitement, and sadness that comes with watching marked individuals over time. His extensively researched narrative, accompanied by more than 150 photos by wildlife photographer Elaine Miller Bond, provides a full overview of what is currently known about Utah prairie dogs, a species that is threatened with extinction.
Invited Submissions
Magazine Features
Hoogland, J.L. 2017. Prairie dogs are charming and cute, but they are also serial killers. Scientia.
Peer-Reviewed Articles
Abstract. Fleas (Insecta: Siphonaptera) are hematophagous ectoparasites that can reduce the fitness of vertebrate hosts. Laboratory populations of fleas decline under dry conditions, implying that populations of fleas will also decline when precipitation is scarce under natural conditions. If precipitation and hence vegetative production are reduced, however, then herbivorous hosts might suffer declines in body condition and have weakened defenses against fleas, so that fleas will increase in abundance. We tested these competing hypotheses using information from 23 yr of research on 3 species of colonial prairie dogs in the western United States: Gunnison’s prairie dog (Cynomys gunnisoni, 1989–1994), Utah prairie dog (Cynomys parvidens, 1996–2005), and white-tailed prairie dog (Cynomys leucurus, 2006–2012). For all 3 species, flea-counts per individual varied inversely with the number of days in the prior growing season with .10 mm of precipitation, an index of the number of precipitation events that might have caused a substantial, prolonged increase in soil moisture and vegetative production. Flea-counts per Utah prairie dog also varied inversely with cumulative precipitation of the prior growing season. Furthermore, flea-counts per Gunnison’s and white-tailed prairie dog varied inversely with cumulative precipitation of the just-completed January and February. These results complement research on black-tailed prairie dog (Cynomys ludovicianus) and might have important ramifications for plague, a bacterial disease transmitted by fleas that devastates populations of prairie dogs. In particular, our results might help to explain why, at some colonies, epizootics of plague, which can kill .95% of prairie dogs, are more likely to occur during or shortly after periods of reduced precipitation. Climate change is projected to increase the frequency of droughts in the grasslands of western North America. If so, then climate change might affect the occurrence of plague epizootics among prairie dogs and other mammalian species that associate with them.
Abstract. Interspecific competition commonly selects for divergence in ecology, morphology or physiology, but direct observation of interspecific competition under natural conditions is difficult. Herbivorous white-tailed prairie dogs (Cynomys leucurus) employ an unusual strategy to reduce interspecific competition: they kill, but do not consume, herbivorous Wyoming ground squirrels (Urocitellus elegans) encountered in the prairie dog territories. Results from a 6-year study in Colorado, USA, revealed that interspecific killing of ground squirrels by prairie dogs was common, involving 47 different killers; 19 prairie dogs were serial killers in the same or consecutive years, and 30% of female prairie dogs killed at least one ground squirrel over their lifetimes. Females that killed ground squirrels had significantly higher annual and lifetime fitness than non-killers, probably because of decreased interspecific competition for vegetation. Our results document the first case of interspecific killing of competing individuals unrelated to predation (IK) among herbivorous mammals in the wild, and show that IK enhances fitness for animals living under natural conditions.
Abstract. Fleas (Insecta: Siphonaptera) are hematophagous ectoparasites that feed on vertebrate hosts. Fleas can reduce the fitness of hosts by interfering with immune responses, disrupting adaptive behaviors, and transmitting pathogens. The negative effects of fleas on hosts are usually most pronounced when fleas attain high densities. In lab studies, fleas desiccate and die under dry conditions, suggesting that populations of fleas will tend to decline when precipitation is scarce under natural conditions. To test this hypothesis, we compared precipitation vs. parasitism of black-tailed prairie dogs (Cynomys ludovicianus) by fleas at a single colony during May and June of 13 consecutive years (1976–1988) at Wind Cave National Park, South Dakota, USA. The number of fleas on prairie dogs decreased with increasing precipitation during both the prior growing season (April through August of the prior year) and the just-completed winter–spring (January through April of current year). Due to the reduction in available moisture and palatable forage in dry years, herbivorous prairie dogs might have been food-limited, with weakened behavioral and immunological defenses against fleas. In support of this hypothesis, adult prairie dogs of low mass harbored more fleas than heavier adults. Our results have implications for the spread of plague, an introduced bacterial disease, transmitted by fleas, that devastates prairie dog colonies and, in doing so, can transform grassland ecosystems.
Abstract. Vigilance is important for survivorship and reproductive success and is common and conspicuous within hundreds of species across a diverse array of taxa. Vigilance can involve either scanning for predators (antipredator vigilance) or watching conspecifics (social vigilance). From observations of marked Gunnison's prairie dogs, Cynomys gunnisoni (Sciuridae), living under natural conditions at Valles Caldera National Preserve, New Mexico, U.S.A., we compared results from the two most common sampling methods used by behavioural ecologists to measure vigilance: focal sampling (i.e. observing an individual for a specific amount of time and recording the amount of time spent vigilant) and scan sampling (i.e. observing all individuals in an area at a single moment and recording whether each individual at that moment is vigilant or nonvigilant). Information from different individuals and from the same individuals over time both revealed that estimates of vigilance from scan sampling were consistently and significantly higher than estimates from focal sampling. These differences probably resulted because nonvigilant behaviours were more difficult to detect in scan samples than in focal samples. Our results have important implications for behavioural ecologists who want to make intraspecific or interspecific comparisons of vigilance.
