Gunnison Sage-Grouse

Gunnison Sage-Grouse (Centrocercus minimus)
 

male gunnison sage-grouse displaying

Gunnison Sage-Grouse male displaying.  © Noppadol Paothong

Since the late 1970's researchers became aware that the sage-grouse in the Gunnison Basin of Colorado were unique from sage-grouse found elsewhere in most of the United States. In 1995, Drs. Clait Braun and Jessica Young proposed that the Gunnison Sage-Grouse was a distinct species and, along with Drs. Jerry Hupp, Sara Oyler-McCance and Tom Quinn, they published their findings in the Wilson Bulletin (Young et al. 2000), for which they were awarded the Edward's Prize for the best major article published by that journal that year. The American Ornithologist's Union recognized the Gunnison Sage-Grouse as a newly named species in 2000, after a review of the scientific data by the AOU Nomenclature Committee, which consists of the leading taxonomic specialists in North and Central America.

Despite genetic, morphological, and behavioral differences, Gunnison Sage-Grouse and greater sage-grouse are believed to have similar life histories and habitat requirements. Most research about sage-grouse life history has been performed on greater sage-grouse, and while much of this research is applicable to Gunnison Sage-Grouse important differences exist between the two species.

Sage-Grouse are sagebrush obligate species; they require healthy, functioning sagebrush ecosystems for year round survival. Sage-grouse are also considered indicator species because, if the sagebrush habitat is not healthy, grouse populations also suffer. Due to high levels of natural variation in sagebrush community composition, grouse are adapted to a mosaic of habitats to support their annual cycle (Birds of North America). While most sage-grouse are non-migratory, some birds can move great distances to meet their dietary requirements and find their diverse seasonal habitats, (GUSG Range-wide Conservation Plan 2005). Adult Gunnison Sage-Grouse eat leafy vegetation and will also eat insects in summer. Although sagebrush leaves are their preferred food, grouse will also eat succulent forbs in summer. The winter diet is completely sagebrush based, requiring that some plants in winter habitat reach above the snow. Chicks consume insects and some forbs during brood rearing, and their diet shifts to sagebrush in fall (Birds of North America).

Annual survival rates vary: juvenile survival from hatch to fall is estimated to be 38 percent. Adult females have higher annual survival rates than males, possibly due to more cryptic plumage and secretive nature, compared to the males' elaborate plumage and display activities, (GUSG Range-wide Conservation Plan 2005). As birds age, the male to female sex ratio declines due to lower annual survival rates for males, (Birds of North America). Male survival rates are lowest during breeding season and female survival rates are lowest during nesting. Predators include golden eagles, a variety of hawks and accipiters, coyotes, red foxes, and bobcats. Nest predators include corvids, weasels, coyotes and badgers. Nest success is considered the most significant parameter influencing population dynamics, (Birds of North America).

Breeding

The sage-grouse annual cycle begins in mid-March, when the breeding season kicks off. Males congregate on leks, or strutting grounds, which are relatively bare, flat areas in the sagebrush ecosystem with good acoustic qualities and high visibility for females to assess the males' dance and vocalizations. These areas also allow for easy predator detection. Sites are usually located near good nesting habitat and good cover. Males begin to attend leks in early March; however, timing varies depending on snowmelt, weather, and photoperiod. Dominant males establish their position on the lek via wing fights and chases, usually trying to secure positions near the middle of the lek, (Birds of North America). Gunnison Sage-Grouse are highly philopatric, returning to exactly the same spot for generations, even displaying on the ice over the newly created Blue Mesa Reservoir where their lek had previously been, (National Park Conservation Association 2011, High Country News 2002). Males congregate to display for females from about an hour before dawn until about an hour after sunrise, with females showing up after males, and leaving while males are still displaying. Males typically do not move more than 1.5 miles from the lek during this time (GUSG Range-wide Conservation Plan 2005).

A lek system is polygamous, meaning females select which male to mate with and the male mates with several females. Approximately 70 percent of the copulations are by dominant males and only 10 to 15 percent of males actually breed, (Birds of North America, Gunnison Sage-Grouse Local Plan). This has significant conservation concerns because it reduces the effective population size (the number of individuals contributing genes to the next generation) below the absolute population size (the estimated total population) for males. It also limits genetic variation within the population. The lekking season runs from mid-March to late-May, with the highest lek attendance typically occurring in the second week of April. Females begin nesting as soon as they have bred, and the males provide no parental care.

