Greater sage-grouse
| Greater sage-grouse | |
|---|---|
 | |
| Male in USA | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Subclass: | Neornithes |
| Infraclass: | Neognatha |
| Superorder: | Galloanserae |
| Order: | Galliformes |
| Family: | Phasianidae |
| Subfamily: | Tetraoninae |
| Genus: | Centrocercus |
| Species: | C. urophasianus |
| Binomial name | |
| Centrocercus urophasianus (Bonaparte, 1827) | |
| Subspecies | |
| |
 | |
| Sage grouse range[2] | |
The greater sage-grouse (Centrocercus urophasianus) is the largest grouse in North America. Its range is sagebrush country in the western United States and southern Alberta and Saskatchewan, Canada. It was known as simply the sage grouse until the Gunnison sage-grouse was recognized as a separate species in 2000.[3] The Mono Basin population of sage grouse may also be distinct.
The greater sage-grouse is a permanent resident in its breeding grounds but may move short distances to lower elevations duing winter. It makes use of a complex lek system in mating and nests on the ground under sagebrush or grass patches. It forages on the ground, mainly eating sagebrush but also other plants and insects. Greater sage-grouse do not have a muscular crop and are not able to digest hard seeds like other grouse.
The species is in decline across its range due to habitat loss and has been recognized as threatened or near threatened by several national and international organizations.
Contents
[show]Description[edit]
Adult greater sage-grouse have a long, pointed tail and legs with feathers to the toes. The adult male has a yellow patch over each eye, is grayish on top with a white breast, and has a dark brown throat and a black belly; two yellowish sacs on the neck are inflated during courtship display. The adult female is mottled gray-brown with a light brown throat and dark belly.
Distribution and habitat[edit]
Greater sage-grouse are obligate residents of the sagebrush (Artemisia spp.) ecosystem, usually inhabiting sagebrush-grassland or juniper (Juniperus spp.) sagebrush-grassland communities. Meadows surrounded by sagebrush may be used as feeding grounds.[4] Use of meadows with a crown cover of silver sagebrush (A. cana) is especially important in Nevada during the summer.[5]
Greater sage-grouse occur throughout the range of big sagebrush (A. tridentata), except on the periphery of big sagebrush distribution.[6] Greater Sage-Grouse prefer mountain big sagebrush (A. t. ssp. vaseyana) and Wyoming big sagebrush (A. t. ssp. wyomingensis) communities to basin big sagebrush (A. t. ssp. tridentata) communities.
Sagebrush cover types other than big sagebrush can fulfill greater sage-grouse habitat requirements; in fact, the grouse may prefer other sagebrush cover types to big sagebrush. Greater sage-grouse in Antelope Valley, California, for example, use black sagebrush (A. nova) cover types more often than the more common big sagebrush cover types.[7] Hens with broods on the National Antelope Refuge in Oregon were most frequently found (54–67% of observations) in low sagebrush (A. arbuscula) cover.[8] Desert shrub habitat may also be used by greater sage-grouse.[9]
Sagebrush communities supporting greater sage-grouse include silver sagebrush and fringed sagebrush (A. frigida).[10]
Their historic range spanned 16 American states and Alberta, British Columbia, and Saskatchewan in Canada. Between 1988 and 2012, the population declined by 98%.[11] By 2012, they were extirpated from British Columbia and left with only remnant populations in Alberta with 40 to 60 adult birds, and in Saskatchewan with only 55 to 80 adult birds. By 2013, sage grouse were also extirpated from five U.S. states.[11] In 2013, the Canadian Governor in Council on behalf of the Minister of the Environment, under the Species at Risk Act, annexed an emergency order for the protection of the greater sage-grouse.[11]
Ecology[edit]
Lek mating system[edit]
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Greater sage-grouse are notable for their elaborate courtship rituals. Each spring, males congregate in leks and perform a "strutting display". Groups of females observe these displays and select the most attractive males with which to mate. The dominant male located in the center of the lek typically copulates with around 80% of the females on the lek. Males perform in leks for several hours in the early morning and evening during the spring. Video Males gather in leks to court, usually in late February to April. only a few dominant males, usually two, breed. Sage grouse mating behaviors are complex.[4] After mating, the hen leaves the lek for the nesting grounds.
