Scientific Publications from the Greater Hart-Sheldon
Decades of scientific study in the Greater Hart-Sheldon support permanently protecting the region’s unique and outstanding natural values.
Below is a selection of peer-reviewed published research from the region.
Greater Hart-Sheldon Literature
Batchelor, J.L., Ripple, W.J., Wilson, T.M. and Painter, L.E., 2015. Restoration of riparian areas following the removal of cattle in the Northwestern Great Basin. Environmental Management, 55(4), pp.930-942.
Abstract: 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.
Beschta, R.L., Kauffman, J.B., Dobkin, D.S. and Ellsworth, L.M., 2014. Long-term livestock grazing alters aspen age structure in the northwestern Great Basin. Forest ecology and management, 329, pp.30-36.
Abstract: 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.
Collins, G. H. 2016. Seasonal distribution and routes of pronghorn in the northern Great Basin. Western North American Naturalist 76:101–112.
Abstract: Pronghorn (Antilocapra americana) exhibit complex spatial and temporal variation in seasonal movements and range use across their distribution. However, knowledge of seasonal movements, routes, and distribution of pronghorn within the sagebrush-steppe of the northern Great Basin is lacking. From October 2011 to October 2013, I monitored movements of adult female pronghorn across an area of over 1.5 million hectares along the northwestern Nevada and southeastern Oregon border using GPS/VHF-equipped collars. I used 68,834 GPS locations from 32 female pronghorn to determine migration timing, seasonal distributions, individual fidelity to winter and summer ranges, and population-level routes used during the migration period. Collared pronghorn were conditionally migratory, with 65% migrating an average of 30.0 km the first year and 100% migrating an average of 39.1 km the second; one individual migrated over 160 km between summer and winter ranges. Seasonal ranges averaged 143.3 km2 during the summer, and from 252.9 to 459.9 km2 during the winter (2010/2011 and 2011/2012, respectively). Individual pronghorn demonstrated wide variation in directional movement between summer and winter ranges, and there was high overlap of common areas across seasons and time periods. Pronghorn showed stronger fidelity to summer ranges than to winter ranges, and occupied higher elevations during the summer months, descending to lower elevations during the winter. Deeper snow and colder temperatures in 2012/2013 compared to 2011/2012 corresponded to longer average migration distances, fewer exploratory movements, larger winter ranges, lower elevational use, and a shift in winter range location. Habitat conversion, degradation, and fragmentation have accumulated across the sagebrush-steppe biome and are negatively affecting the long-term persistence of dependent wildlife. Applying knowledge of important seasonal use areas and routes used during migration in future conservation planning can mitigate impacts to pronghorn habitat and provide for long-term conservation.
Collins, G.H. and Bauman, B.T., 2012. Distribution of low-elevation American pika populations in the northern Great Basin. Journal of Fish and Wildlife Management, 3(2), pp.311-318.
Abstract: The recent discovery that a portion of the historically described populations of American pikas Ochotona princeps in the Great Basin of North America appear to be extinct added emphasis to earlier warnings that these populations may be highly vulnerable, in particular those occurring at low elevations (,2,500 m). Pikas in the Great Basin have received increased scientific interest; however, there is still little known about the distribution or number of populations throughout their range. Here we report on the discovery of several previously undescribed low-elevation pika populations in Southeast Oregon and Northwest Nevada. The average elevation of sites currently occupied by pikas was 1,993 m (range = 1,648–2,357 m). This and other recent discoveries suggest that pikas may be more common at low elevations in portions of the northern Great Basin than previously suspected (i.e., .2,500 m).
Davies, K.W. and Bates, J.D., 2020. Re-introducing fire in sagebrush steppe experiencing decreased fire frequency: does burning promote spatial and temporal heterogeneity?. International Journal of Wildland Fire, 29(8), pp.686-695.