Nesting

Nesting typically begins late April to the beginning of May; although, in early snow melt years females have laid their first eggs as early as mid-April, (Colorado Parks and Wildlife, unpublished data). Research has shown that 70 to 80 percent of nests occur within two miles of leks, however, female greater sage-grouse have been found nesting up to 20 miles from their mating lek, (Birds of North America). Quality nesting habitat requires live sagebrush with sufficient canopy cover to conceal the nest and a thick forb and grass understory. Often, high vegetative diversity provides the best horizontal and vertical cover, in turn providing greatest protection from visual predators and helping with thermoregulation, (Birds of North America, GUSG Range-wide Conservation Plan 2005).

Nests are shallow bowls lined with feathers and leaves at the base of live sagebrush. Clutch size averages seven to nine eggs, with yearling females having lower clutch sizes in some populations. Incubation starts once the last egg is laid and occurs for 27 to 28 days, (GUSG Range-wide Conservation Plan 2005).

Sage-grouse have some of the lowest nest success rates of all upland game birds, with success rates ranging from 10 to 63 percent for greater sage-grouse, (Birds of North America). Young (1994) reported a 43.2 percent nest success rate for Gunnison Sage-Grouse in the Gunnison Basin. Nest abandonment occurs in up to 22 percent of nests, and is most common when the female is disturbed by human activity, (Birds of North America). Re-nesting is infrequent but does occur, with typically lower clutch sizes.  Hatching begins in mid-May and usually ends by July, with peak hatch occurring between 10-20 June, (GUSG Range-wide Conservation Plan 2005).

Brood Rearing

Chicks are precocial and leave the nest with the hen within days of hatching. Hens with chicks move to areas containing succulent forbs and insects, often in wet meadows or riparian habitats where cover is tall enough to conceal the brood and provide shade. High quality brood rearing habitat is often classified as having high forb species richness, (GUSG Range-wide Conservation Plan 2005). Chick and juvenile survival depend on the availability of food and cover. Insects (primarily beetles, ants and grasshoppers) are the main food source for chicks during the first three weeks of life. From four to eight weeks old, the diet shifts to include plant material, including a variety of succulent forbs and some sagebrush, (GUSG Range-wide Conservation Plan 2005). After three months, sagebrush becomes the main dietary component. Adults will also eat some insects during spring and summer; however, forbs and sagebrush dominate their diet.

Unsuccessful nesting females and occasional males will join females with broods in these wet meadows, but are not as dependent on the habitat type. As autumn approaches, flocks and broods intermix as birds move from riparian areas to sagebrush dominated habitats that still provide some green forbs. Sometimes sage-grouse will move into agricultural fields at this time of year. Fringed sagebrush is a common transitional food as grouse shift from summer to winter diets, (Birds of North America).

Winter

Flock size in winter varies form 15 to 100 birds with flocks often made up of a single sex, (GUSG Range-wide Conservation Plan 2005). Many males overwinter within several miles from their lek. From the end of fall through early spring, sagebrush is almost the only component of sage-grouse diets. Almost any kind of sagebrush is consumed, though some birds select various subspecies for higher protein levels and lower monoterpene (plant defense chemical) levels, (GUSG Range-wide Conservation Plan 2005).  While birds may have low fat reserves after severe winters, individuals gain weight throughout most winters, (Birds of North America, Hupp and Braun 1989Beck and Braun 1978).  During harsh winters with high snow accumulation levels, grouse depend on very tall sagebrush that is exposed above the snow. In extreme winters, sage-grouse burrow into snow roosts for protection against the elements. Grouse may associate with ungulates that uncover sagebrush to browse on during the winter, (Birds of North America, Patterson 1952).

Gunnison Sage-Grouse have been documented moving as far as 17 miles to their winter habitat, but movements depend on severity of the winter, topography, and cover, (GUSG Range-wide Conservation Plan 2005).  Winter habitat requires tall sagebrush, such as that found on ridges, drainages, or southwest aspects.

The International Union for the Conservation of Nature (IUCN) recognizes the Gunnison Sage-Grouse as a red-listed, or globally endangered, species  (Storch 2007). In 2006, the Audubon Society listed the Gunnison Sage-Grouse as one of the 10 most endangered birds in North America. In January 2013, the USFWS proposed listing the species as an Endangered Species. In addition, they proposed 1.7 million acres of critical habitat for the species. On Nov. 12, 2014 the agency listed the Gunnison Sage-Grouse as "threatened" instead of "endangered" which is a more flexible protection status. For more information, visit the USFWS Gunnison Sage-Grouse website.