Open areas such as swales, irrigated fields, meadows, burns, roadsides, and areas with low, sparse sagebrush cover are used as leks.[14] Of 45 leks, 11 were on windswept ridges or exposed knolls, 10 were in flat sagebrush, seven were in bare openings, and the remaining 17 were on various other site types.[15] Leks are usually surrounded by areas with 20 to 50% sagebrush cover, with sagebrush no more than 1 ft (30.5 cm) tall.
Nest selection[edit]
Greater sage-grouse disperse to areas surrounding the leks for nesting.[16] In a study of habitat selection by male greater sage grouse in central Montana during breeding season, sagebrush height and canopy cover at 110 daytime feeding and loafing sites of cocks were recorded.[17] About 80% of the locations occurred in sagebrush with a canopy cover of 20–50%. In another Montana study,[18] sagebrush cover averaged 30% on a cock-use area, and no cocks were observed in areas of less than 10% canopy cover.
Some females probably travel between leks. In Mono County, California, the home range of marked females during one month of the breeding season was 750 to 875 acres (300–350 ha), enough area to include several active leks.[19]
Within a week to ten days following breeding, the hen builds a nest in the vicinity of the lek. Hens usually nest near the lekking grounds,[20] but some hens have been noted to fly as far as 20 miles (32 km) to favorable nesting sites.[21][22]
Quality of nesting habitat surrounding the lek is the most important factor in population success. Adequacy of cover is critical for nesting. Too little can exist: where 13% was the average total crown cover on Idaho range, nests were located where average cover was 17%. No hens nested in the most arid, open areas with less than 10% total shrub cover. Too much also can occur: average shrub cover at 87 nest sites was 18.4%, and in more dense cover, greater sage-grouse did not nest where total shrub cover was greater than 25%.[23] In Utah, no nests occurred where threetip sagebrush cover exceeded 35%.[10]
Sagebrush forms the nesting cover for most greater sage-grouse nests throughout the West, with concealment being the basic requirement.[24] Rabbitbrush (Chrysothamnus spp.) is occasionally used for nesting cover with greasewood (Sarcobatus vermiculatus) and shadscale (Atriplex canescens) being rarely used.[15]
Greater sage-grouse prefer relatively tall sagebrush with an open canopy for nesting. In Utah, 33% of 161 nests were under silver sagebrush that was 14 to 25 in (36–63 cm) tall, while big sagebrush of the same height accounted for 24% of nests.[10] In a threetip sagebrush (A. tripartata) habitat averaging 8 in (20 cm) in height, hens selected the tallest plants for nesting cover. Similarly in Wyoming, 92% of nests in Wyoming big sagebrush were in areas where vegetation was 10 to 20 in (25–51 cm) tall and cover did not exceed 50%.[15]
In Montana, when sagebrush characteristics around 31 successful and 10 unsuccessful nests were compared, successful nests had greater than average sagebrush cover surrounding the nest and were located in stands with a higher average canopy cover (27%) than unsuccessful nests (20%).[25] The average height of sagebrush cover over all nests was 15.9 in (40.4 cm) as compared to an average height of 9.2 in (23.4 cm) in adjacent areas.