Abstract. A female usually obtains sufficient sperm to fertilize all her eggs from a single insemination, and mating can be costly. Yet, paradoxically, polyandry (i.e., copulation with 2 or more males) is common among organisms of all types, from amoebae through humans. Research that spanned 35 years shows that females of 3 species of prairie dogs benefited from polyandry by rearing more yearlings (a component of fitness that is my best estimate of female reproductive success); females of a 4th species (the black-tailed prairie dog [Cynomys ludovicianus]) evidently did not benefit from polyandry. Reasons for the higher production of yearlings by polyandrous females differed among species. For Gunnison’s prairie dogs (C. gunnisoni), 3 other components of fitness contributed to the higher production of yearlings: a higher probability of conception and parturition, larger litter size at weaning, and a higher survivorship of offspring during the first 9 months after weaning. The 2nd and 3rd components applied to Utah prairie dogs (C. parvidens), but only the 1st component applied to white-tailed prairie dogs (C. leucurus). Female Gunnison’s and white-tailed prairie dogs paid a cost from copulating with more than 1 male, because they were less likely to survive until the next mating season.
Abstract. Because competition decreases inclusive fitness among kin, Hamilton and May predicted that the presence of nearby kin should induce the dispersal of individuals from the natal territory, independent of pressures to avoid inbreeding. Many studies support this landmark prediction, but research over 31 years with prairie dogs reveals the opposite pattern: Young females are 12.5 times more likely to disperse in the absence of mother and siblings for one species, and 5.5 times more likely for another species. Such striking patterns probably occur because cooperation among kin is more important than competition among kin for young prairie dogs. The inability to cooperate with close kin, due to their absence, prompts a search for a new territory where cooperation might be less crucial for survival and reproduction.
Abstract. Vigilance for predators is omnipresent among species of prey. We report an investigation of vigilance of white-tailed prairie dogs (Sciuridae: Cynomys leucurus) living under natural conditions. Our most important conclusion concerns variation in vigilance within and among uniquely marked adult individuals (n=53 in 2007, n=62 in 2008). Within a single day, the percentage of observations when an individual was scanning for predators ranged from 0–100%, with a mean of 24.4%. Over a period of 3 months, some individuals were vigilant for <5% of observations, but others were vigilant for >50% of observations. For 12 of 24 individuals that we monitored for vigilance in consecutive years, levels of vigilance were significantly different between years. Some of the variation within and between individuals might have resulted from differences in vulnerability to predation.
Abstract. Gunnison’s prairie dogs (Cynomys gunnisoni) are rare, diurnal, colonial, burrowing, ground-dwelling squirrels. Studies of marked individuals living under natural conditions in the 1970s, 1980s, and 1990s showed that males are heavier than females throughout the year; that adult females living in the same territory are consistently close kin; and that females usually mate with the sexually mature male(s) living in the home territory. Research from 2007 through 2010 challenges all 3 of these findings. Here we discuss how different methods might have led to the discrepancies.
Abstract. From 1995 through 2005, I studied nursing among Utah prairie dogs (Cynomys parvidens) living under natural conditions at Bryce Canyon National Park, UT,
USA. I observed 850 aboveground nursings, which involved 122 mothers and 248 juveniles from 134 litters. Most of the mothers that nursed aboveground were middle aged,
and most nursing juveniles had been coming aboveground for 1–3 weeks. Most nursings involved a single juvenile, lasted 1–10 min, and occurred between 1800 hours
and 2000 hours. Seventy-five percent of nursings (598/796) involved a mother suckling her own juvenile offspring; the other 24.9% (198/796) involved a mother suckling another mother’s offspring (i.e., communal nursing). Communal nursings involved juveniles of the home territory, and many communal nursings (74/198=37.4%) involved close kin such as half-siblings, grand offspring, full-nieces, and full nephews; other communal nursings (37/198=18.7%) involved more distant kin such as full-second cousins and full-third cousins. Of seven hypotheses that might explain the evolution of communal nursing, evidence supports the importance of two: elevated inclusive fitness via indirect selection and communal nursing as a cost of coloniality.
