Pronghorn Research Articles

Behavior and Activity Budgets of Sonoran Pronghorns (Antilocapra americana sonoriensis)

Abstract Sonoran pronghorns (Antilocapra americana sonoriensis) have been listed as endangered since 1967, yet relatively little is known about their behavior. Knowledge of behavior is essential to understanding their ecology, but these data are difficult to obtain for Sonoran pronghorns due to land-use restrictions and large, inaccessible range. However, with establishment of a semi-captive breeding facility (260 ha) for Sonoran pronghorns in southern Arizona, behavioral studies are feasible. We studied diurnal activity budgets of six adult female Sonoran pronghorns during January–December 2005 by recording behavior (i.e., foraging, bedding, standing, traveling, other) with instantaneous sampling at 2-min intervals. We observed pronghorns on 148 days during the year for a total of 49,035 observations. Pronghorns exhibited seasonal and diurnal differences in activity budgets. Behavior was constrained by temperature in spring and summer, and by availability of forage in autumn. These data are the first reg...

Arizona's Pronghorn Antelope: A Conservation Legacy. David E. Brown and Richard Ockenfels.

Arizona's Pronghorn Antelope: A Conservation Legacy. David E. Brown and Richard Ockenfels.

Ghosts Chasing Ghosts: Pronghorn and the Long Shadow of Evolution

Ghosts Chasing Ghosts: Pronghorn and the Long Shadow of Evolution

Toxic (Pb, Cd, Hg) and essential (Fe, Cu, Zn, Mn) metal content of liver tissue of some domestic and bush animals in Ghana

Accumulation of toxic metals in liver, a rich natural source of essential elements, can present health risks to regular consumers of liver. A total of 35 fresh liver samples of cow, sheep, goat, pig, grass-cutter (Thryonomys swinderianus), gaint rat (Cricetomys gambianus), red deer (Cervus elaphus), chicken and antelope (Antilocapra americana) were obtained from three different markets in Accra and Kumasi, Ghana. Samples were analyzed using atomic absorption spectrometry and an automatic mercury analyzer. Levels of iron in the grass-cutter and pig of 500.5–645.4 mg kg−1 were the highest in the animal livers examined. Mn concentrations were highest in grass-cutter and rat liver, ranging 16.5–30.2 mg kg−1. The safe Cu and Zn permissible limits of 20 and 50 mg kg−1 were exceeded in 70 and 75% of the liver samples, respectively. Generally, for each animal group studied, at least 50% of the sample livers exceeded the Cd permissible limit of 0.5 mg kg−1. The levels of Pb, which ranged 1.3–13.8 mg kg−1, exceeded the proposed European Commission (EC) limit of 0.5 mg kg−1. Care must be taken by regular consumers of the iron-rich animal livers of grass-cutter, pig and rat because they also had the highest levels of Pb (in grass-cutter and pig) and Cd (in grass-cutter, rat and pig). The liver samples analyzed for Hg had values far below the permissible limit of 0.5 mg kg−1.

Determinants of Survival and Fecundity Through a Population Bottleneck in Pronghorn (Antilocapra americana)

The long-term viability of small, isolated populations has been questioned in light of stochasticity and bottlenecks. Following a drought in northwestern Montana in 2003, the pronghorn (Antilocapra americana )o f the National Bison Range experienced a demographic bottleneck. We used information theoretic approaches to examine the influence of sex, age, genetic variation, summer lactation, mate-search effort by females, and mating effort by males on subsequent winter survival and spring fecundity. Survival of males was influenced by age, whereas survival of females was influenced by prior energy expenditure and genetic variation, implicating inbreeding depression as the mechanism. Fecundity of females also was influenced by prior energy expenditure and genetic variation, with heterosis as the apparent mechanism. Our results agree with those of other studies that have emphasized the need to maintain genetic variation and limit inbreeding in small, isolated populations, and to account for stochasticity in population viability assessments and long-term management planning.