During the nesting season, cocks and hens without nests use "relatively open" areas for feeding, and roost in "dense" patches of sagebrush.[14][23]
Brood rearing[edit]
Clutch size ranges from six to eight eggs; incubation time is 25 to 27 days. Greater sage-grouse apparently have high rates of nest desertion and nest predation.[4][26] Data from several sage grouse studies indicate a range of nesting success from 23.7 to 60.3%, with predation accounting for 26 to 76% of lost nests.[21]
Chicks fly by two weeks of age, although their movements are limited until they are two to three weeks old.[16] They can sustain flight by five to six weeks of age. Juveniles are relatively independent by the time they have completed their first molt at 10 to 12 weeks of age.[27]
Diet[edit]
Adults[edit]
The importance of sagebrush in the diet of adult greater sage-grouse is great; numerous studies have documented its year-round use.[6][7][16][15][14][24] A Montana study, based on 299 crop samples, showed that 62% of total food volume of the year was sagebrush. Between December and February, it was the only food item found in all crops. only between June and September did sagebrush constitute less than 60% of their diet.[16] Sage grouse select sagebrush species differentially. Greater sage-grouse in Antelope Valley, California, browsed black sagebrush more frequently than the more common big sagebrush.[7] The browse of black sagebrush is highly preferred by greater sage-grouse in Nevada. In southeastern Idaho, black sagebrush was preferred as forage.[28][29]
Among the big sagebrush subspecies, basin big sagebrush is less nutritious and higher in terpenes than either mountain or Wyoming big sagebrush. Sage grouse prefer the other two subspecies to basin big sagebrush.[30] In a common garden study done in Utah, greater sage-grouse preferred mountain big sagebrush over Wyoming and basin big sagebrush.[31] However, when leaves and buds of the preferred species became limited, the birds shifted to the lesser-liked plants. The birds, while expressing preference, are capable of shifting their eating habits.
Sage grouse lack a muscular gizzard and cannot grind and digest seeds; they must consume soft-tissue foods.[16] Apart from sagebrush, the adult diet consists largely of herbaceous leaves, which are used primarily in late spring and summer. Additionally, greater sage-grouse use perennial bunchgrasses for food.[32]
Sage grouse are highly selective grazers, choosing only a few plant genera. Dandelion (Taraxacum spp.), legumes (Fabaceae), yarrow (Achillea spp.) and wild lettuce (Lactuca spp.) account for most of their forb intake.[30] From July to September, dandelion comprised 45% of forb intake; sagebrush comprised 34%.[33] Collectively, dandelion, sagebrush, and two legume genera (Trifolium and Astragalus) contributed more than 90% of the greater sage-grouse diet. Insects are a minor diet item for adults. Insects comprised 2% of the adult diet in spring and fall and 9% in summer. Sagebrush made up 71% of the year-round diet.[34]
Females before laying[edit]
Herbaceous dicots are used heavily by females before egg laying and may be essential for their nutrition because of their high protein and nutrient content.[32]
Favored foods of prelaying and brood-rearing greater sage-grouse hens in Oregon are common dandelion (Taraxacum officinale), goatsbeard (Tragopogon dubius), western yarrow (Achillea millefolium), prickly lettuce (Lactuca serriola), and sego lily (Calochortus macrocarpus).[35]
Juveniles[edit]
In their first week of life, greater sage-grouse chicks consume primarily insects, especially ants and beetles.[15] Their diet then switches to forbs, with sagebrush gradually assuming primary importance. In a Utah study, forbs composed 54 to 60% of the summer diet of juveniles, while the diet of adult birds was 39 to 47% forbs.[36]
A Wyoming study evaluated effects of eliminating insects from the diet of newly hatched greater sage-grouse chicks. All chicks hatched in captivity and not provided insects died between the ages of 4 and 10 days, whereas all chicks fed insects survived the first 10 days. Captive chicks required insects for survival until they were at least three weeks old. Chicks more than three weeks old survived without insects, but their growth rates were lowered significantly, indicating insects were still required for normal growth after three weeks of age. As quantity of insects in the diet increased, survival and growth rates also increased up to 45 days, the length of the experiment.[37]
In a study conducted in Idaho, Klebenow and Gray measured food items for juvenile greater sage-grouse for each age class, classes being defined by weeks since birth. In the first week, insects were very important – 52% of the total diet. Beetles, primarily family Scarabaeidae, were the main food item. Beetles were taken by all other age classes of chicks, but in smaller amounts. All ages fed upon ants, and while the volume was generally low, ants were found in most of the crops. After week 3, insect volume dropped and stayed at a lower level throughout all the age classes, fluctuating but always under 25%.[38]
Forbs were the major plant food of the chicks. Harkness gilia (Leptosiphon harknessii) was the main forb species in the first week and then steadily decreased. It was not found in the diet after 6 weeks. Loco (Arabis convallarius) and common dandelion were important food items for most of the collection period and occurred with generally high frequencies. Common dandelion was the most abundant food item and the mainstay of the chicks. At 6 weeks of age, goatsbeard reached its peak in the diet and sego lily was found in greatest volume a week later. These five species were the most important forbs.
