Ecology and Management of

Transcription

1 Ecology and Management of Sage-Grouse and Sage-Grouse Habitat An Issue Paper Created By the Society for Range Management Current and Potential Pre-settlement Sage Grouse Distribution. From: Scroeder, Michael A., Cameron L. Aldridge, Anthony D. Apa, Joseph R. Bohne, Clait E. Braun, S. Dwight Bunnell, John W. Connelly, Pat A. Deibert, Scott C. Gardner, Mark A. Hilliard, Gerald D. Kobriger, Susan M. McAdam, Clinton W. McCarthy, John J. McCarthy, Dean L. Mitchell, Eric V. Rickerson, and San J. Stiver Distribution of sage grouse in North America. The Condor 106: The sage-grouse is a large, ground-feeding bird that inhabits vast portions of sagebrush rangeland in North America. Two species of sagegrouse have been identified. One species, the greater sage-grouse, historically inhabited much of the western United States and southern portions of British Columbia, Alberta, and Saskatchewan, whereas the Gunnison sage-grouse occupied parts of Colorado, and Utah, and possibly Arizona, and New Mexico (map). There have also been some historic references to sage-grouse in Kansas and Oklahoma. Although the presence of sage-grouse in those states cannot be confirmed, if sagegrouse were ever present in those states they probably would have been Gunnison sage-grouse. Significant ecological changes in sage-grouse habitat and significant reductions in sage-grouse populations have occurred since Euro-American exploration and settlement of the West. Much of the decline in sage-grouse populations can be attributed to direct

2 Female greater sage-grouse sunning on a rock. Photo courtesy of K. Goldie. conversion of native sagebrush rangeland to other uses. An estimated 11.1 million acres of sagebrush rangeland have been converted to cities and towns, communication corridors, non-native pasturelands, or cropland. This direct removal of former sage-grouse habitat largely explains the severe decreases or elimination of sagegrouse from states where very little sagebrush occurred historically and conditions were suitable for more intensive agriculture, such as Nebraska, and North Dakota, and assuming sage-grouse once existed there, Oklahoma and Kansas. Habitat Relationships Although many factors could potentially influence productivity, habitat management is one of the few areas where research has shown that reproductive parameters can be altered. Sage-grouse have specific habitat needs at various stages throughout the year. Some of the important seasonal habitats that sage-grouse use during the year include: Winter Habitat During winter, sage-grouse typically occupy sites with medium to tall sagebrush plants on south and west facing slopes, although areas with shorter sagebrush plants may also be used (particularly on windswept ridges). Severe winter conditions have little effect on sage-grouse populations unless snow completely covers sagebrush, and winter habitat does not usually limit sage-grouse populations. Lekking Habitat Leks, or strutting grounds, are sites where sage-grouse engage in courtship displays and mating in early spring. Leks are typically located on open areas such as knolls or ridges with sparse vegetation that contain few shrubs or other tall vegetation. Sage-grouse leks are usually used year after year and are often located near nesting habitat. Although efforts are made to protect existing lek sites, to avoid any unnecessary disruption to breeding activities, there is no evidence that the availability of potential lek habitat limits sage-grouse populations. Pre-Laying Habitat Greater sage-grouse chick (<3 days old). Forbs and insects are critical in the diet of young sage-grouse. Photo courtesy of US Fish and Wildlife Service. 2 The pre-laying period is the 5-week period prior to nesting when sage-grouse occupy shorter-stature sagebrush communities. During this time, 50-80% of a hen s diet is sagebrush with the remainder being forbs,

3 but the nutrient contribution of forbs during this period overshadows that of sagebrush and may greatly affect reproductive success. Nesting Habitat Sage-grouse nests are generally located within 2 miles of a lek, but in some areas hens may nest much farther from leks. Nests are typically located under sagebrush plants, but other shrubs such as bitterbrush and rabbitbrush may also be used. The most common reason Mountain big sagebrush community used for nesting and for nest failure is predation. Vegetative cover helps hide brood rearing by greater sage-grouse at Hart Mountain nests and makes them less susceptible to predators. National Antelope Refuge, Lake County, Oregon. Photo courtesy of K. Goldie. Because the reproductive success of sage-grouse is often low, the quality and quantity of nesting habitat are likely significant factors affecting sage-grouse populations. Brood-Rearing Habitat Hens with broods (i.e., juvenile birds) are typically found where green forbs are abundant. Forbs and insects comprise the bulk of sage-grouse chicks diets during the first 12 weeks and increased use of riparian habitat during this time is dependent on desiccation of forbs in sagebrush uplands. Availability of forbs and invertebrates directly affects survival of sage-grouse chicks, particularly during drought years. Broodless Hen and Male Habitat Because sage-grouse nesting and brood-rearing success can be very low in some years, a large portion of the summer female populations may be composed of broodless hens, and survival of these hens may be important to long-term population stability. Habitat use by broodless hens is similar to that of hens with broods, but broodless hens move to riparian areas earlier in summer. Male sage-grouse follow a similar pattern but remain in flocks separate from the females. Sage-Grouse Population Ecology Sage-grouse populations usually require several years to respond to changes in habitat management practices. One reason is that the semi-arid climate of sagebrush rangeland limits how quickly and dramatically plants can respond to changes in management practices. Several years, even decades, may be required. Also, sage-grouse have naturally low rates of population growth. Many females (adults and yearlings) do not nest each year, nesting success is low and productivity is further limited by low juvenile survival rates between hatch and the following breeding season. In rare years, however, sage-grouse productivity can be high, and these Mixed mountain big and low sagebrush communities used for nesting and brood rearing by greater sage-grouse at Hart Mountain National Antelope Refuge, Lake County, Oregon. Photo courtesy of K. Goldie. 3