Planning and Assessment of Activity Budget Studies Employing Instantaneous Sampling

AbstractTo obtain accurate estimates of activity budget parameters, samples must be unbiased and precise. Many researchers have considered how biased data may affect their ability to draw conclusions and examined ways to decrease bias in sampling efforts, but few have addressed the implications of not considering estimate precision. We propose a method to assess whether the number of instantaneous samples collected is sufficient to obtain precise activity budget parameter estimates. We draw on sampling theory to determine the number of observations per animal required to reach a desired bound on the error of estimation based on a stratified random sample, with individual animals acting as strata. We also discuss the optimal balance between the number of individuals sampled and the number of observations sampled per individual for a variety of sampling conditions. We present an empirical dataset on pronghorn (Antilocapra americana) as an example of the utility of the method. The required numbers of observation to reach precise estimates for pronghorn varied between common and rare behaviors, but precise estimates were achieved with <255 observations per individual for common behaviors. The two most apparent factors affecting the required number of observations for precise estimates were the number of individuals sampled and the complexity of the activity budget. This technique takes into account variation associated with individual activity budgets and population variation in activity budget parameter estimates, and helps to ensure that estimates are precise. The method can also be used for planning future sampling efforts.

Did climatic seasonality control late Quaternary artiodactyl densities in western North America?

We develop and test a hypothesis here that the seasonality of temperature and precipitation played a major role in determining the population densities of artiodactyls (e.g., Ovis canadensis, Odocoileus hemionus, and Antilocapra americana) across the terminal Pleistocene and Holocene of western North America. For much of this region, general circulation climate models and a range of paleoclimatic data suggest that seasonal extremes in temperature peaked during the terminal Pleistocene and early Holocene and that early and middle Holocene precipitation followed a winter-wet, summer-dry pattern—conditions known to depress artiodactyl densities. These trends are mirrored in a northern Bonneville Basin macrophysical climate simulation model from which we derive terminal Pleistocene and Holocene climatic values and three indices of climatic seasonality: (1) intra-annual temperature range, (2) summer precipitation intensity, and (3) winter precipitation intensity. These indices are arrayed against three detailed late Quaternary artiodactyl abundance records in the Bonneville Basin: a unique paleontological record of fecal pellet densities, and archaeological records of artiodactyl skeletal elements and large game hunting tools. Each of these artiodactyl abundance records shows significant correlations with the model-derived seasonality indices and suggests that artiodactyls occurred in low densities from the terminal Pleistocene through the middle Holocene—substantial increases occurred during equable, summer-wet periods of the late Holocene. Archaeological vertebrate records from across western North America show very similar temporal patterns in artiodactyl abundances suggesting that the trend and its climate-based causes may be a very general one. These conclusions have far-reaching implications not only for our understanding of ancient human hunting and land use patterns, but for the future management of artiodactyls under scenarios of global warming that also project dramatic increases in extreme climate.

Winter Precipitation and Recruitment Of Pronghorns In Arizona

Recruitment of pronghorns (Antilocapra americana; fawns∶100 females) through late summer was positively correlated with precipitation during the previous winter (October–April) on 10 areas in Arizona during 1983–2002. There was no evidence of serial autocorrelation in recruitment of fawns and no strong within-year effects, even after accounting for differences in winter precipitation among sites. There was no evidence that the relationship between winter precipitation and recruitment differed among populations. Winter precipitation explained 38.5% of variability in recruitment among years within populations. We hypothesize that winter precipitation is a limiting factor affecting recruitment in populations of pronghorns in arid and semi-arid habitats in Arizona.

