Hart Mountain National Antelope Refuge Research Articles

Application of Empirical Land-Cover Changes to Construct Climate Change Scenarios in Federally Managed Lands

Sagebrush-dominant ecosystems in the western United States are highly vulnerable to climatic variability. To understand how these ecosystems will respond under potential future conditions, we correlated changes in National Land Cover Dataset “Back-in-Time” fractional cover maps from 1985-2018 with Daymet climate data in three federally managed preserves in the sagebrush steppe ecosystem: Beaty Butte Herd Management Area, Hart Mountain National Antelope Refuge, and Sheldon National Wildlife Refuge. Future (2018 to 2050) abundance and distribution of vegetation cover were modeled at a 300-m resolution under a business-as-usual climate (BAU) scenario and a Representative Concentration Pathway (RCP) 8.5 climate change scenario. Spatially explicit map projections suggest that climate influences may make the landscape more homogeneous in the near future. Specifically, projections indicate that pixels with high bare ground cover become less bare ground dominant, pixels with moderate herbaceous cover contain less herbaceous cover, and pixels with low shrub cover contain more shrub cover. General vegetation patterns and composition do not differ dramatically between scenarios despite RCP 8.5 projections of +1.2 °C mean annual minimum temperatures and +7.6 mm total annual precipitation. Hart Mountain National Antelope Refuge is forecast to undergo the most change, with both models projecting larger declines in bare ground and larger increases in average herbaceous and shrub cover compared to Beaty Butte Herd Management Area and Sheldon National Wildlife Refuge. These scenarios present plausible future outcomes intended to guide federal land managers to identify vegetation cover changes that may affect habitat condition and availability for species of interest.

Long-Term Effects of Fire on Vegetation Structure and Predicted Fire Behavior in Wyoming Big Sagebrush Ecosystems

Fire historically occurred across the sagebrush steppe, but little is known about how patterns of post-fire fuel accumulation influence future fire in Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) communities. To quantify change in fuel composition and structure in intact sagebrush ecosystems, we sampled 17 years following prescribed fire in eight approximately 400 ha plots (4 burned, 4 unburned control) at Hart Mountain National Antelope Refuge, OR, USA. Fuels data were used to model potential fire behavior in burn and control plots across four environmental scenarios that mimic drying of fuels through the fire season. Seventeen years after fire total fuel loads were 7 × higher in controls (6015 kg ha−1) than burned plots (831 kg ha−1; P < 0.01). Herbaceous fuels were 5 times greater in burns (P < 0. 01). Shrub fuel was nearly 10 times higher in unburned plots (P < 0.01), and litter under shrubs in controls was 3.75 times greater than in burns (P < 0.01). Potential fire behavior was lower in burned plots than in unburned controls across all environmental scenarios. In the driest scenario, potential rate of spread ranged from 0.4 to 1.5 m min−1 in burns and 2.7 to 5.5 m min−1 in controls (P < 0.01). Maintaining resilience in these ecosystems at multiple spatial and temporal scales may include a consideration of the natural role of fire in good condition Wyoming big sagebrush ecosystems. This study shows that under these conditions, fire can promote good condition mid-successional ecosystems and can act as a fuel break, slowing the spread and decreasing the intensity of a future wildfire.

Ecosystem resilience is evident 17 years after fire in Wyoming big sagebrush ecosystems

AbstractRecent policy has focused on prevention of wildfire in the sagebrush steppe in an effort to protect habitat for the greater sage grouse (Centrocercus urophasianus). Historically, fire return intervals in Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) ecosystems were 50–100 yr or more, but invasive species, climate change, and a legacy of intensive grazing practices have led to degraded rangeland condition, altered fire regimes and fire effects, and declines in sagebrush cover. Little is known about the long‐term impacts of fire in this ecosystem in areas where grazing pressure has been removed, few invasive species exist, and fire return intervals are maintained. In this study, we quantified vegetation composition prior to prescribed burning, 1 year following fire, and 17 years after fire in a native‐dominated Wyoming big sagebrush ecosystem at Hart Mountain National Antelope Refuge, Oregon, United States. Seventeen years following fire, the ecosystem was dominated by native herbaceous vegetation, with 8.3% cover of broad‐leaved forbs and bunchgrasses in the understory, compared to just 3.8% cover of native herbaceous vegetation in unburned controls. Invasive annual grass cover ranged from 0.2% to 8.4% across all treatments and years (P = 0.56). One year following fire, the distance from a randomly located point and the nearest mature sagebrush was 16.6 m, but by 17 years after the fire, that distance had decreased to 2.5 m. Seventeen years after fires, shrub cover was 0.4–4% in burned plots compared to 13–24% in unburned controls. Collectively, these data demonstrate that good condition ungrazed Wyoming big sagebrush plant communities exhibited resilience following fire and maintained a native‐dominated mosaic of shrubs, bunchgrasses, and forbs. Further, unburned control plots were dominated by woody vegetation and exhibited losses in herbaceous understory, possibly indicating that they are outside of their natural fire return interval. Our results illustrate that management of all habitat components, including natural disturbance and a mosaic of successional stages, is important for persistent resilience and that suppression of all fires in the sagebrush steppe may create long‐term losses of heterogeneity in good condition Wyoming big sagebrush ecosystems.