4 infrequent boom years may produce multi-year fluctuations in abundance that make it very difficult to evaluate long-term population responses to habitat changes. Habitat Management Practices Sage-grouse habitat management must consider year-round habitat needs because a deficiency in any one habitat requirement could reduce the productivity and abundance of sage-grouse in an area. Research is needed to refine current knowledge of the optimal combinations of key components within seasonal habitats. Understanding the relationship between habitat variables and juvenile survival is vital to understanding longterm fluctuations of sage-grouse populations. Furthermore, a strong need exists to develop a consistent monitoring approach that focuses on the vegetation elements most important to sage-grouse. Sage-grouse populations can be enhanced or harmed by habitat management practices. Some of the more influential practices include sagebrush control (via prescribed burning, prescribed livestock grazing 1, herbicides, or mechanical treatments), and livestock grazing. Only a few research studies have examined the effects of these management practices on sage-grouse populations and habitat use patterns. Additional research is needed. Sagebrush Control Prescribed burning, as well as prescribed livestock grazing, herbicides and mechanical treatments, can be used to enhance sage-grouse habitat by purposely reducing sagebrush canopy cover where dense sagebrush canopy cover limits understory forbs and grasses. However, sagebrush thinning should be avoided where sage-grouse winter habitat is limited, and excessive removal of sagebrush cover may degrade sage-grouse nesting habitat. Sage-grouse and sagebrush rangeland ecosystems evolved with periodic fires that limited sagebrush canopy cover and restricted conifer encroachment. Management of both wild and prescribed fires is a key to maintaining sagebrush-dominated landscapes. Mean fire return intervals (i.e., the amount of time between fires on a site) of years are appropriate in mountainous sagebrush rangeland and year return intervals would be expected for drier, lower elevation sites. Fire can enhance native perennial forbs and grasses particularly in mountainous sagebrush rangelands and sage-grouse are attracted to burned areas during brood-rearing. In addition to fire, mechanical treatments and herbicides can also be used to control sagebrush or other woody species. When properly applied, herbicides inflict less damage to non-targeted plant species than mechanical treatments or fire. Livestock Grazing Livestock grazing may positively or negatively affect sage-grouse and sage-grouse habitat, depending on the timing and intensity of grazing. Heavy grazing (>60% utilization), especially during late spring and early summer, reduces the cover of perennial grasses and makes sage-grouse nests more vulnerable to predation. In contrast, light to moderate grazing in sagebrush rangeland is ecologically sustainable and can benefit sagegrouse. For example, sage-grouse prefer brood-rearing habitat where vegetation height has been reduced by moderate livestock grazing and sage grouse prefer areas where moderate livestock grazing has increased the 1 Prescribed livestock grazing is the careful application of grazing or browsing prescriptions (i.e., specified grazing intensities, times and frequencies, livestock grazing, and degrees of selectivity) to purposely sustain or enhance natural resources. 4

5 availability of succulent forbs. Prescribed livestock grazing also can be used to purposely enhance sagegrouse habitat. Examples include prescribed livestock grazing to control invasive weeds, suppress conifer encroachment, and reduce wildfire risks to sagebrush rangelands. Factors Other Than Habitat That Affect Sage-grouse Populations Predator Control As discussed earlier, the most common reason for sage-grouse nest failure is predation. Principal predators include coyotes, small mammals (e.g., skunks and ground squirrels), and some species of birds such as ravens and magpies. Changes in predator control policies and practices have allowed predator densities to increase dramatically during the past 60 years. Predator control may be needed to help recover some sage-grouse populations. Introduction of Nonnative Game Birds Gray partridge (also known as Hungarian partridge), chukar partridge, and ring-necked pheasants are all nonnative species of game birds that have been widely introduced in historic sage-grouse habitat. Although some of their habitat requirements throughout the year differ, there is at least the potential for competition, particularly during brood rearing when these species would use some of the same foods and are most likely to occupy similar habitats. More research is needed to examine potential effects, but displacement from former habitats and competition for food or cover may affect some sage-grouse populations. Dense sagebrush canopy cover lowers sage-grouse habitat quality and biological diversity. Sagebrush canopy cover should not exceed 15% on lower-elevation sites or 25% on mountainous sites. (Left Photo = 15% mountain big sagebrush canopy cover; Right Photo = 34% mountain sagebrush canopy cover). Photos courtesy of Jeff Mosley. 5