Behavior and Timing Of Life-History Events In A Semi-Captive Population Of the Sonoran Pronghorn (Antilocapra americana sonoriensis)

The Sonoran pronghorn (Antilocapra americana sonoriensis) has been listed as endangered since 1967, yet little is known about its behavior due to difficulties observing them in the wild. During a study of Sonoran pronghorn in a semi-captive breeding facility in southern Arizona, we observed behaviors and timing of life-history events that have not been documented in peer-reviewed literature, including birth dates of fawns, pre-parturient and post-parturient behavior, timing of breeding season, behavior during the breeding season, date of horn casting by males, and response to predators. Behavior of the Sonoran pronghorn before and after parturition, during breeding, and toward predators was consistent with that reported for other subspecies. Timing of breeding, parturition, and horn casting all occurred earlier than reported for more northerly populations. Variation in timing of life-history activities was the main difference between the Sonoran pronghorn and other subspecies and would be expected due to the correspondence between seasonal rainfall and forage conditions in the Sonoran Desert and timing of parturition.

Yellowstone Pronghorn Alter Resource Selection After Sagebrush Decline

Animals alter resource use as conditions change and these changes could have significant consequences on demography. We generated a logistic resource selection probability function for habitat use and estimated percent composition of diets by pronghorn (Antilocapra americana) in Yellowstone National Park during winter to assess if selection of sagebrush (Artemisia) has changed since the 1960s, corresponding with diminishing sagebrush and increasing seral species such as rabbitbrush (Chrysothamnus). We located 37 radiocollared adult females in 1,440 different groups during December 1999 through March 2005 and compared habitat attributes to 9,347 randomly selected points from the winter range. Pronghorn preferred greasewood (Sarcobatus vermiculatus) and selected grasslands in comparison to the sagebrush cover type. The relative selection against sagebrush may stem from a substantial decrease in this plant type on the winter range by the 1960s due to intense browsing by congregated ungulates. The percent composition of sagebrush in the winter diets of pronghorn decreased from 67% during 1985–1988 to <10% during 2000–2001, while rabbitbrush increased from 5% to 60%. These findings and the results of companion time-series analyses suggest the winter range for Yellowstone pronghorn may not support larger populations (>500) of pronghorn for sustained periods, as occurred historically. Similar effects from habitat fragmentation and degradation face managers of migratory ungulates worldwide.

Thermoregulatory anatomy of pronghorn (Antilocapra americana)

We have found that pronghorn (Antilocapra americana) use external heat exchange with the environment and internal heat exchange between the carotid artery rete and cavernous venous sinus blood to regulate body temperature. Now we have investigated the relationship between the histological structure of the skin, cephalic veins, and carotid rete–cavernous sinus system and the physiological mechanisms pronghorn use, and whether their thermoregulatory anatomy has adaptive advantages. We harvested tissue samples of skin, three veins (i.e., angularis oculi vein, dorsal nasal vein, and facial vein), and the carotid rete–cavernous sinus system from four pronghorn, two culled in summer and two in winter, and examined each histologically. The three veins had the typical structure of veins with large lumina and thin walls. The carotid rete consisted of small (0.1–0.5 mm) arterioles with a density of ~10/mm2, intertwined with veins (~2/mm2), enclosed within the cavernous sinus; a structure ideal for heat exchange. We concluded that the main function of the dorsal nasal and facial veins is to return cold blood to the body to effect whole body cooling. The cavernous sinus is supplied with warm blood by the palatine veins in winter and cold blood by the deep facial veins in summer, an arrangement different to that in other ungulates, such as sheep, in which the angularis oculi vein supplies the cavernous sinus. Pronghorn skin is richly supplied with blood vessels that facilitate convective heat loss in summer. In winter, the number of coarse and fine hairs per square millimeter increases more than in European deer to form a thick pelage that minimizes heat loss. In summer, the pelage is shed because hair follicles involute. Unlike in other ungulates, pronghorn skin has little adipose tissue. The number of apocrine glands increases in winter rather than in summer. We concluded that the glands have a reproductive/social function rather than a thermoregulatory one. In summary, our study shows that the thermoregulatory anatomy is consistent with our physiological data and has adaptive advantages that help explain the survival of pronghorn in an arid habitat characterized by extreme temperature variation and sparse vegetation.