Restoration of riparian areas following the removal of cattle in the northwestern great basin.

We assessed the effects of the elimination of livestock in riparian systems at Hart Mountain National Antelope Refuge in southeastern Oregon, 23 years after the removal of cattle grazing, using 64 photos taken before grazing was removed compared with later retake photos. Two methods were used for this assessment: (1) a qualitative visual method comparing seven cover types and processes and (2) a new quantitative method of inserting digital line transects into photos. Results indicated that channel widths and eroding banks decreased in 64 and 73% of sites, respectively. We found a 90% decrease in the amount of bare soil (P < 0.001) and a 63% decrease in exposed channel (P < 0.001) as well as a significant increase in the cover of grasses/sedges/forbs (15% increase, P = 0.037), rushes (389% increase, P = 0.014), and willow (388% increase, P < 0.001). We also assessed the accuracy of the new method of inserting digital line transects into photo pairs. An overall accuracy of 91% (kappa 83%) suggests that digital line transects can be a useful tool for quantifying vegetation cover from photos. Our results indicate that the removal of cattle can result in dramatic changes in riparian vegetation, even in semi-arid landscapes and without replanting or other active restoration efforts.

Long-term livestock grazing alters aspen age structure in the northwestern Great Basin

We determined the age structure of quaking aspen (Populus tremuloides) over the period 1850–2009 in Hart Mountain National Antelope Refuge riparian areas to evaluate potential influences of (a) livestock herbivory and (b) climate on aspen demography. We found a significant decline in aspen recruitment (p<0.05) in the late 1800s, coincident with the onset of high levels of Euro-American livestock grazing. Although livestock use was regulated following establishment of the refuge in 1936, low levels of aspen recruitment continued. After termination of livestock grazing in 1990, aspen recruitment on the refuge increased (p<0.05) by more than an order of magnitude in comparison to levels occurring during the previous half-century of regulated grazing. Climate variables (i.e., Palmer Drought Severity Index, annual precipitation, and annual temperature) appeared to have little influence on long-term patterns of aspen recruitment. Overall, results are consistent with top–down forcing by livestock herbivory as the major factor associated with a century of reduced aspen recruitment on HMNAR. Where long-term declines in aspen are currently underway on grazed lands in the western US, land managers need to carefully consider the potential effects of livestock and alter, as needed, management of these ungulates to ensure retention of aspen woodlands and their ecosystem services.

Predictive modeling and mapping sage grouse ( Centrocercus urophasianus) nesting habitat using Maximum Entropy and a long-term dataset from Southern Oregon

Predictive modeling and mapping based on the quantitative relationships between a species and the biophysical features (predictor variables) of the ecosystem in which it occurs can provide fundamental information for developing sustainable resource management policies for species and ecosystems. To create management strategies with the goal of sustaining a species such as sage grouse ( Centrocercus urophasianus), whose distribution throughout North America has declined by approximately 50%, land management agencies need to know what attributes of the range they now inhabit will keep populations sustainable and which attributes attract disproportionate levels of use within a home range. The objectives of this study were to 1) quantify the relationships between sage grouse nest-site locations and a set of associated biophysical attributes using Maximum Entropy, 2) find the best subset of predictor variables that explain the data adequately, 3) create quantitative sage grouse distribution maps representing the relative likelihood of nest-site habitat based on those relationships, and 3) evaluate the implications of the results for future management of sage grouse. Nest-site location data from 1995 to 2003 were collected as part of a long-term research program on sage grouse reproductive ecology at Hart Mountain National Antelope Refuge. Two types of models were created: 1) with a set of predictor variables derived from digital elevation models, a field-validated vegetation classification, and UTM coordinates and 2) with the same predictors and UTM coordinates excluded. East UTM emerged as the most important predictor variable in the first type of model followed by the vegetation classification which was the most important predictor in the second type of model. The average training gain from ten modeling runs using all presence records and randomized background points was used to select the best subset of predictors. A predictive map of sage grouse nest-site habitat created from the application of the model to the study area showed strong overlap between model predictions and nest-site locations.