 Historic and Current Range

Historically, there has been a 90 percent or more loss in Gunnison Sage-Grouse habitat leading to the current distribution today, (Schroeder et al. 2004GUSG Range-wide Conservation Plan 2005). The Gunnison Sage-Grouse Range-wide Steering Committee estimates the historic range was 21,276 square miles and the current range is estimated to 1,822 square miles, which is 8.5 percent of the historic range, (Schroeder et al. 2004). Currently, Gunnison Sage-Grouse occur in six Colorado counties out of 22 that they historically occupied, (Braun et al. 2014). The estimated population sizes within each of the extant populations is a matter of significant concern. Only one population, the Gunnison Basin population, is estimated to have more than 500 individuals during the breeding season and that population contains more than 80 percent of all remaining individuals in the species. The remaining seven populations are isolated and small, with high male counts ranging from five to 42 males in recent years. Several populations have disappeared since 1980, (Braun 1995Young et al. 2000). 

The historic abundance prior to 1950 is unknown, but, based on historical documents and interviews, was likely orders of magnitude larger than present. Even during the past decades, lek areas in the Gunnison Basin have seen over 500 displaying males present. Currently, most leks in the Gunnison Basin have fewer than 50 males displaying and many have fewer than 20 males. Approximately 40 percent of the leks in the Gunnison Basin are classified as inactive and no longer have birds displaying on them. In other areas in the range, males have not attended leks for several years nor have new leks been discovered in adjacent areas.

Recent high male counts of males attending breeding grounds are provided courtesy of Colorado Parks and Wildlife (CPW). Current counts do not reflect the loss of birds from the 90 percent habitat loss calculated in the Gunnison Sage-Grouse Range-wide Conservation Plan, nor the inactive or extirpated leks in any population area. As the Gunnison Sage-grouse Range-wide Conservation Plan points out, lek data is most useful to determine long-term trends rather than population estimates. Sage-grouse populations and lek counts routinely vary from year to year. Comparing particular counts or lek areas can be useful to understand potential and percent decline in local areas. For example, in 1953, one lek area in the Gunnison Basin had over 500 birds attending it on a single day. A recent high count of that Ohio Creek area indicated an over 40 percent decline according to the Range-wide Conservation Plan. In other areas of the range, Gunnison Sage-Grouse have experienced greater than 90 percent declines on lek areas. Recent counts have highlighted concerns that population numbers in seven of the eight populations are becoming less sustainable and more vulnerable given low counts of males at leks. As mentioned above, there are also significant genetic diversity concerns associated with these small populations.

The counts displayed in the table above represent the high male counts (HMC) of males attending leks in the spring. Salmon colored cells indicate the lowest recorded HMC for that population, and green colored cells indicate the highest recorded HMC for that population. Note that, for the satellite populations, most of the lowest recorded counts occurred from 2009 to 2014 and most of the highest counts were recorded from 2001 to 2006. None of the populations has had its highest count since 2006. Lek count procedures were standardized in 1997, so prior count data was not included. There are two methods that have been used to estimate population sizes based on high male counts. The first estimate, found in most local conservation plans and used for the majority of greater sage-grouse populations, results in an overall spring estimate for the 2014 global Gunnison Sage-Grouse population of 3,852; the second method, found in the Gunnison Sage-Grouse Range-wide Conservation Plan, results in an estimate of 4,724.

Indicator Species

Wildlife agencies in the United States now recognize that Gunnison Sage-Grouse are indicator species for shrub-steppe habitat. An indicator species is one which, because of its unique life history and strong reliance to certain ecosystems, provides biologists with an indication of ecosystem health. These grouse are an ideal indicator species for uplands dominated by sagebrush (Young 1994). For example, they require a variety of habitats such as large expanses of sagebrush with a diversity of grasses and forbs and healthy riparian ecosystems. Their habitat requirements differ during most of the year and differ for sex and age classes. Therefore, the presence of each habitat type in healthy condition in close proximity to winter, lek, nest and brood-rearing habitat is essential. A large percent of each seasonal habitat must be in the later seral stages of ecological succession to meet the requirements of the grouse. If the sagebrush ecosystem is healthy (for example: the soil is stable with little accelerated soil erosion; ecological functioning is maintained with several trophic levels of nutrient cycling; and plant and animal communities are diverse and productive), then grouse populations and productivity will indicate the success of land use management. Surveying trends in land productivity and populations of grouse can be a useful management tool for assessing the sagebrush steppe-ecosystem health.