Visual Observation of Bobcat Predation on an Adult Female Pronghorn in Northwestern South Dakota

ABSTRACT Published reports of survival and cause-specific mortality for pronghorn (Antilocapra americana) indicate that mortality differs regionally and seasonally with sex, age and density of pronghorn. Cold winters with deep crusted snow is a primary source of mortality on adult pronghorn, however, predation also can be an important source of adult mortality. We report a visual observation of bobcat (Felis rufus) predation on an adult female pronghorn in northwestern South Dakota.

Protecting Migration Corridors: Challenges and Optimism for Mongolian Saiga

Migrations are an important ecological phenomena rapidly declining throughout the world [1]. Within many ungulate populations, migration is a polymorphic trait; animals can cover either long or short distances, pass across broad swaths of land such as those of caribou (Rangifer tarandus) and wildebeest (Connochaetes taurinus), or squeeze through bottlenecks as narrow as 120 meters as described for pronghorn (Antilocapra americana) [2,3]. Given that the persistence of terrestrial migration is challenged primarily by anthropogenic forces, protection is often possible, assuming the availability of appropriate knowledge concerning movements, threats, and meta-population structure, and the willingness to implement coincident conservation actions that involve local decision makers. Here, we illustrate these issues by profiling an endangered species—the Mongolian saiga (Saiga tatarica mongolica; Figure 1), highlighting the importance of protecting movement routes in light of habitat, human culture, and other sources of population risk. Figure 1 Mongolian Saiga (Saiga tatarica mongolica)

Possibility of Heat-Related Mortality in Desert Ungulates

Studies on mortality of young ungulates in arid environments usually restrict the possible causes of death to predation, starvation, or disease. However, hyperthermia as a cause of death in wild animals living in arid environments is rarely discussed or considered and might be a source of mortality in juveniles. During a two-week period after 11 July 2005, four Sonoran pronghorn (Antilocapra americana sonoriensis) fawns (4–5 months old) died of unknown causes in a 130-ha enclosure in southern Arizona. Predation did not appear to be the cause of death. Likewise, starvation does not appear to be the cause of death because fawns did not exhibit observable signs of malnutrition prior to the period of their death. Disease also appears to be unlikely because the timing of occurrence of the vector for the two main diseases known to occur in the population (i.e., blue tongue and epizootic hemorrhagic disease [EHD]) does not coincide with the fawn deaths (although this does not rule out other potential disease). Hyperthermia might have been the cause of death of the four fawns because the three hottest days of the year (44.1, 44.1, and 43.6 °C) occurred during the period the fawns died. While our evidence for hyperthermia as the cause of death is speculative, biologists should consider the possibility that young desert-dwelling ungulates may be susceptible to hyperthermia during the hottest period of the year and that it might be a source of fawn mortality that cannot be managed.

The American West’s longest large mammal migration: clarifying and securing the common interest

Over the last 10 years, conflict has grown over a 170-mile pronghorn antelope (Antilocapra americana) migration between Grand Teton National Park and the Upper Green River Basin in western Wyoming. Resolving conflict in the common interest is proving difficult. This movement is the longest mammal migration in the lower 48 states, spanning the jurisdiction of three federal agencies, three Wyoming counties, and over 40 private landowners. In addition, there are over ten non-governmental conservation organizations, two major state agencies, Wyoming’s executive office, and many citizens involved in the issue. There are three major problem definitions serving the beliefs of participants: the ecological-scientific (conservation biologists, environmentalists), local rights (local control, property rights), and cultural value (historic, western heritage) definitions. These definitions challenge the social and decision making processes of regional communities and government agencies. Underlying the problem of securing the common interest is the highly fragmented patterns of authority and control, misorganized arena(s), and parochial perspectives of many participants. Options promoted by participants can be loosely classified as top-down (government, expert driven) versus bottom-up (local, practice-based) approaches and reflect preferences for the distribution and uses of power and other values. Given the social and decision making context of this case, the bottom-up, practiced-based approach would likely best secure a common interest outcome.

