Category: Wildlife Research
Published: June 2004
Author(s): J. W. Connelly, S. T. Knick, M. A. Schroeder and S. J. Stiver
Greater sage-grouse (Centrocercus urophasianus) once occupied parts of 12 states within the western United States and 3 Canadian provinces. Populations of greater sage-grouse have undergone long-term population declines. The sagebrush (Artemisia spp.) habitats on which sage-grouse depend have experienced extensive alteration and loss. Consequently, concerns raised for the conservation and management of greater sage-grouse and their habitats have resulted in petitions to list greater sage-grouse under the Endangered Species Act. In this report, we assessed the ecological status and potential factors that influenced greater sage-grouse and sagebrush habitats across their entire distribution. We used a large-scale approach to identify regional patterns of habitat, disturbance, land use practices, and population trends. We included literature spanning the last 200 years, landscape information dating back 100 years, and population data collected over the last 60 years.
We described the primary issues that influenced greater sage-grouse and sagebrush habitats for an area that exceeded >2,000,000 km2 (>770,000 mi2) in size. To do this, we compiled, integrated, and analyzed data obtained from agencies and organizations within 14 states, >13 federal agencies, and 2 nations. We did not make recommendations or suggest management strategies. Rather, our goal was to present an unbiased and scientific documentation of dominant issues and their effects on greater sage-grouse populations and sagebrush habitats.
We organized the Conservation Assessment into 4 main sections. In the first section, (Chapters 1 and 2), we present background information on greater sage-grouse and sagebrush habitats. We first introduce the factors that have contributed to widespread concern about conservation and management of greater sage-grouse and sagebrush habitats. We also describe the historical and legal administration as well as the current stewardship of sagebrush habitats. We then provide information on the conservation status of the species across its range-wide distribution. The second section (Chapters 3-5) provides information on the basic ecology of greater sage-grouse and sagebrush habitats. Our objectives were to develop the underlying foundation on which to assess information presented in the remainder of the document. In the third section (Chapters 6-12), we describe the current situation and trends in greater sage-grouse populations and the dominant factors that individually and cumulatively influence sagebrush habitats. In the fourth section (Chapter 13), we integrate the habitat and population trend information into a synthesis of the conservation status for greater sage-grouse and sagebrush ecosystems in western North America.
Sagebrush ecosystems dominate approximately 480,000 km2 throughout western North America. Almost all (70%) of the existing sagebrush habitats are publicly owned and managed by a state or federal agency. The U.S. Bureau of Land Management is the primary agency responsible for management of public lands containing sagebrush and has stewardship for 50% of the sagebrush habitats in the United States. Multiple use is the dominant management objective on almost all sagebrush habitats.
Using a landscape perspective, we described the current status of sagebrush ecosystems (Chapter 5), trends within these systems (Chapter 7), and assessed impacts of anthropogenic change with respect to sage-grouse (Chapter 12). In most cases, we quantified the changes, the regional distribution of a factor, or the area influenced by the disturbance.
The sagebrush biome has changed since settlement by Europeans. The current distribution, composition and dynamics, and disturbance regimes of sagebrush ecosystems have been altered by interactions among disturbance, land use, and invasion of exotic plants. The primary areas in which sagebrush habitats currently cover a large regional portion of the landscape were in central Washington; southeastern Oregon, northern Nevada, and southwestern Idaho; and central Wyoming. Landscapes were highly fragmented surrounding these regions.
The number of fires and total area burned have increased across much of the sagebrush biome over the past 20 years (for which records are more reliable). Cheatgrass (Bromus tectorum) and other exotic plant species have invaded lower elevation sagebrush habitats across much of the western part of the biome, further exacerbating the role of fire in these systems. At higher elevations, juniper (Juniperus spp.) and pinyon (Pinus spp.) woodland invasions into sagebrush habitats also have altered disturbance regimes.
Land conversions were significant factors in separating habitat patches and fragmenting landscapes. Sage-grouse populations and sagebrush habitats that once were continuous now are separated by agriculture, urbanization, and development in the Snake River corridor in southern Idaho. Highly productive regions throughout the sagebrush biome that had deeper soils and higher precipitation have been converted to agriculture in contrast to the low elevation, more xeric climates that characterized the larger landscapes still dominated by sagebrush. Agriculture currently influences 56% of the Conservation Assessment Area and 49% of the sagebrush habitats by fragmenting the landscape or facilitating movements of potential predators, such as common ravens (Corvus corax) on greater sage-grouse.
Urbanization and increasing human populations throughout much of the sagebrush biome have resulted in an extensive network of roads, powerlines, railroads, and communications towers and an expanding influence on sagebrush habitats. Roads and other corridors promote the invasion of exotic plants, provide travel routes for predators, and facilitate human access into sagebrush habitats. Human-caused fires were closely related to existing roads. Less than 5% of the existing sagebrush habitats were >2.5 km from a mapped road.
We evaluated the influence of livestock grazing primarily by the effect on habitats resulting from management practices and habitat treatments. Numbers used by agencies (e.g., permitted Animal Unit Months) do not provide the information on management regime, habitat condition, or kind of livestock that can be used to assess the direct effects of livestock grazing at large regional scales. Indices of seral stage used to relate current conditions to potential climax vegetation may not correlate with current understanding of the state-and-transition dynamics of sagebrush habitats. Over half of the public lands have not been surveyed relative to standards and guidelines established for those lands. Although large treatments designed to remove sagebrush and increase forage palatable to livestock no longer are conducted, habitat manipulations, water developments, and fencing still are done to manage livestock grazing. Widespread water developments throughout sagebrush habitats increased the amount of area that can be grazed. More than 1,000 km of fences have been constructed each year on public lands from 1996 to 2002; linear density of fences exceeded 2 km/km2 in some regions of the sagebrush biome. Fences provide perches for raptors, and modify access and movements by humans and livestock, thus exerting a new mosaic of disturbance and use on the landscape.