Initial Effects of Prescribed Fire on Morphology, Abundance, and Phenology of Forbs in Big Sagebrush Communities in Southeastern Oregon

Abstract Historic fire return intervals in Artemesia tridentata (big sagebrush) ecosystems have been altered by livestock grazing, fire suppression, and other land management techniques resulting in ecological changes in these areas. Increases in abundance of woody vegetation may be causing declines in native herbaceous understory species. We examined the effects of prescribed fire on the morphology, abundance, and phenology of nine abundant forb (herbaceous dicot) species used selectively by Centrocercus urophasianus (Sage Grouse). In September 1997 prescribed fire was applied to four of eight randomly assigned 400‐ha A.t. wyomingensis (Wyoming big sagebrush) study plots at Hart Mountain National Antelope Refuge, Oregon. Livestock had not grazed experimental plots since 1991. Burning caused morphological changes such as significantly greater numbers of racemes and flowers per raceme in Astragalus malachus (shaggy milkvetch‐Legumoideae) (9 in burn vs. 6 in control; 23 in burn vs. 21 in control, respectively). Also, prescribed burning caused greater numbers of flowers in Phlox gracilis (microsteris‐Polemoniaceae) (57 vs. 13), greater numbers of umbels and umbelletts in Lomatium nevadense (Nevada desert parsley‐Umbellifereae) (4 vs. 2 and 59 vs. 31, respectively), greater numbers of flower heads in Crepis modocensis (Modoc hawksbeard‐Compositae) (32 vs. 21), and greater number of flowers/cm3 in Phlox longifolia (longleaf phlox‐Polemoniaceae) (0.11 vs. 0.06). Crown volume of Crepis modocensis (7,085 vs. 4,179 cm3) and Astragalus malachus (2,854 vs. 1,761 cm3) plants was greater in burned plots than control plots. However, burning resulted in a smaller crown area of Antennaria dimorpha (low pussytoes‐Compositae) (20 vs. 37 cm2). Phenology and time of flowering were also affected by fire. The period of active growth for each species was extended later into the summer in burned plots ( p &lt; 0.01). In addition, Crepis modocensis and Lomatium nevadense flowered 12 to 14 days earlier in burned plots. Fire had no effect on frequency, density, and relative abundance of seven of the nine studied species. Fire reduced the frequency and relative abundance of A. dimorpha and Phlox longifolia and reduced the density of A. dimorpha.

Blood parasites in sage-grouse from Nevada and Oregon.

Peripheral blood smears from 196 adult and yearling female greater sage-grouse (Centrocercus urophasianus) were examined for blood parasites (167 from the breeding and 29 from the brood-rearing season) to determine prevalence of blood parasites, to attempt to correlate infection with chick survival, and to establish base-line values of prevalence in sage-grouse from Nevada and Oregon (USA). Birds were captured and released on two study areas during 1999-2001; Sheldon National Wildlife Refuge (SNWR) in northwestern Nevada, and Hart Mountain National Antelope Refuge (HMNAR) in southeastern Oregon. Birds from a third study area, Beaty's Butte grazing allotment (BB) in southeastern Oregon, were sampled in 2000 and 2001. Overall, 19 birds (10%) were positive for Leucocytozoon lovati (= L. bonasae), 1 (0.5%) for Plasmodium pedioecetii, and 2 (1%) for microfilariae. Although prevalence of L. lovati on HMNAR was 39% during the breeding season in 1999 and 100% during the brood-rearing season in 2000, statistically, prevalence of L. lovati among study areas and years was not different. However, there were statistical differences between capture periods. Overall, 31% of the hens were positive for L. lovati during the brood-rearing season compared to 6% during the breeding season. There was no difference in packed cell volume between infected and non-infected birds and no difference between age-classes. However, mean sage-grouse productivity on HMNAR was higher (1.6 chicks/hen) for non-infected (n = 10) compared to infected hens (0.7 chicks/hen; n = 7), during 1999. Based on these limited observations on HMNAR in 1999, the possible effects that L. lovati may have on young sage-grouse could be detrimental to sage-grouse populations in Nevada and Oregon.