RECOLONIZING WOLVES AND MESOPREDATOR SUPPRESSION OF COYOTES: IMPACTS ON PRONGHORN POPULATION DYNAMICS

Food web theory predicts that the loss of large carnivores may contribute to elevated predation rates and, hence, declining prey populations, through the process of mesopredator release. However, opportunities to test predictions of the mesopredator release hypothesis are rare, and the extent to which changes in predation rates influence prey population dynamics may not be clear due to a lack of demographic information on the prey population of interest. We utilized spatial and seasonal heterogeneity in wolf distribution and abundance to evaluate whether mesopredator release of coyotes (Canis latrans), resulting from the extirpation of wolves (Canis lupus) throughout much of the United States, contributes to high rates of neonatal mortality in ungulates. To test this hypothesis, we contrasted causes of mortality and survival rates of pronghorn (Antilocapra americana) neonates captured at wolf-free and wolf-abundant sites in western Wyoming, USA, between 2002 and 2004. We then used these data to parameterize stochastic population models to heuristically assess the impact of wolves on pronghorn population dynamics due to changes in neonatal survival. Coyote predation was the primary cause of mortality at all sites, but mortality due to coyotes was 34% lower in areas utilized by wolves (P < 0.001). Based on simulation modeling, the realized population growth rate was 0.92 based on fawn survival in the absence of wolves, and 1.06 at sites utilized by wolves. Thus, wolf restoration is predicted to shift the trajectory of the pronghorn population from a declining to an increasing trend. Our results suggest that reintroductions of large carnivores may influence biodiversity through effects on prey populations mediated by mesopredator suppression. In addition, our approach, which combines empirical data on the population of interest with information from other data sources, demonstrates the utility of using simulation modeling to more fully evaluate ecological theories by moving beyond estimating changes in vital rates to analyses of population-level impacts.

INDIRECT EFFECTS AND TRADITIONAL TROPHIC CASCADES: A TEST INVOLVING WOLVES, COYOTES, AND PRONGHORN

The traditional trophic cascades model is based on consumer resource interactions at each link in a food chain. However, trophic-level interactions, such as mesocarnivore release resulting from intraguild predation, may also be important mediators of cascades. From September 2001 to August 2004, we used spatial and seasonal heterogeneity in wolf distribution and abundance in the southern Greater Yellowstone Ecosystem to evaluate whether mesopredator release of coyotes (Canis latrans), resulting from the extirpation of wolves (Canis lupus), accounts for high rates of coyote predation on pronghorn (Antilocapra americana) fawns observed in some areas. Results of this ecological perturbation in wolf densities, coyote densities, and pronghorn neonatal survival at wolf-free and wolf-abundant sites support the existence of a species-level trophic cascade. That wolves precipitated a trophic cascade was evidenced by fawn survival rates that were four-fold higher at sites used by wolves. A negative correlation between coyote and wolf densities supports the hypothesis that interspecific interactions between the two species facilitated the difference in fawn survival. Whereas densities of resident coyotes were similar between wolf-free and wolf-abundant sites, the abundance of transient coyotes was significantly lower in areas used by wolves. Thus, differential effects of wolves on solitary coyotes may be an important mechanism by which wolves limit coyote densities. Our results support the hypothesis that mesopredator release of coyotes contributes to high rates of coyote predation on pronghorn fawns, and demonstrate the importance of alternative food web pathways in structuring the dynamics of terrestrial systems.