Abstract: Fire frequency has decreased in many shrub-steppe communities. Re-introducing fire may be needed to increase spatial and temporal variability in vegetation, but is often hindered by concerns of undesired vegetation shifts. These concerns arise, in part, because long-term effects of fire re-introduction in these communities after prolonged fire exclusion and other departures from historical conditions are unknown. To better understand the effects of reintroducing fire, we evaluated plant community response to re-introducing fire for 12 years post fire in six mountain big sagebrush communities. Herbaceous biomass production was 1.7-fold greater in burned compared with unburned areas at the conclusion of the study. Exotic annual grasses appeared to be problematic in the first 8 years post fire, but became inconsequential (~1% cover) by the end of the study. Re-introducing fire promoted other shrubs (excluding sagebrush) that were probably inhibited by competition from sagebrush. Sagebrush cover and density remained low in burned areas for the duration of the study, because of limited recruitment in the years immediately post fire and competition from herbaceous vegetation. Re-introducing fire appears to increase temporal and spatial heterogeneity in shrub-steppe communities experiencing prolonged fire exclusion and, therefore, may be needed to maintain a diversity of plant communities.
Davis, D.M. and Crawford, J.A., 2015. Case study: Short‐term response of greater sage‐grouse habitats to wildfire in mountain big sagebrush communities. Wildlife Society Bulletin, 39(1), pp.129-137.
Abstract: Our case study evaluated the short-term (<11 yr) implications of wildfire on greater sage-grouse (Centrocercus urophasianus) breeding-season habitat (i.e., nesting and brood-rearing) and ground-dwelling arthropod abundance on Sheldon National Wildlife Refuge in northwestern Nevada, USA. Two different-aged wildfire sites were sampled in mountain big sagebrush (Artemisia tridentata vaseyana) cover types in 1998 and 1999. Plant communities in burned and associated unburned areas did not differ appreciably in species composition and wildfire did not negatively impact arthropod abundance. Wildfires did not increase the frequency of exotic plant species, such as cheatgrass (Bromus tectorum), nor did wildfire have a detrimental effect on native perennial bunchgrasses. Wildfires were effective at changing the mountain big sagebrush community structure from shrub-dominated to one dominated by native grasses and forbs 2–3 yr post-burn. However, the absence of shrub cover following 2–3 yr of post-fire recovery indicates our overall estimates of vegetation structure were not consistent with published guideline requirements for managing sage-grouse breeding-season habitat. Although burning had little stimulatory effect on total forb cover 10–11 yr post-burn, the vegetation and structural components needed to maintain suitable sage-grouse nesting and brood-rearing habitats were present in the burned site. The short-term habitat response to wildfire suggests prescribed fire can be a useful tool to achieve management objectives by manipulating vegetation structure and composition of shrub-dominated landscapes. However, land managers should be cautious using prescribed fire as a management tool in big sagebrush ecosystems if the goal is to improve sage-grouse habitats.
DeLong, A.K., Crawford, J.A. and DeLong Jr, D.C., 1995. Relationships between vegetational structure and predation of artificial sage grouse nests. The Journal of wildlife management, pp.88-92.
Abstract: Because of high nest predation and long-term declines in sage grouse (Centrocercus urophasianus) productivity in Oregon, we assessed the effects of vegetational cover and height on predation of artificial sage grouse nests (n = 330). Artificial nest fate was positively associated with tall grass cover and medium height shrub cover collectively (P = 0.01). No other vegetation, predator, temporal, or spatial variables explained any additional variation in the probability of predation. This study supports the hypothesis that greater amounts of tall grass and medium-height shrub cover at nest sites lower risk of nest predation for sage grouse. Management practices that increase cover and height of native grasses in sagebrush communities with medium-height shrubs are recommended to enhance sage grouse productivity.
Dobkin, D.S., Rich, A.C., Pretare, J.A. and Pyle, W.H., 1995. Nest-site relationships among cavity-nesting birds of riparian and snowpocket aspen woodlands in the northwestern Great Basin. The Condor, 97(3), pp.694-707.