Abstract. Using a long-term study of black-tailed prairie dogs (Cynomys ludovicianus), we asked whether subdivision of a subpopulation (colony) into social breeding groups coteries) influenced gene dynamics. We measured gene dynamics with common statistical tools, F-statistics and effective population size (Ne), but at a finer scale to account for coteries. We used 2 methods of estimating the gene dynamics of subgroups, and determined if these methods produced similar results that were congruent with an empirical measure of the observed effective population size (NeO). Modified F-statistics were estimated from pre- and postdispersal data from pedigrees and allozymes. Both indicated significant genetic substructuring of the colony subpopulation into coterie breeding groups. The rate of inbreeding of individuals relative to the coterie lineage indicated lower than expected inbreeding at the coterie level. Inbreeding of individuals relative to the colony was consistent with random mating. Asymptotic effective size estimates varied substantially. Chesser’s method produced estimates of 77 (range 69–90, pedigree) and 86 (range 70–111, allozyme) individuals consistent with the NeO of 76 and previous empirical estimates of the instantaneous asymptotic effective size from pedigrees (92.9). Nunney’s method produced much lower estimates of approximately one-half the NeO. Social subdivisions of the colony into coteries clearly influenced gene dynamics. Only the Chesser method accounted for genetic structure introduced by genealogy, both from polygynous mating and matrilines of philopatric females. This may prove important when estimating the rate of loss of genetic variation in highly social mammals.
Abstract. In recent years, people have interpreted scientific information about the black-tailed prairie dog (Cynomys ludovicianus) in various, and sometimes conflicting, ways. Political complexity around the relationship among black-tailed prairie dogs, agricultural interests, and wildlife has increased in recent years, particularly when prairie dogs occur on publicly owned lands leased to private entities for livestock grazing. Some have proposed that estimates of prairie dog (Cynomys spp.) numbers from 1900 are inflated, that prairie dog grazing is not unique (other grazers have similar affects on vegetation), and that prairie dogs significantly reduce carrying capacity for livestock and wildlife. We address all these issues but concentrate on the degree of competition between prairie dogs and ungulates because this motivates most prairie dog control actions. We conclude that the available information does not justify holding distribution and numbers of prairie dogs at a level that is too low to perform their keystone ecological function. We further conclude that it is especially important that prairie dogs be sufficiently abundant on public lands to perform this function.
Abstract. Social groups of philopatric female kin coupled with male-biased dispersal characterize many mammalian species. Such groups exhibit genetic properties, or gene dynamics (i.e., changes in genetic correlations), that potentially facilitate the evolution of group cohesion and cooperation. When groups fission, changes in gene dynamics occur that might affect cooperation. The distribution of females among coalitions newly formed via fission also may promote reproductive success by alleviating intraspecific competition. Families of black-tailed prairie dogs (Cynomys ludovicianus), called coteries, were observed during a 15-year study at Wind Cave National Park, South Dakota, and pedigrees of individuals were determined from livetrapping and electrophoretic analyses of paternity. We investigated the importance of coterie size, coterie density, and coancestry on the probability of fission; the effect of fissions on survivorship and territorial boundaries of coteries; and gene dynamics during and after fissions. Most new coteries occupied a subsection of the original territory. New coteries that contained a single female became extinct after about 1 year and their territories were usurped by adjacent coteries. Large coteries were more likely than smaller coteries to fission, but female coancestry within coteries usually did not influence the likelihood of fission, or the individuals that banded together in new groups. Members of new coteries interacted hostilely in the year after fission, but 1 or 2 generations elapsed before the new coteries became genetically distinct. We conclude that fission is probably driven by intraspecific competition within coteries rather than coancestry, and that coancestry does not explain the abrupt cessation of cooperation between individuals of the new coteries that result from fission.
Abstract. Predation always affects demography and population dynamics, but removal of certain types of individuals is especially consequential. Predators strike quickly and commonly avoid areas with human observers, however, and thereby make it difficult to document patterns of predation under natural conditions. At a colony of marked Utah prairie dogs (Cynomys parvidens), a high frequency of predation in 2005 provided an unusual opportunity to examine susceptibility of five types of individuals to predation by red foxes (Vulpes vulpes) and northern goshawks (Accipiter gentilis). Juveniles were more vulnerable than adults to predation by northern goshawks. Adults at the edge of the colony were more vulnerable than central adults to predation by both red foxes and northern goshawks. Recent immigrants, who were not yet familiar with the best routes for escape, were more likely than longtime residents to be captured by northern goshawks. Adult males, preoccupied with finding, impregnating, and guarding estrous females during the 17-day mating season, were easy targets for red foxes and northern goshawks. Pregnant females, who could not run quickly, were especially prone to predation by red foxes.
Abstract. Plague is an introduced bacterial disease whose primary vectors are fleas (Siphonaptera). Utah prairie dogs (Cynomys parvidens) are highly susceptible to plague, and entire colonies usually disappear shortly after plague arrives. Infusion of burrows with Pyraperm (an insecticidedust) kills fleas and immediately halts the spread of plague within colonies. Thus, insecticide-dusts might play an important role in the conservation of prairie dogs.