Thermoregulation in pronghorn antelope (Antilocapra americana,Ord) in winter

Conservation of energy is a prerequisite thermoregulatory strategy for survival in northern hemisphere winters. We have used thermistor/data logger assemblies to measure temperatures in the brain, carotid artery, jugular vein and abdominal cavity, in pronghorn antelope to determine their winter body temperature and to investigate whether the carotid rete has a survival role. Over the study period mean black globe and air temperature were -0.5+/-3.2 degrees C and -2.0+/-3.4 degrees C, respectively, and mean daytime solar radiation was approximately 186 W m(-2). Brain temperature (T(brain), 39.3+/-0.3 degrees C) was higher than carotid blood temperature (T(carotid), 38.5+/-0.4 degrees C), and higher than jugular temperature (T(jugular), 37.9+/-0.7 degrees C). Minimum T(brain) (38.5+/-0.4 degrees C) and T(carotid) (37.8+/-0.2 degrees C) in winter were higher than the minimum T(brain) (37.7+/-0.5 degrees C) and T(carotid) (36.4+/-0.8 degrees C) in summer that we have reported previously. Compared with summer, winter body temperature patterns were characterized by an absence of selective brain cooling (SBC), a higher range of T(brain), a range of T(carotid) that was significantly narrower (1.8 degrees C) than in summer (3.1 degrees C), and changes in T(carotid) and T(brain) that were more highly correlated (r=0.99 in winter vs r=0.83 in summer). These findings suggest that in winter the effects of the carotid rete are reduced, which eliminates SBC and prevents independent regulation of T(brain), thus coupling T(brain) to T(carotid). The net effect is that T(carotid) varies little. A possible consequence is depression of metabolism, with the survival advantage of conservation of energy. These findings also suggest that the carotid rete has wider thermoregulatory effects than its traditional SBC function.

Validation of an Anaplasma marginale cELISA for use in the diagnosis of A. ovis infections in domestic sheep and Anaplasma spp. in wild ungulates

A commercially available (cELISA) kit for diagnosing Anaplasma marginale infection in cattle was validated for diagnosing A ovis infection in sheep using the bovine serum controls as supplied by the manufacturer (BcELISA) and sheep serum controls from pathogen-free sheep (OcELISA). True positives were identified using two previously established assays, a nested PCR (nPCR) test and an indirect immunofluorescent assay (IFA). The BcELISA was also applied to sera from various species of wild ruminants, comparing the results with the IFA. Receiver operating characteristic (ROC) analysis indicated that the predicted threshold inhibition for the BcELISA was 19.2. The sensitivity for the BcELISA was 98.2% and the specificity was 96.3%. The predicted threshold inhibition decreased to 14.3 for the OcELISA; the sensitivity was 96.5% and the specificity was 98.1%. There was ≥90% concordance between IFA and nPCR, as well as between the BcELISA at 19% inhibition cutoff and either IFA or PCR. Concordance between the cELISA and IFA using sera from elk, mule deer, bighorn sheep, pronghorn antelope, and black-tailed deer ranged from 64% to 100%. This commercially available cELISA test kit can be used very effectively to test domestic sheep for infection with A. ovis using the kit-supplied controls (i.e. the BcELISA) and a 19% inhibition cutoff; the kit may also be useful for detecting intra-erythrocytic Anaplasma infections in wild ruminants.

Genetic Diversity and Gene Flow in Yellowstone Basin Pronghorn (Antilocapra Americana)

Yellowstone National Park's northern range is home to a geographically isolated population of pronghorn (Antilocapra americana) greatly reduced from historic levels of abundance. The genetic consequences of demographic declines in this population over the past 150 years are unknown, and the rates of genetic exchange among this and other populations in the Yellowstone basin are also unknown. We used 18 nuclear DNA microsatellite loci and noninvasively collected fecal samples from 73 individuals to quantify basic population genetic parameters and gene flow within and among the Yellowstone pronghorn population, a new population in the Paradise Valley, and a large population near Livingston, MT. Evidence for a genetic bottleneck in Yellowstone was strong based on several tests of heterozygote excess (Wilcoxon tests P≤ 0.033) and the relative ratio of allele richness to allele size range (M =0.283). However, mean population heterozygosity was high (HO = 0.665), and no indications of inbreeding were detected. Gene flow from elsewhere in the Yellowstone basin to Yellowstone National Park is extremely low. However, emigration from Yellowstone to the Paradise Valley population is high (26.7%), reinforcing conclusions based on behavioral data that this new population was founded by Yellowstone individuals. Despite years of population decline and genetic isolation, Yellowstone pronghorn appear to retain substantial genetic diversity.