Abstract: We examined nest-site and nest-cavity characteristics for six species of cavity nesting birds in montane riparian and snowpocket aspen (Populus tremuloides) woodlands in the northwestern Great Basin. Live trees and snags with DBH >24 cm were favored as nest sites by all species. Red-naped Sapsuckers (Sphyrapicus nuchalis) and Northern Flickers (Colaptes auratus) provided different sizes of nest cavities for a suite of nonexcavator species. Flickers preferentially nested in snags; sapsuckers nested primarily in live trees, but used live trees and snags in proportion to their availabilities. Relative abundances of excavators and nonexcavators were associated positively with numbers of cavities. Nest-site variables overlapped extensively among species; Tree Swallows (Tachycineta bicolor) relied heavily on sapsuckers for provision of nest cavities, European Starlings (Sturnus vulgaris) and Mountain Bluebirds (Sialia currucoides) primarily used flicker-excavated cavities, and House Wrens (Troglodytes aedon) used nest cavities across the broadest range of nest-site characteristics. Compass orientation of nest-cavity entrances was strongly bimodal, with most facing east or southwest. Cavity entrances of species that foraged largely outside of riparian woodlands were oriented toward woodland edge, in contrast to nest cavities used by species that foraged largely within riparian woodlands. Snowpocket woodlands were much more extensive than riparian aspen, but birds strongly preferred riparian aspen stands as nesting habitats, presumably due to the scarcity of large aspen in snowpockets. Nest cavities appear to be a limiting resource with high potential for interspecific nest-site competition in these woodlands. Decades of livestock overuse and fire suppression have greatly diminished the availability of large aspen in riparian habitats throughout the region.
Dobkin, D.S., Rich, A.C. and Pyle, W.H., 1998. Habitat and avifaunal recovery from livestock grazing in a riparian meadow system of the northwestern Great Basin. Conservation Biology, 12(1), pp.209-221.
Abstract: Riparian habitats are centers of biological diversity in arid and semiarid portions of western North America, but despite widespread loss and degradation of these habitats there is little quantitative information concerning restoration of native riparian biota. We examined the recovery of a riparian meadow system in the context of long-term versus short-term release from livestock grazing. We compared the structure and dynamics of plant and avian communities on 1.5-ha plots inside a long-term (>30 years) livestock exclosure (“exclosure plots”), with adjacent plots outside the exclosure (“open plots”) for 4 years following removal of livestock from open plots. Throughout the study, sedge cover, forb cover, and foliage height diversity of herbs were greater on exclosure plots; bare ground, litter cover, shrub cover, and shrub foliage height diversity were greater on open plots. Forb, rush, and cryptogamic cover increased on open plots but not on exclosure plots. Grass cover increased, whereas litter and bare ground decreased on all plots in conjunction with increased availability of moisture. Sedge cover did not change. Avian species richness and relative abundances were greater on exclosure plots; species composition differed markedly between exclosure and open plots ( Jaccard Coefficient =0.23–0.46), with exclosure plots dominated by wetland and riparian birds and open plots dominated by upland species. The appearance of key species of wet-meadow birds on open plots in the third and fourth years following livestock removal signaled the beginning of restoration of the riparian avifauna. We interpret the recovery of riparian vegetation and avifaunal composition inside the exclosure as a consequence of livestock removal, which led to a rise in the water table and an expansion of the hyporheic zone laterally from the stream channel. The lack of change in sedge and shrub cover on open plots suggests that restoration to a sedge-dominated meadow will not happen quickly.
Drut, M.S., Crawford, J.A. and Gregg, M.A., 1994. Brood habitat use by sage grouse in Oregon. The Great Basin Naturalist, pp.170-176.