6 Landscape Issues It is apparent that rather than one, a few to many causes may be synergistically and cumulatively operating to diminish sage-grouse populations. For instance, reduced predator control may occur simultaneously with undesirable changes in vegetation structure triggered by other habitat management practices. It also appears evident that the causes of sage-grouse declines vary among different locations across the West. To focus only on one or two issues denies the complexity of the situation. Intermediate-sized landscapes of 615,000 to 6,200,000 acres seem to be the most appropriate scale for management solutions to be successful, since improvement in only one part of the year-round habitat could be negated by degradation in habitats needed during other seasons. Lasting solutions will come only when diverse groups of management and research professionals work together to improve and sustain sagebrush rangelands. It is not a process that will yield quick results. Time is needed to develop and implement management actions that produce or enhance the desired changes in habitat. It is imperative that such efforts begin as soon as possible. Sage-grouse do not thrive where large homogenous stands of any single plant species occupy the bulk of the landscape. However, the optimal or even tolerable proportions of seasonal habitats remain unknown. Only recently have analytical tools emerged to quantify habitat on landscape scales. Combined remote sensing, global positioning systems, and geographic information systems can be employed to provide both a visual and analytical description of large areas. Using archived imagery, these tools make it possible to analyze changes in geographic patterns over the past 50 years. Areas where sage-grouse have recently diminished should be analyzed. Another useful effort would be to compare landscapes holding non-migratory populations to those that are migratory. The existence of non-migratory populations implies that all habitat requirements of sagegrouse are sometimes met in one relatively small area. The mix of habitats and their proportions in those areas should be defined. Final Thoughts Today is not the first time that resource managers have been concerned about sage-grouse numbers and taken steps to recover sage-grouse populations. For example, due to concerns about declining sage-grouse populations during the 1930s and 1940s, several western states closed or severely restricted sage-grouse hunting seasons. Sage-grouse populations subsequently rebounded to relatively high numbers in the 1950s and 1960s only to be followed by declines from the 1970s to at least the 1990s. Since populations of sage-grouse have been known to vary significantly in the past, recent declines in sage-grouse do not automatically indicate that management of sagebrush rangelands must be radically changed. It is appropriate, however, to capitalize on opportunities to enhance sage-grouse populations and to In many areas, low sagebrush is also the primary habitat remain vigilant against new threats that may develop used for breeding. Photo courtesy of J. Meisel. 6

7 (e.g., sage-grouse mortality caused by West Nile Virus). Further conversion of sagebrush rangelands should be discouraged and maintenance or improvement in the health of the remaining sagebrush rangelands should become a higher priority. This will require more research, more and better focused monitoring and assessment, and the implementation of improved management within sagebrush ecosystems. Improved conservation and management of North American rangelands is one of the primary tools available to help stabilize and increase sage-grouse populations. Attempts Low sagebrush, where available, is important foraging to simply remove human influences from sagebrush habitat for hens prior to egg laying and for hens with broods during early brood- rearing because of the high ecosystems are not likely to be successful or result in availability of preferred forbs and insects. overwhelming improvements in sage-grouse populations. Photo courtesy of J. Meisel. Without purposeful habitat management (e.g., control of conifer encroachment, annual grasses, and noxious weeds), many sagebrush rangelands will not provide suitable habitat for sage-grouse. Improved management of sagebrush rangelands is key to improving sagegrouse populations. The Society for Range Management and its members remain dedicated to conserving and enhancing the world s rangelands to ensure that resources such as sage-grouse are sustained and will be enjoyed by future generations. This issue paper Ecology and Management of Sage-Grouse and Sage-Grouse Habitat is based on an invited synthesis paper by John A. Crawford, Rich A. Olson, Neil E. West, Jeffrey C. Mosley, Michael A. Schroeder, Tom D. Whitson, Richard F. Miller, Michael A. Gregg, and Chad S. Boyd published in the Journal of Range Management, 57:2-10, January Reference Information An Issue Paper by the Society for Range Management, W. 27th Avenue. Wheat Ridge, Colorado Phone FAX info@rangelands.org Internet: 7

8 For More Information: The Society for Range Management (SRM) is a professional and scientific organization whose members are concerned with studying, conserving, managing and sustaining the varied resources of rangelands. We invite you to contact us at: Society for Range Management W 27th Avenue Wheat Ridge, CO info@rangelands.org