Energy development for oil and gas influences sagebrush habitats by physical removal of habitat to construct well pads, roads, and pipelines. Indirect effects include habitat fragmentation and soil disturbance along roads, spread of exotic plants, and increased predation from raptors that have access to new perches for nesting and hunting. Noise disturbance from construction activities and vehicles also can disrupt sage-grouse breeding and nesting. Development of oil and gas resources will continue to be a significant influence on sagebrush habitats and sagegrouse because of advanced technological capability to access and develop reserves, high demand for oil and gas resources, and the large number of applications submitted (4,279 in fiscal year 2002) and approved each year.
Some land use factors that we considered, such as military training, may have very intense effects on habitats but are restricted to relatively small regions across the entire sagebrush biome. In contrast, livestock grazing influences sagebrush ecosystems across the entire biome. The cumulative impacts of the disturbances and the interactions among disturbance regime, invasive species, and land use have the most significant influence on the trajectory of sagebrush ecosystems rather than influences attributed to any single source.
Sage-grouse populations depend on relatively large expanses of sagebrush-dominated shrub steppe. However, the appropriate patch size needed for winter and breeding habitats used by greater sage-grouse is uncertain. It is likely that this patch size is not a fixed amount but depends on various factors including migration patterns and productivity of the habitat.
Greater Sage-grouse Populations
We describe the population biology (Chapter 3) and habitat needs (Chapter 4) of sagegrouse. Chapter 6 addresses sage-grouse databases, distribution, and population trends. We also review information on genetics (Chapter 8), hunting (Chapter 9), predation and disease (chapter 10) and current monitoring techniques (Chapter 11).
Sage-grouse are a relatively long-lived species of upland game bird with low reproductive rates. Sage-grouse are entirely dependent on sagebrush habitats for successful reproduction and winter survival. Disease and hunting have generally not been major factors in sage-grouse population change but new information suggests West Nile Virus may pose a significant threat.
All state and provincial fish and wildlife agencies monitor sage-grouse breeding populations annually, but monitoring techniques vary among areas and years both within and among agencies. This variation complicates attempts to understand grouse population trends and make comparisons among areas. However, virtually all states and provinces have increased monitoring efforts, especially over the last 10 years. Range-wide, population monitoring efforts increased by 737% between 1965 and 2003. The largest increases in effort occurred in Montana and Wyoming, two of the key sage-grouse states. Our analysis indicated that 2,637 leks are now censused annually.
We conducted a comprehensive analysis of sage-grouse population changes throughout their range by accumulating and analyzing all available male counts at 5,585 leks identified since agencies began routine monitoring of this species. We applied several different techniques to evaluate greater sage-grouse populations in North America. These techniques included: 1) changes in the average and median number of males per active lek; 2) changes in the average and median number of males per lek (including leks that are inactive); 3) annual changes in the number of males attending leks monitored in consecutive years (rate of change data); 4) evaluation of spatial patterns of lek extirpation; 5) evaluation of patterns of range extirpation; and 6) delineation and evaluation of distinct breeding populations.
The overall distribution of potential pre-settlement habitat was estimated to have been 1,200,483 km2 and the current distribution to be 668,412 km2. Approximately 56% of the potential pre-settlement distribution of habitat is currently occupied. The area currently occupied by sage-grouse is clearly smaller than was occupied in pre-settlement times.
With most of the analysis of sage-grouse numbers, we focused on the 1965-2003 period. Although many states and provinces were collecting data prior to 1965, this 39-year range provided an opportunity to analyze data after a sample of leks had been identified and protocols for data collection had been established and implemented. Eleven of 13 (85%) states and provinces showed significant long-term declines in size of active leks. Similarly, eight of 10 states (80%) showed population declines over the same time frame. Two of 10 (20%) appeared to be stable or slightly increasing. Only California had an increase in both the population index and lek size.
When sage-grouse breeding populations were delineated based on separation by distance and unsuitable habitat, trends for populations were similar to those of the states. Our analysis of the entire sage-grouse population indicated that sage-grouse declined dramatically from the 1960s to the mid-1980s and then tended to stabilize. This analysis indicated that these changes were often not density-independent. If trends characteristic of the 1960s through the mid-1980s continued, sage-grouse had a relatively high likelihood of being extirpated. However, those trends have not continued. As a result, data suggest sage-grouse populations in most areas have been relatively stable or slightly declining during the last 15-20 years. In many areas numbers increased between 1995 and 2003. Although there are areas that presently could be considered population strongholds, some populations are still declining rather precipitously in various portions of the species range.
Annual rates of change suggest a long-term decline for greater sage-grouse in western North America and support the trend information obtained from lek attendance (males/lek) data. Sage-grouse populations declined at an overall rate of 2.0% per year from 1965 to 2003. From 1965-85, the population declined at an average rate of 3.5%. From 1986 to 2003, the population declined at a lower rate of 0.4% and fluctuated around a level that was 5% lower than the 2003 population. A total of 50,566 male sage-grouse were counted on leks in 2003 throughout western North America. However, we are not optimistic about the future of sage-grouse because of long-term population declines coupled with continued loss and degradation of habitat and other factors (including West Nile Virus).
This report is the first detailed assessment of range-wide population and habitat data for greater sage-grouse. The information and analysis included in this report can be used to monitor future population changes and responses to management activities. As such, we hope that the information that we have presented now can be the foundation for increasing our understanding of the ecology of sagebrush-dominated landscapes and species that depend upon them.