Abstract: Habitat use by Sage Grouse (Centrocerc1l.s uropharianus) hens with broods was examined at Jackass Creek and Hart Mountain, Oregon, from 1989 through 1991. Sage Grouse hens initially selected low sagebrush (Artemirio spp.) cover types during early brood-rearing, big sagebrush cover types later in the brood-rearing period, and ultimately concentrated use in and near lakebeds and meadows. Areas used by Sage Grouse broods typically had greater forb frequency than did random sites. Hens at Jackass Creek selected sites with forb cover similar to that generally available to broods at Hart Mountain, but home ranges were larger at Jackass Creek because of lower availability of suitable brood-rearing habitat. Differences in habitat use by broods on the two areas were reflected in dietary differences; at Hart Mountain, chicks primarily ate forbs and insects, whereas at Jackass Creek most of the diet was sagebrush. Larger home ranges, differences in diets, and differences in availability of forb-rich habitats possibly were related to differences in abundance and productivity between areas.
Dunbar, M.R., Gregg, M.A., Crawford, J.A., Giordano, M.R. and Tornquist, S.J., 2005. Normal hematologic and biochemical values for prelaying greater sage grouse (Centrocercus urophasianus) and their influence on chick survival. Journal of Zoo and Wildlife Medicine, 36(3), pp.422-429.
Abstract: Declines in greater sage grouse (Centrocercus urophasianus) productivity and population numbers throughout their range demand a better understanding of how nutrition influences sage grouse populations. During March and April 1999–2001, blood samples were collected from 158 female (73 adult, 85 yearling), free-ranging, prelaying, greater sage grouse from an area in northwestern Nevada, USA, and southeastern Oregon, USA. These blood samples were evaluated to establish normal blood values for sage grouse and ascertain if certain blood parameters, as indices of nutrition, are useful for predicting if sage grouse hens would raise at least one chick to 1 August. Results of logistic regression indicated that three of six blood parameters analyzed—glucose, total plasma protein, and calcium : phosphorus ratio—affected the probability of a female sage grouse raising at least one chick to late summer. Ranking of the standardized estimates revealed that glucose and total plasma protein had the greatest impact on the likelihood of a female successfully raising chicks. Odds ratios indicated that a 1-unit increase in glucose (1 mg/dl) and plasma protein (0.1 g/dl) would result in a 4% and 113% positive increase, respectively, in the predicted odds of at least one chick surviving until 1 August. Odds ratios for calcium : phosphorus ratio revealed a 70% decline in the predicted odds of at least one chick surviving until 1 August if the level of this parameter increased one unit (e.g., 3:1 to 4:1). Based on these analyses, values of some blood parameters used as indices of nutrition, especially glucose, total plasma protein, and calcium : phosphorus ratio, can be successfully used to predict reproductive success of sage grouse. These parameters are not only indicative of the nutritional status of prelaying hens but may be associated with nutritional quality of the habitat and therefore have important management significance.
Earnst, S.L., Ballard, J.A. and Dobkin, D.S., 2005. Riparian songbird abundance a decade after cattle removal on Hart Mountain and Sheldon National Wildlife Refuges. In In: Ralph, C. John; Rich, Terrell D., editors 2005. Bird Conservation Implementation and Integration in the Americas: Proceedings of the Third International Partners in Flight Conference. 2002 March 20-24; Asilomar, California, Volume 1 Gen. Tech. Rep. PSW-GTR-191. Albany, CA: US Dept. of Agriculture, Forest Service, Pacific Southwest Research Station: p. 550-558 (Vol. 191).
Abstract: Cattle were removed from the high desert riparian habitats of Hart Mountain and Sheldon National Wildlife Refuges in 1990. This study compares songbird abundance in 2000-2001 to that in 1991-1993 on 69 permanent plots. Of the 51 species for which detections were sufficient to calculate changes in abundance, 71 percent (36/51) exhibited a positive trend and 76 percent (16/21) of species exhibiting a significant change (either positive or negative) increased. The average increase among the 51 species was equivalent to 3.0 detections/km2. Increasing species included species of concern in the Columbia Plateau: Yellow Warbler (Dendroica petechia), White-crowned Sparrow (Zonotrichia leucophrys), Song Sparrow (Melospiza melodia), Dusky Flycatcher (Empidonax oberholseri), Warbling Vireo (Vireo gilvus), Mourning Dove (Zenaida macroura), MacGillivray’s Warbler (Oporornis tolmiei), and Orange-crowned Warbler (Vermivora celata). Aspen and willow associates, but not meadow associates, exhibited a significant increase in detections/km2. Detections of ground/low cup and high cup nesting species, but not cavity nesting species, increased significantly. Ground/understory foraging species, aerial, and overstory foraging species increased significantly in detections/km2, but bark gleaning species did not. For the 16 significantly increasing species in this study, patterns of change on Breeding Bird Survey routes during 1980-1999 suggest that the changes documented here are not merely a reflection of regional patterns.