Birth Synchrony and Survival of Pronghorn Fawns

Predation is often the primary mortality factor of neonatal pronghorn (Antilocapra americana). Birth synchrony can affect predation rates of young for some ungulates, but has not been examined in pronghorn. We investigated causes of mortality and the effect of birth synchrony on survival of neonatal pronghorn (n = 104) at Hart Mountain National Antelope Refuge in southcentral Oregon from mid-May to mid-July in 1996 and 1997. Most (84%) of the marked fawns died during the monitoring period. Average age at death was 8.4 days and 83 (95%) of the fawns that died were < 18 days old. Predation, primarily coyote (Canis latrans), accounted for 86% (75/87) of the fawn deaths. Birth date affected survival where neonates born during the peak period of fawn drop lived longer than those born during the non-peak period (P ≤ 0.002). Of 17 surviving fawns, 14 had birth dates during the peak fawning period compared to 3 born during the non peak period (P = 0.024). Survival rates for all fawns born during the peak fawning period (S 60 = 0.23) were greater (P < 0.001) than fawns born during the non-peak period (S 60 = 0.07). Our results indicated that birth synchrony in pronghorn may be an important adaptation through which losses of young to predation can be reduced.

Septicemic pasteurellosis in free-ranging neonatal pronghorn in Oregon.

As part of a study to determine the cause(s) of population decline and low survival of pronghorn (Antilocapra americana) neonates on Hart Mountain National Antelope Refuge (HMNAR), Oregon (USA), 55 of 104 neonates captured during May 1996 and 1997 were necropsied (n = 28, 1996; n = 27, 1997) to determine cause of death. Necropsies were conducted on fawns that died during May, June, or July of each year. The objectives of this study were to report the occurrence and pathology of pasteurellosis in neonates and determine if the isolated strain of Pasteurella multocida was unique. Septicemic pasteurellosis, caused by P. multocida, was diagnosed as the cause of death for two neonates in May and June 1997. Necropsy findings included widely scattered petechial and ecchymotic hemorrhages found over a large portion of the subcutaneous tissue, meninges of the brain, epicardium, skeletal muscle, and serosal surface of the thorasic and abdominal cavities. Histological examination of lung tissues revealed diffuse congestion and edema and moderate to marked multifocal infiltrate of macrophages, neutrophils, and numerous bacteria within many terminal bronchioles and alveoli. Pasteurella multocida serotypes A:3,4, and B:1 were isolated from several tissues including lung, intestinal, thorasic fluid, and heart blood. Each B:1 isolate had DNA restriction endonuclease fingerprint profiles distinct from isolates previously characterized from domestic cattle, swan (Olor spp.), moose (Alces alces), and pronghorn from Montana (USA). This is the first report of pasteurellosis in pronghorn from Oregon and the B:1 isolates appear to be unique in comparison to DNA fingerprint profiles from selected domestic and wild species.

Health evaluation of a pronghorn antelope population in Oregon.