Abstract. Effective population sizes reported in the literature typically range from a small fraction of the adult population to about half the number of breeding adults. Theoretically, however, social structuring of genetic diversity could produce effective sizes as great as or even greater than population size. A colony of the highly social black-tailed prairie dog (Cynomys ludovicianus) was studied in the field for 16 years, and data were gathered for estimation of effective population sizes from pedigrees, demography, and allozyme alleles. Social breeding groups (‘‘coteries’’) within the colony exhibited high correlations of genes among individuals, and different coteries exhibited substantial genetic differentiation. Genetic diversity thus occurred within individuals, within coteries, and among coteries, and shifted among these levels of organization over time. ‘‘Instantaneous’’ estimates of effective size from short-term (annual) changes in genetic correlations were calculated from pedigree information but were not useful because they produced a wide diversity of estimates, due in part to the lack of demographic and genetic equilibrium in the colony. ‘‘Asymptotic’’ measures of effective population size that assumed eventual genetic equilibrium yielded relatively consistent estimates of effective sizes. For 10 years of empirical results from prairie dogs, effective population sizes from pedigrees (harmonic mean ¼ 79.4), demographic model based on breeding groups (asymptote ¼ 88.5), and allozyme data (harmonic mean ¼ 88.9) were similar, and all were somewhat higher than the number of adults in the population (harmonic mean ¼ 74.1). The colony of prairie dogs, therefore, exhibited a lower rate of loss of genetic diversity than expected, due to the genetic substructure created by the presence of social breeding groups.
Abstract. Feasibility of assigning parentage using variable microsatellite loci was assessed for 2 species of prairie dogs. Parentage was determined from 7 microsatellite loci for 46% of juveniles born during 1994 in a colony of Gunnison’s prairie dogs (Cynomys gunnisoni), and for 53% and for 45% of juveniles born during 1996 and 1997, respectively, in a colony of Utah prairie dogs (C. parvidens). Frequency of multiple paternity estimated for Gunnison’s (77%) and Utah (71% and 90%) prairie dogs was greater than that detected previously for black-tailed prairie dogs (5%–10%) but within the range reported for other grounddwelling squirrels. Of the 84 adult females and 33 adult males present during 1994 in the colony of Gunnison’s prairie dogs, 75 (89%) and 22 (67%), respectively, produced weaned offspring. Breeding success for Utah prairie dogs was relatively low in 1996 (45% for females and 32% for males) but increased in 1997 (80% for females and 81% for males).
Hoogland, J.L. 2003. Sexual dimorphism of prairie dogs. Journal of Mammalogy 84(4):1254-1266.
Abstract. Body mass is sexually dimorphic and varies seasonally for all 5 species of prairie dogs (Sciuridae: Cynomys), as shown by data from live individuals over a period of 28 years (1974–2001; n 5 16,447 body masses). Sexual dimorphism (i.e., body mass of males as percentage of body mass of females) during the breeding season is 105% for black-tailed prairie dogs, 127% for Utah prairie dogs, 131% for Gunnison’s prairie dogs, and 136% for white-tailed prairie dogs. Sexual dimorphism is minimal at the end of the breeding season, when exhausted males are thin and early-breeding females are heavy with pregnancy. Sexual dimorphism is maximal at weaning, when rested, well-fed males are heavy and females are emaciated from lactation. The most likely ultimate causation for sexual dimorphism among prairie dogs is sexual selection.
Abstract. Long-term research with marked individuals shows that black-tailed, Gunnison’s, and Utah prairie dogs (Sciuridae: Cynomys ludovicianus, C. gunnisoni, and C. parvidens) all reproduce slowly, despite claims of ranchers and early naturalists. Five factors are responsible for the slow reproduction. First, survivorship in the 1st year is 60% for all 3 species, and it remains low in later years. Second, even under optimal conditions, females of all 3 species produce only 1 litter/year. Third, the percentage of males that copulate as yearlings is only 6%, 24%, and 49% for black-tailed, Gunnison’s, and Utah prairie dogs, respectively. The percentage of females that copulate as yearlings is only 35% for black-tailed prairie dogs, but it is 100% for both Gunnison’s and Utah prairie dogs. Fourth, the probability of weaning a litter each year is only 43%, 82%, and 67% for female black-tailed, Gunnison’s, and Utah prairie dogs, respectively. Fifth, for those females that wean offspring, mean litter size at 1st juvenile emergence from the nursery burrow is 3.08, 3.77, and 3.88 for black-tailed, Gunnison’s, and Utah prairie dogs, respectively.
Introduction. Stapp (1998) recently argued that it was premature to characterize prairie dogs (Cynomys spp.) as keystone species. In particular, Stapp directed much of his criticism at a paper some of us wrote (Miller et al. 1994). He mistakenly interprets the main objective of our paper as providing evidence that prairie dogs are keystone species. Rather, the purpose of that paper was to outline an integrated strategy for conserving prairie dogs, and the theme was legal protection, habitat preservation, education, and economic incentives. It was presented in the context of prairie dog management policies having reduced grassland diversity. A discussion of the effect of prairie dogs on the ecosystem was, therefore, limited largely to an introductory paragraph. In this comment we address levels of knowledge about prairie dogs and prairie dogs as a keystone species.