Earnst, S.L., Dobkin, D.S. and Ballard, J.A., 2012. Changes in avian and plant communities of aspen woodlands over 12 years after livestock removal in the northwestern Great Basin. Conservation Biology, 26(5), pp.862-872.
Abstract: Riparian and quaking aspen (Populus tremuloides) woodlands are centers of avian abundance and diversity in the western United States, but they have been affected adversely by land use practices, particularly livestock grazing. In 1990, cattle were removed from a 112,500-ha national wildlife refuge in southeastern Oregon. Thereafter, we monitored changes in vegetation and bird abundance in years 1–3 (phase 1) and 10–12 (phase 2) in 17 riparian and 9 snow-pocket aspen plots. On each 1.5-ha plot, we sampled vegetation in 6 transects. Three times during each breeding season, observers recorded all birds 50 m to each side of the plot’s 150-m centerline for 25 minutes. We analyzed data with multivariate analysis of variance and paired t tests with p values adjusted for multiple comparisons. In both periods, riparian and snow-pocket aspen produced extensive regeneration of new shoots ( ¯x = 2646 stems/ha and 7079 stems/ha, respectively). By phase 2, a 64% increase in medium-diameter trees in riparian stands indicated successful recruitment into the overstory, but this pattern was not seen in snow-pocket stands, where the density of trees was over 2 times greater. By phase 2 in riparian and snow-pocket stands, native forb cover had increased by 68% and 57%, respectively, mesic shrub cover had increased by 29% and 58%, and sagebrush cover had decreased by 24% and 31%. Total avian abundance increased by 33% and 39% in riparian and snow-pocket aspen, respectively, ground or understory nesters increased by 133% and 67% and overstory nesters increased by 34% and 33%. Similarly, ground or understory foragers increased by 25% and 32%, aerial foragers by 55% and 57%, and overstory foragers by 66% and 43%. We interpreted the substantial regeneration of aspen shoots, increased densities of riparian forbs and shrubs, and increased avian abundances as a multitrophic-level response to the total removal of livestock and as substantial movement toward recovery of biological integrity.
Ellsworth, L.M., Wrobleski, D.W., Kauffman, J.B. and Reis, S.A., 2016. Ecosystem resilience is evident 17 years after fire in Wyoming big sagebrush ecosystems. Ecosphere, 7(12), p.e01618.
Abstract: Recent 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.
Gregg, M.A., Barnett, J.K. and Crawford, J.A., 2008. Temporal variation in diet and nutrition of preincubating greater sage-grouse. Rangeland Ecology & Management, 61(5), pp.535-542.