Habitat Loss and Fragmentation

The key to maintenance of any species is providing sufficient habitat. Some causes of habitat loss and fragmentation for Gunnison Sage-Grouse in the Gunnison Basin include: recreation, increased road density, the formation of Blue Mesa Reservoir, housing and urban developments, Uranium Mill Tailings Remedial Action, power lines and reduction of riparian areas. USFWS considers development and associated habitat fragmentation from roads, power lines and fencing to be the greatest threat Gunnison Sage-Grouse face. A second problem is the quality of existing habitat present. Some impacts which cause a decline in habitat quality are: excessive livestock grazing, drought, land treatments, increased elk and deer populations reducing shrub vigor and distribution, and herbicides. Increasingly, oil and gas exploration in the southwestern portion of the species range-wide is threatening habitat for breeding, nesting, and brood-rearing.

Female Gunnison Sage-Grouse are more likely to have a successful nest when vegetative cover is present. Loss of forbs and grasses can lead to increased risk of predation and decreased chances of success for young broods as they emerge from their nests.

Habitat Restoration

The Nature Conservancy is working with the Gunnison Climate Working Group to reduce the impacts of climate change on nature and people in the Gunnison Basin. The multi-agency collaborative group recently completed the first year of a climate adaptation project to build resilience in riparian and wetland habitats across the Basin. Since 2012, a proactive and energetic collaboration including restoration expert Bill Zeedyk, Colorado Parks and Wildlife, Bureau of Land Management, USDA Forest Service, The Nature Conservancy, Western Colorado University, along with landowners, partners and volunteers, built several hundred rock structures, called one rock dams, zuni bowls and media lunas along ephemeral streams on private and public lands. This collaborative project will help improve and restore Gunnison Sage-Grouse brood rearing habitat at a previously incised drainage.

Trap and Transplant Program

Colorado Parks and Wildlife began a trap and transplant program in 2009 to augment the satellite populations. Because the satellite populations have been declining for several years and are of significant conservation concern, the program began as a way to add birds to the struggling populations. It is also a way of increasing genetic diversity between the populations and preventing inbreeding. A sustainable number of birds are moved from the Gunnison Basin population to satellite populations every spring and fall.  Augmented satellite populations include Crawford, Dry Creek, Dove Creek, Poncha Pass and Pinyon Mesa.

Conservation Plans

The Gunnison Sage-Grouse Range-wide Conservation Plan, published in 2005, can be obtained from the Colorado Parks and Wildlifewebsite. Biologists from the following agencies contributed to the plan: Bureau of Land Management, Colorado Parks and Wildlife, National Park Service, Natural Resources Conservation Service, USDA Forest Service, U.S. Fish and Wildlife Service and the Utah Division of Wildlife Resources.

In the Gunnison Basin, Gunnison County has formed the Gunnison Basin Sage-grouse Strategic Committee which is a county sponsored board with diverse representation from federal and state natural resources agencies, the development, recreational, and environmental communities, the local stock growers, and Gunnison County. The group meets monthly and has worked on issues such as spring road closures, research projects, regulatory mechanisms to reduce impacts to sage-grouse, and development of CCAAs for private landowners and CCAs for public lands. They have also speared headed an 11 county coalition to increase proactive participation by county governments in Gunnison Sage-Grouse conservation efforts.

The local Gunnison Basin Sage-grouse Conservation Plan was published in 1997. Within the plan, specific conservation goals and objectives are proposed to restore habitat and population numbers of the Gunnison Sage-Grouse to the Gunnison Basin. In addition, over 50 conservation actions are proposed. Organizations involved with creating the plan include the Black Canyon Audubon Society, Bureau of Land Management, Colorado Parks and Wildlife, Gunnison County Stock Growers Association, Gunnison County, High Country Citizens Alliance, National Park Service, Natural Resource Conservation Service, USDA Forest Service, U.S. Fish and Wildlife Service, and Western Colorado University.

Each local working group (except Cerro-Cimarron-Sims) has created their own local conservation plan:

Links

Gunnison Sage-Grouse Specific Literature

Grouse Conservation Literature and Relevant Greater Sage-grouse Literature

Habitat and Sagebrush Management Literature