Abstract. I examined dispersal and social organization of Gunnison's prairie dogs (Cynomys gunnisoni) for 7 years at Petrified Forest National Park, Arizona. Within colonies, individuals lived in harem-polygynous family groups called clans. The number of clans at the study site each year ranged from 21 to 23, with a mean of 22.3. Clan size (the number of adults living in the same territory) ranged from 1 to 19, with a mean of 5.30. Clans contained 1.06 ± 0.39 (SD) breeding males, 3.01 ± 2.08 breeding females, and 1.23 ± 1.65 nonbreeding yearling males. Some clans contained two breeding males, and others contained no resident breeding male. The area of clan territories ranged from 0.16 ha to 1.82 ha, with a mean of 0.67 ha. Females were more likely than males to copulate as yearlings (100% versus 24%). Ninety-five percent of females (340/358) remained in the natal clan territory for life, but only 5% of males (3/66) remained in the natal clan territory for> 1 year after weaning. Dispersal of both sexes was most commonly to an adjacent clan territory. Infanticide at the study colony was rare or absent.
Abstract. 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.
Abstract. 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.
Abstract. Genetic substructuring of a colony of black-tailed prairie dogs (Cynomys ludovicianus) was examined using three different sources of information: allozyme alleles, pedigrees, and demography (a "breeding-group" model based on mating and dispersal patterns). Prairie dogs and their social breeding groups (called "coteries") were studied under natural conditions during a 15-year period. Prairie-dog coteries exhibited substantial genetic differentiation, with 15-20% of the genetic variation occurring among coteries. Mating patterns within the colony approximated random mating, and, thus, mates tended to originate from different coteries. Social groups of black-tailed prairie dogs resulted in genetic substructuring of the colony, a conclusion that was supported by estimates from allozyme alleles and colony pedigrees. Predictions of the breeding-group model also were consistent with and supported by estimates from allozyme and pedigree data. Some methodological problems were revealed during analyses. Although individuals of all ages usually are pooled for biochemical estimates of among-group genetic differentiation, our estimates of among coterie variation from allozyme data were somewhat higher for young than for older prairie dogs, perhaps due to sampling effects caused by mating patterns and infanticide of offspring. Pedigree estimates of among-coterie genetic differentiation were significantly positive for young prairie dogs, adult females, and adult males. Those estimates were always more accurate for the offspring generation, however, because pedigree data were always more complete for young and genetic differences among coteries were diluted by virtually complete dispersal of males away from their natal coteries.
Abstract. 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 SD duration between parturition and the first emergence of juveniles from the natal burrow, is 38.6 2: 2.08 days (n ~ 112).
Abstract. Considerable controversy surrounds the importance of inbreeding in natural populations. The rate of natural inbreeding and the influences of behavioral mechanisms that serve to promote or minimize inbreeding (e.g., philopatry vs. dispersal) are poorly understood. We studied inbreeding and social structuring of a population of black-tailed prairie dogs (Cynomys ludovicianus) to assess the influence of dispersal and mating behavior on patterns of genetic variation. We examined 15 years of data on prairie dogs, including survival and reproduction, social behavior, pedigrees, and allozyme alleles. Pedigrees revealed mean inbreeding coefficients (F) of 1–2%. A breeding-group model that incorporated details of prairie dog behavior and demography was used to estimate values of fixation indices (F-statistics). Model predictions were consistent with the minimization of inbreeding within breeding groups (“coteries,” asymptotic FIL = –0.18) and random mating within the subpopulation (“colony,” asymptotic FIS = 0.00). Estimates from pedigrees (mean FIL = –0.23, mean FIS = 0.00) and allozyme data (mean FIL = –0.21, mean FIS = –0.01) were consistent with predictions of the model. The breeding-group model, pedigrees, and allozyme data showed remarkably congruent results, and indicated strong genetic structuring within the colony (FLS = 0.16, 0.19, and 0.17, respectively). We concluded that although inbreeding occurred in the colony, the rate of inbreeding was strongly minimized at the level of breeding groups, but not at the subpopulation level. The behavioral mechanisms most important to the minimization of inbreeding appeared to be patterns of male-biased dispersal of both subadults and adults, associated with strong philopatry of females. Incest avoidance also occurred, associated with recognition of close kin via direct social learning within the breeding groups.
Abstract. 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.
Introduction. Populations are often composed of more than just randomly mating subpopulations - many organisms form social groups with distinct patterns of mating and dispersal. Such patterns have received much attention in behavioral ecology, yet theories of population genetics rarely take social structures into account. Consequently, population geneticists often report high levels of apparent inbreeding and concomitantly low effective sizes, even for species that avoid mating between close kin. Recently, a view of gene dynamics has been introduced that takes dispersal and social structure into account. Accounting for social structure in population genetics leads to a different perspective on how genetic variation is partitioned and the rate at which genie diversity is lost in natural populations - a view that is more consistent with observed behaviors for the minimization of inbreeding.