Abstract: Greater sage-grouse (Centrocercus urophasianus) habitat management involves vegetation manipulations to increase or decrease specific habitat components. For sage-grouse habitat management to be most effective, an understanding of the functional response of sage-grouse to changes in resource availability is critical. We investigated temporal variation in diet composition and nutrient content (crude protein, calcium, and phosphorus) of foods consumed by preincubating female sage grouse relative to food supply and age of hen. We collected 86 preincubating female greater sage-grouse at foraging areas during early (18–31 March) and late (1–12 April) preincubation periods during 2002–2003. Females consumed 22 food types including low sagebrush (Artemisia arbuscula Nutt.), big sagebrush (Artemisia tridentata Nutt.), 15 forb species, 2 insect taxa, sagebrush galls, moss, and a trace amount of unidentified grasses. Low sagebrush was the most common food item, but forbs were found in 89% of the crops and composed 30.1% aggregate dry mass (ADM) of the diet. ADM and species composition of female diets were highly variable between collection periods and years, and coincided with temporal variation in forb availability. Adult females consumed more forbs and less low sagebrush compared to yearling females. Because of higher levels of crude protein, calcium, and phosphorus, forbs were important diet components in comparison with low sagebrush, which had the lowest nutrient content of all foods consumed. Our results indicate that increased forb abundance in areas used by female sage-grouse prior to nesting would increase their forb consumption and nutritional status for reproduction. We recommend that managers should emphasize delineation of habitats used by preincubating sage-grouse and evaluate the need for enhancing forb abundance and diversity.
Gregg, M.A., Crawford, J.A., Drut, M.S. and DeLong, A.K., 1994. Vegetational cover and predation of sage grouse nests in Oregon. The Journal of Wildlife Management, pp.162-166.
Abstract: Because of long-term declines in sage grouse (Centrocercus urophasianus) abundance and productivity in Oregon, we investigated the relationship between vegetational cover and nesting by sage grouse in 2 study areas. Medium height (40-80 cm) shrub cover was greater (P < 0.001) at nonpredated (f = 41%, n = 18) and predated (a = 29%, n = 106) nests than in areas immediately surrounding nests (f = 15 and 10%, n = 18 and 106, nonpredated and predated, respectively) or random locations (f = 8%, n = 499). Tall (>18cm), residual grass cover was greater (P < 0.001) at nonpredated nests (f = 18%)than in areas surrounding nonpredated nests (a = 6%)or random locations (a = 3%).There was no difference (P > 0.05) in grass cover among predated nests, nest areas, and random sites. However, nonpredated nests had greater (P < 0.001) cover of tall, residual grasses (f = 18%)and medium height shrubs (a = 41%)than predated nests (f = 5 and 29% for grasses and shrubs, respectively). Removal of tall grass cover and medium height shrub cover may negatively influence sage grouse productivity.
Gregg, M.A. and Crawford, J.A., 2009. Survival of greater sage‐grouse chicks and broods in the northern Great Basin. The Journal of Wildlife Management, 73(6), pp.904-913.
Abstract: Reduced annual recruitment because of poor habitat quality has been implicated as one of the causative factors in the range‐wide decline of sage‐grouse (Centrocercus urophasianus) populations since the 1950s. Because chick and brood survival are directly linked to annual recruitment and may be the primary factors that limit sage‐grouse population growth, we estimated 28‐day survival rates of radiomarked chicks and broods from 2000 to 2003. We examined relationships between survival and several habitat variables measured at brood sites, including food availability (insects and forbs); horizontal cover of sagebrush, grasses, and forbs; and vertical cover of sagebrush and grass. We monitored 506 radiomarked chicks from 94 broods; chick survival was 0.392 (SE = 0.024). We found evidence that both food and cover variables were positively associated with chick survival, including Lepidoptera availability, slender phlox (Phlox gracilis) frequency, total forb cover, and grass cover. The effect of total grass cover on chick survival was dependent on the proportion of short grass. The hazard of an individual chick’s death decreased 8.6% (95% CI = −1.0 to 18.3) for each percentage point increase in total grass cover when the proportion of short grass was >70%. Survival of 83 radiomarked broods was 0.673 (SE = 0.055). Lepidoptera availability and slender phlox frequency were the only habitat variables related to brood survival. Risk of total brood loss decreased by 11.8% (95% CI = 1.2–22.5) for each additional Lepidoptera individual and 2.7% (95% CI = −0.4 to 5.8) for each percentage point increase in the frequency of slender phlox found at brood sites. Model selection results revealed that temporal differences in brood survival were associated with variation in the availability of Lepidoptera and slender phlox. Years with high brood survival corresponded with years of high Lepidoptera availability and high slender phlox frequency. These foods likely provided high‐quality nutrition for chicks during early growth and development and enhanced survival. Habitat management that promotes Lepidoptera and slender phlox abundance during May and June (i.e., early brood rearing) should have a positive effect on chick and brood survival in the short term and potentially increase annual recruitment.