During 1996 and 1997, the U.S. Fish and Wildlife Service conducted a study to determine the cause(s) of population decline and low survival of pronghorn antelope (Antilocapra americana) fawns on Hart Mountain National Antelope Refuge (HMNAR) located in southeastern Oregon (USA). As part of that study, blood, fecal, and tissue samples from 104 neonatal fawns, 40 adult does, and nine adult male pronghorns were collected to conduct a health evaluation of the population. Physiological parameters related to nutrition and/or disease were studied. No abnormalities were found in the complete blood cell counts of adults (n = 40) or fawns (n = 44 to 67). Serum total protein and blood urea nitrogen (BUN) levels were lower compared to other pronghorn populations. Does had mean BUN values significantly lower (P < 0.001) in December 1996 than March 1997. Serum copper (Cu) levels in does (range 0.39 to 0.74 ppm) were considered marginal when compared to domestic animals and other wild ungulates. Fawns had low (0.28 ppm) Cu levels at birth and reached the does' marginal values in about 3 days. Whole blood, serum and liver selenium (Se) levels were considered marginal to low in most segments of the pronghorn population. However, serum levels of vitamin E (range 1.98 to 3.27 microg/ml), as determined from the does captured in March, were apparently sufficient to offset any signs of Se deficiency. No clinical signs of Cu or Se deficiency were observed. Fifty-five of 87 dead fawns were necropsied. Trauma, due to predation by coyotes (Canis latrans), accounted for 62% of the mortality during mid-May to mid-July of each year. Other causes included predation by golden eagles (Aquila chrysaetos) (4%), dystocia (2%), septicemic pasteurellosis (4%), starvation (5%), and unknown (23%). Adult females were tested for serum neutralizing antibodies to Brucella spp. (n = 20, negative), Leptospira interrogans (n = 20, negative), bluetongue virus (n = 20, 35% positive), epizootic hemorrhagic disease virus (n = 20, 30% positive), respiratory syncytial virus (n = 18, negative), parainfluenza virus type 3 (n = 18, 67% positive), infectious bovine rhinotracheitis (n = 18, negative), and bovine viral diarrhea (n = 18, negative). Considering the parameters examined, we found no apparent predisposing factors to mortality including those killed by coyotes, but some nutritional parameters suggest that pronghorns on HMNAR exist on a diet low in protein and Se and marginal in Cu. The effect these factors have on the population is not known.

Sexual Segregation in Rocky Mountain Mule Deer

Two leading explanations for sexual segregation in polygynous ungulates include the reproductive-strategy and the sexual dimorphism-body size hypotheses. We tested predictions of these hypotheses by comparing habitat use, characteristics of feeding sites, diet composition, and diet quality between male and female mule deer (Odocoileus hemionus hemionus) at Hart Mountain National Antelope Refuge (HMNAR) in southeastern Oregon. Females selected mesic and bitterbrush cover types (P 10° more than males or coyotes(P 10°. Females were observed closer to water than males (P 75%). Concentrations of diaminopimelic acid (DAPA), an index of diet quality, were higher in fecal samples of males than females (P < 0.01). Our data supported predictions of the reproductive-strategy hypothesis that sexual segregation occurred as the result of different strategies by males and females to enhance reproductive fitness. Females used areas of low coyote activity, high security benefits, palatable browse resources, and proximity to water, all of which are likely to increase offspring survival. Males used areas that maximized foraging opportunities for preferred diet items. Because males foraged in areas with greater biomass and species richness of forbs and obtained a higher-quality diet than females, we rejected the sexual dimorphism-body size hypothesis that predicts males would segregate to areas of more abundant, lower-quality forage.

Availability of Foods of Sage Grouse Chicks following Prescribed Fire in Sagebrush-Bitterbrush

A study was conducted to determine the influence of prescribed fire on the availability of primary foods of sage grouse (Centrocercus urophasianus Bonaparte) chicks at Hart Mountain National Antelope Refuge, Lake County, Ore. from 1987 to 1989. Responses of certain primary foods and general food categories to fire were evaluated in sagebrush (Artemisia tridentata ssp. vaseyana Beetle)-bitterbrush (Purshia tridentata Pursh.) communities with a randomized block design established in stands where shrub cover exceeded 35%. Within blocks, habitat response was evaluated for 2 growing seasons on 4 pots used as controls, 3 plots burned in November 1987, and 4 plots burned in March 1988. Fall burning increased (P < 0.05) frequency of taxa in the dandelion tribe (Cichorieae). Other primary foods, including microsteris (Microsteris gracilis Hook.), desert-parsley (Lomatium spp. Raf.), and ground-dwelling beetles (Scarabaeidae, Tenebrionidae) were not influenced by burning. Spring and fall burning increased (P < 0.05) total forte cover and diversity, but decreased (P < 0.05) sagebrush cover. Prescribed fire may increase the supply of forbs available to sage grouse in montane sagebrush habitats used for brood-rearing where shrubs dominate stands at the expense of the herbaceous component.

Intraspecific Predation on American Marten

Acknawledgements. The senior author thanks the Rob & Bessie Welder Wildlife Foundation for support making this and other research efforts possible. Both authors extend their thanks for assistance and samples provided by personnel at Hart Mountain National Antelope Refuge and for critical comments provided by B. Coblentz, G. Matson, D. Olson, and an anonymous reviewer. Oregon Agricultural Experiment Station technical paper no. 10,843.