Abstract. Because inbreeding and outbreeding both involve distinct benefits, some optimal level of inbreeding-outbreeding should result under natural conditions. Testing this hypothesis has been difficult, mainly because the detailed pedigrees necessary for defining levels of inbreeding have been unavailable for animals other than humans. A 14-yr study of black-tailed prairie dogs (Cynomys ludovicianus) has shown that individuals avoid extreme inbreeding with close kin such as parents, offspring, and full and half siblings, but they regularly inbreed with more distant kin such as full and half first cousins, full and half first cousins once removed, full and half second cousins, and so on. Previous research with other wild animals has not documented such a high frequency of moderate inbreeding. An examination of five measures of reproductive success failed to reveal inbreeding depression.
Abstract. Within a natural population of blacktailed prairie dogs (Cynomys ludovicianus), 68% of sampled juveniles received milk from foster mothers via communal nursing. In proximate terms, communal nursing may result because prairie dog mothers seem unable to discriminate between their own and others' offspring. In ultimate terms, both indirect selection and reduced predation on juveniles resulting from the formation of multilitter groupings have probably been important in the evolution of communal nursing.
In this paper. The present study was conducted to determine if juvenile weight was associated with litter size, sex, and juvenile or maternal heterozygosity in the black-tailed prairie dog (Cynomys ludovicianus). Several reports on genetic variation (Chesser, 1983; Foltz and Hoogland, 1983) have been published recently for C. ludovicianus, but the effect of heterozygosity on juvenile weight has not been investigated previously in this species.
Abstract. For the last 14 years, we have been studying the sociobiology, demography, and population dynamics of blacktailed prairie dogs (Cynomys ludovicianus) in Wind Cave National Park, South Dakota. Our study colony covers 6.6 hectares (16 acres) and has not expanded during the period of research; in late spring of each year the colony contains a mean ± SD of 133 ± 29 adults and yearlings and 81 ± 33 juveniles. We have discovered four surprising aspects of the demography and populations dynamics of prairie dogs. (1) Mortality during the first year is approximately 50% for both sexes. Those males that survive the first year can live as long as 5 years, and females that survive the first year can live as long as 7 years. (2) Litter size ranges from 1 to 6, the mean + SD is 3.05 + 1.08, and the mode is 3. (3) Although individuals of both sexes usually defer first breeding until the second year, 9% of females and 3% of males first produce offspring as yearlings. (4) Infanticide is the major source of juvenile mortality, accounting for the partial or total demise of 51% of all litters born. In the most common type of infanticide, lactating females kill the unweaned offspring of their sisters and daughters.
Abstract. Behavioural interactions among black-tailed prairie dogs (Cynomys ludovicianus) of the same sex clearly show nepotism (the favouring of kin). Males and females consistently interact more amicably with kin than with non-kin . Nepotism in this context is striking for two reasons . First, individuals do not interact more amicably with close kin such as offspring and full-siblings than with more distant kin such as half-siblings, full-nieces, half-nieces, and half-nephews . Second, nepotism varies inversely and dramatically with changes in competition for either oestrous females (among males) or nesting burrows and breeding rights (among females).
Abstract. A colony of black-tailed prairie dogs (Rodentia : Sciuridae : Cynomys ludovicianus) is subdivided into harem-polygynous social groups called coteries. The resident male(s) of each coterie often gives a unique mating call before or after copulating. Data on mating calls were available for 367 copulations. Males of one-male coteries were significantly more likely to call than males of multi-male coteries. In cases where a female copulated with more than one male, the first copulating male was significantly more likely to call than subsequent copulating males. A mating call given by the first copulating male did not deter the oestrous female from copulating with additional males . Coterie size varied inversely with calling. Surprisingly, females that copulated with a calling male were significantly less likely to wean a litter.
Abstract. Barn swallows (Hirundo rustica) often nest solitarily and are ecologically similar to colonially nesting cliff swallows (H. pyrrhonota). Northern rough-winged swallows (Stelgidopteryx serripennis) also nest solitarily and are ecologically similar to colonially nesting bank swallows (Riparia riparia). We investigated risk-taking in the mobbing of predators for these four species of North American swallows. We presented model owl and weasel predators and examined tendencies of individuals to dive at these predators during mobbing. Individuals of the two solitary species were significantly more likely to dive at predators than were individuals of the two colonial species. Since diving may be risky, we suggest that solitary species take greater per capita risks in mobbing than do colonial species. The reduced risk of falling victim during mobbing may be a benefit of group living that is perhaps independent of the effectiveness of mobbing.
Abstract. Infanticide, although common in a wide range of species including humans and other primates, is poorly understood. A 7-year study under natural conditions reveals that infanticide within colonies of black-tailed prairie dogs (Cynomys ludovicianus) is striking for three reasons. It is the major source of juvenile mortality, accounting for the total or partial demise of 51 percent of all litters born. The most common killers are resident lactating females. The most common victims are the offspring of close kin.