Gregg, M.A., Dunbar, M.R., Crawford, J.A. and Pope, M.D., 2006. Total plasma protein and renesting by greater sage‐grouse. The Journal of wildlife management, 70(2), pp.472-478.
Abstract: Greater sage-grouse (Centrocercus urophasianus) population declines have been attributed to reduced productivity. Although renesting by sage-grouse may contribute significantly to annual productivity during some years, little information is available on this aspect of sage-grouse reproductive ecology. We investigated the relationship between total plasma protein, age of hen, time of first nest initiation, and time of first nest loss on occurrence of renesting. We captured, assigned age, extracted blood, and radiomarked prelaying, female sage-grouse on 4 study areas during 1999–2004. We monitored radiomarked females from mid-April through June to identify period of nest initiation (early, mid, or late), nest loss (early or late), and renesting activity. We only considered hens that were available to renest (n ¼ 143) for analysis, and we censored those that nested successfully or died during their first nest attempt. Depredation and abandonment accounted for 85% (122/143) and 15% (21/143) of the unsuccessful first nests, respectively. The proportion of hens renesting was 34% (48/143) across all study areas and years. Akaike’s Information Criterion model selection indicated that occurrence of renesting varied by age, nest initiation period, nest loss period, and total plasma protein. The best model had low predictive power for any given hen (r 2 ¼ 0.296), but validation of the best model indicated that our predictor variables were important for distinguishing renesting status and likely explained substantial temporal and spatial variation in renesting rates. A greater proportion of adults than yearlings renested, and hens that nested early in the nesting season and lost nests early during incubation were the most likely to renest. Hens that renested had greater total plasma protein levels than non-renesting hens independent of age, nest initiation period, and nest loss period. Because sage-grouse depend on exogenous sources of protein for reproduction, land management practices that promote high-quality, prelaying hen habitat could increase dietary protein intake and sage-grouse renesting rates.
Larkins, A., Harju, S. and Whittaker, D.G., 2018. Pronghorn migration and survival: A statistical analysis of a southeastern Oregon population. In Proceedings of the Biennial Western States and Provinces Pronghorn Workshop (Vol. 28, pp. 19-28).
Abstract: In January 2015, the Oregon Department of Fish and Wildlife (ODFW) initiated a study on seasonal movements, migratory behavior, and survival of pronghorn (Antilocapra americana) in southeastern Oregon. Fifty female pronghorn were captured on winter range, fitted with Global Positioning System (GPS) collars, and released. Radiocollars recorded GPS locations every 13 hrs and transmitted locations to a central storage server where ODFW personnel downloaded data for analysis. ODFW monitored the location data and mortality signals to identify pronghorn mortalities between January 2015 and July 2017. Objectives of this study were to delineate seasonal range boundaries, identify migration corridors, quantify interchange between Sheldon-Hart National Antelope Refuge properties and surrounding Wildlife Management Units (WMU), quantify interstate movements with Nevada, estimate the percentage of the wintering population remaining in the Beatys Butte WMU (outside of Hart Mountain National Antelope Refuge) through summer and fall that are available to hunters, and to generate annual survival estimates for adult does. We found pronghorn were facultative migrators with variable timing, routes, and distances for migrations. Further, pronghorn used areas on Hart Mountain National Antelope Refuge and areas in Nevada disproportionately on a seasonal basis. Differences in seasonal distributions indicate that boundaries for existing hunting seasons in this area of Oregon need to be expanded to all animals in the population and that annual inventories would be more informative if conducted during summer. Further, additional management coordination across administrative boundaries (state and federal) is necessary to better manage this population.