Abstract. At a colony containing 200 individuals of known ages and genetic relationships, I investigated alarm calling by black-tailed prairie dogs (Rodentia: Sciuridae: Cynomys ludovicianus) during experiments with a stuffed specimen of a natural predator, the badger (Taxidea taxus). As in other species of burrowing squirrels, female alarm calls are evidently nepotistic (i,e. function to warn genetic relatives). Male alarm calls are also nepotistic, and individual males vary their rate of alarm calling in response to the presence or absence of close genetic relatives in the home territory. Beneficiaries of alarm calls in other species of squirrels usually include adult or juvenile offspring, but beneficiaries of black-tailed prairie dog alarm calls frequently include only non-descendant kin.
In this paper. In this paper, we calculate two measures of population structure: Wright's (1978) genotype fixation index, F/s, and Allen's (1965) coefficient of nonrandom mating, Fn . The mean fixation index is negative in each year of the study, indicating an overall excess of heterozygotes. The coefficient of nonrandom mating is also negative each year, indicating an avoidance of consanguineous matings. This result is consistent with previous behavioral research on this species (Hoogland, 1982). We conclude that the mating pattern can explain some, but not all, of the heterozygote excess.
Response to. Michener, G.R., J.0. Murie. 1983. Black-tailed prairie dog coteries: Are they cooperatively breeding units? Am. Nat. 121:266-274.
Hoogland J.L. 1982. Prairie dogs avoid extreme inbreeding. Science 215(4540):1639-1641
Abstract. Black-tailed prairie dogs (Rodentia: Sciuridae: Cynomys ludovicianus) live in colonies composed of contiguous but separate family groups called coteries. During the 6 years that individuals in a colony were observed, they almost never mated with close genetic relatives. Inbreeding is avoided in four ways: (i) a young male usually leaves his natal coterie before breeding, but his female relatives remain; (ii) an adult male usually leaves his breeding coterie before his daughters mature; (iii) a young female is less likely to come into estrus if her father is in her coterie; and (iv) an estrous female behaviorally avoids mating with a father, son, or brother in her coterie.
Summary. Black-tailed prairie dogs are colonial rodents that live in contiguous social groups called coteries. A typical coterie contains one adult (> 2 years old) male, three or four adult females, and several yearlings and juveniles of both sexes. A large coterie sometimes contains two or more adult males. Using detailed behavioral observations on 164 females (of which 160 copulated) and data from four polymorphic loci from parents and offspring of 121 litters, we examined the black-tail mating system. Most females (101/164 = 62%) copulated with a single adult male, and only 3 of the 102 litters with >2 offspring (3%) showed unequivocal evidence of multiple paternity. Adult males usually copulated with several different adult females. In one-male coteries, females usually copulated exclusively with the resident adult male (RAM) (82/112= 73%); this trend was confirmed by electrophoresis of blood samples. In multimale coteries, each female frequently copulated with at least two different RAMs (28/52 = 54%); in 4 of 5 multimale coteries (80%) which produced two or more litters whose paternities could be unequivocally resolved by electrophoresis, two different RAMs each sired at least one litter. Of the 164 females, 30 (18%) copulated with both the RAM (or one of the RAMs, in multimale coteries) and an extracoterie adult male, but only 3 (2%) copulated exclusively with an extracoterie adult male. Electrophoresis showed that 9 of 121 litters (7%) were sired by an extracoterie adult male. Intersexual comparisons of annual reproductive success and lifetime reproductive success both indicate that black-tails are polygynous (i.e., that variance in reproductive success is greater for males than for females).
Abstract. Two colonies of black-tailed prairie dogs (Cynomys ludovicianus) in Wind Cave National Park, South Dakota, were compared during 1979 and 1980 to investigate the effects of (1) the age of the population and (2) the availability of resources on specific demographic parameters. The younger colony was surrounded by, and expanding into, unused available habitat. The older colony had little available habitat for expansion. At the younger colony (1) there was a greater proportion of successful pregnancies; (2) the litters were larger; (3) the juveniles grew faster; (4) yearlings were more likely to reproduce; (5) survivorship of adults and juveniles was greater, and (6) the density was more than 2x that of the older colony. Individuals at the younger colony showed a distinct feeding preference for vegetation growing at the colony periphery. Because this peripheral vegetation had only recently been modified from surplus habitat, we hypothesize that surplus habitat available to the younger colony accounted for the observed demographic differences.
Response to. Clark, A.B. 1978. Sex ratio and local resource competition in a prosimian primate. Science 201:163-165.