Reis, S.A., Ellsworth, L.M., Kauffman, J.B. and Wrobleski, D.W., 2019. Long-term effects of fire on vegetation structure and predicted fire behavior in Wyoming big sagebrush ecosystems. Ecosystems, 22(2), pp.257-265.
Abstract: 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 9 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.
Reisner, M.D., Grace, J.B., Pyke, D.A. and Doescher, P.S., 2013. Conditions favouring Bromus tectorum dominance of endangered sagebrush steppe ecosystems. Journal of Applied Ecology, 50(4), pp.1039-1049.
- Ecosystem invasibility is determined by combinations of environmental variables, invader attributes, disturbance regimes, competitive abilities of resident species and evolutionary history between residents and disturbance regimes. Understanding the relative importance of each factor is critical to limiting future invasions and restoring ecosystems.
- We investigated factors potentially controlling Bromus tectorum invasions into Artemisia tridentata ssp. wyomingensis communities across 75 sites in the Great Basin. We measured soil texture, cattle grazing intensity, gaps among perennial plants and plant cover including B. tectorum, biological soil crusts (BSCs) and bare soil. Using a priori knowledge, we developed a multivariate hypothesis of the susceptibility of Artemisia ecosystems to B. tectorum invasion and used the model to assess the relative importance of the factors driving the magnitude of such invasions.
- Model results imply that bunchgrass community structure, abundance and composition, along with BSC cover, play important roles in controlling B. tectorum dominance. Evidence suggests abundant bunchgrasses limit invasions by limiting the size and connectivity of gaps between vegetation, and BSCs appear to limit invasions within gaps. Results also suggest that cattle grazing reduces invasion resistance by decreasing bunchgrass abundance, shifting bunchgrass composition, and thereby increasing connectivity of gaps between perennial plants while trampling further reduces resistance by reducing BSC.
- Synthesis and applications. Grazing exacerbates Bromus tectorum dominance in one of North America’s most endangered ecosystems by adversely impacting key mechanisms mediating resistance to invasion. If the goal is to conserve and restore resistance of these systems, managers should consider maintaining or restoring: (i) high bunchgrass cover and structure characterized by spatially dispersed bunchgrasses and small gaps between them; (ii) a diverse assemblage of bunchgrass species to maximize competitive interactions with B. tectorum in time and space; and (iii) biological soil crusts to limit B. tectorum establishment. Passive restoration by reducing cumulative cattle grazing may be one of the most effective means of achieving these three goals.
Whittaker, D.G., Ostermann, S.D. and Boyce, W.M., 2004. Genetic variability of reintroduced California bighorn sheep in Oregon. The Journal of wildlife management, 68(4), pp.850-859.
Abstract: Of the approximately 2,500 California bighorn sheep (Ovis canadensis californiana) in Oregon, USA, the majority descend from a single transplant of 20 animals from British Columbia, Canada, in 1954. Recently, several populations have experienced poor recruitment, raising concerns that populations may be experiencing inbreeding depression resulting from a genetic bottleneck. We sampled 117 animals from 5 populations in Oregon and 1 population in Nevada to determine genetic variability within and among populations. We found that Oregon populations had fewer mean alleles per locus (2.2-2.4), lower heterozygosity (0.28-0.36), and higher inbreeding potential than animals from Nevada (3.8 alleles/locus, H = 0.53). These results now provide the baseline for rigorous ongoing evaluation of changes to allelic variability, inbreeding potential, variation among populations, and their effects on population demographics for Oregon’s California bighorn sheep program. We suggest that evaluation of genetic variability in other source and recipient populations should be used to further understand how and when genetic management can be used for bighorn sheep conservation and management.
Yost, A.C., Petersen, S.L., Gregg, M. and Miller, R., 2008. Predictive modeling and mapping sage grouse (Centrocercus urophasianus) nesting habitat using Maximum Entropy and a long-term dataset from Southern Oregon. Ecological Informatics, 3(6), pp.375-386.
Abstract: 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.