Abstract. In a 6-yr study, I investigated possible selective bases for coloniality in two species of squirrels (Sciuridae): loosely colonial White-tailed Prairie Dogs (Cynomys leucurus) and densely colonial Black-tailed Prairie Dogs (C. ludovicianus). White-tail study sites were in Wyoming and Colorado, USA; Black-tail study sites were in Colorado and South Dakota. I examined three hypotheses that might explain the evolution of coloniality: (a) shortage of suitable habitat, (b) social facilitation of foraging, and (c) reduced predation. The apparent surplus of unused suitable habitat and the absence of isolated individuals both indicated that prairie dogs are not forced to live together because of habitat shortages. An analysis of prairie dog foraging patterns indicated that there is no social facilitation of foraging in terms of either (a) group hunting of either large or elusive prey, (b) the location of large, scattered food supplies, (c) modification of the soil in order to effect the growth of vegetation that is more favorable or more abundant than that which would otherwise result, or (d) group defense of foraging grounds. Three lines of evidence indicate that reduced predation may be the most important benefit of prairie dog coloniality. First, simulated predatory attacks by badgers (Taxidea taxus) indicated that individuals in large wards (subcolonies) detect predators more quickly than do individuals in smaller wards; further, Black-tails detect predators more quickly than do White- tails. Second, individuals in large wards devote proportionately less time to alertness (i.e., scanning for predators) than do individuals in smaller wards, and Black-tails are less vigilant than are White-tails. Third, breeding synchronization and center-edge differences in individual alertness both indicate the possible importance of selfish herd effects. Interspecific differences in ward size and ward density may ultimately result because White-tail habitats contain significantly more protective cover than do Black-tail habitats.
Abstract. Black-tailed prairie dogs (Cynomys ludovicianus) live in colonies composed of contiguous but separate groups called coteries. A coterie usually contains one or two adult males, one to six adult females, and several yearlings and juveniles. For 50 of 52 litters produced by 46 females in 1979 and 1980, an electrophoretic analysis of four blood proteins indicated that the litter was fathered by one of the males in the home coterie. For 14 of 18 litters produced in coteries containing more than one adult male, paternity could be unambiguously assigned to one of the resident males. These results indicate that coteries, originally defined as units of social structure, are also units of reproduction.
Abstract. From 1974 to 1976, I examined individual alertness of two species of squirrels (Sciuridae): loosely colonial white-tailed prairie dogs (Cynomys leucurus) and densely colonial black-tailed prairie dogs (C. ludovicianus). By observing single adults for 30-min periods and recording various measures of alertness, I investigated the effects on individual alertness of four variables, all of which are directly related to ward (subcolony) size and ward density. Conclusions were based on data from 188 white-tail observations and 280 black-tail observations. Individual alertness consistently correlated negatively with effective increases in ward size and ward density. I discuss various hypotheses that might explain these negative correlations, and conclude that decreased individual alertness is an important benefit of prairie dog coloniality.
Introduction. There are no automatic or universal benefits of coloniality. Two costs of coloniality, however, are probably inevitable: increased competition (for food, mates, nest sites, etc.) and increased transmission of diseases and ectoparasites (Alexander, 1974). Other possible costs that are not automatic include increased probability of misdirected parental care resulting from either mixing of unrelated young, cuckoldry, or intraspecific brood parasitism; increased conspicuousness and increased attractiveness to predators; increased probability of indirect, deleterious consequences of nearby conspecific activity; and increased probability of having offspring killed or maimed by marauding conspecifics (Hoogland & Sherman, 1976).
Abstract. We studied the advantages and disadvantages of Bank Swallow (Riparia riparia) coloniality in 1972 and 1973 by examining 54 colonies, ranging in size from 2 to 451 active nests, near Ann Arbor, Michigan USA. Four disadvantages were investigated: (1) increased competition for nest burrows and nest building materials, (2) increased competition for mates and matings, (3) increased possibilities of misdirected parental care because of either brood parasitism or the mixing up of unrelated young, and (4) increased transmission of ectoparasites. Physical interference in reproductive functions and the possibility of intraspecific killing of offspring were also considered. The intensity of the various forms of competition increased with increasing colony size, though not always directly. Flea infestation also increased with increasing colony size. Intraspecific brood parasitism was not observed, and parent Bank Swallows began discriminating between their own and unrelated offspring at the time when the young first began to mix. Three hypotheses to explain the maintenance of coloniality were tested: (1) shortage of suitable nesting habitats, (2) advantages associated with social foraging, and (3) reduced predation on adults, young, or eggs. Shortage of suitable habitat could not be demonstrated. Parents did not appear to feed in groups, and survivorship of nestlings during cold weather and weight of nestlings at 10 days of age both suggested that competition for food increased with increasing colony size. Although there was no relationship between colony size and amount of nocturnal predation, adult birds mobbed diurnal predators. Using a stuffed weasel, we studied such mobbing responses. Our data suggest that diurnal predators at larger colonies are (1) detected more quickly, (2) mobbed by greater numbers of birds, and (3) subjected to more vocal commotion than are predators at smaller colonies. Further, we demonstrated that mobbing is at least sometimes effective in deterring avian predators. We suggest that reduced predation on eggs and young, resulting from both group defense and "selfish herd" effects, is an important advantage of Bank Swallow coloniality.