With plants like common dandelion and goatsbeard, all aboveground parts of the plant were sometimes eaten. The stems, however, were not of main importance. The reproductive parts, mainly buds, flowers, and capsules, were the only parts taken from some of the other species. Conversely, leaves were the only parts of sagebrush found in the crops. Leaves and flowers of the species listed above and other dicots contained higher amounts of crude protein, calcium, and phosphorus than sagebrush and may be important in greater sage-grouse diets for these reasons.[32]
Water[edit]
Greater sage-grouse apparently do not require open water for day-to-day survival if succulent vegetation is available. They use free water if it is available, however. Their distribution is apparently seasonally limited by water in some areas. In summer, greater sage-grouse in desert regions occur only near streams, springs, and water holes. In winter in Eden Valley, Wyoming, they have been observed regularly visiting partially frozen streams to drink from holes in the ice.[24]
Predators[edit]
Predators are commonly believed to reduce greater sage-grouse populations and of most importance is timing of death. Nest loss to predators is most important when potential production of young and recruitment are seriously impacted.[39] Lack of adequate nesting and brooding cover may account for high juvenile losses in many regions.[40] Nest success is related to herbaceous cover near the nest site.[26][41] Taller, more dense herbaceous cover apparently reduces nest predation and likely increases early brood survival.[39] Although predators were the proximate factor influencing nest loss, the ultimate cause may relate to the vegetation available to nesting grouse.[26] Tall, dense vegetation may provide visual, scent, and physical barriers between predators and nests of ground-nesting birds. Greater amounts of both tall grass and medium-height shrub cover were associated collectively with a lower probability of nest predation.[41] In a series of Nevada studies, artificial nest predation experiments were conducted. Artificial nests experienced 100% mortality with the loss of 1,400 eggs in 200 simulated nests in two weeks in one study, 84% of the nests were destroyed in three days in another study, while just 3% of the nests were destroyed in 10 days in an area of significantly better cover.[42]
Generally, quantity and quality of habitats used by greater sage-grouse control the degree of predation. Thus, predation would be expected to be most important as habitat size and herbaceous cover within sagebrush decreases.[39] A decline in preferred prey may also result in increased predation on greater sage-grouse. In southeastern Oregon, a decline in black-tailed jackrabbit (Lepus californicus) numbers may have caused predators to switch to greater sage-grouse as their primary prey.[40]
Predator species include coyote (Canis latrans),[40] bobcat (Lynx rufus), American badger (Taxidea taxus),[43] falcons (Falconidae),[44] and hawks and eagles (Accipitridae)[45] prey on adult and juveniles. Crows and ravens (Corvus spp.) and magpies (Pica spp.) consume juvenile birds.[40] Coyotes, ground squirrels (Sciuridae spp.), and badgers are the most important mammalian nest predators. Among bird species, magpies and ravens commonly prey on Greater Sage-Grouse nests.[16][27]
Greater sage-grouse are a popular game bird. Mortality due to hunting is generally considered to be compensatory[46][39] and replacive,[39] where until mortality reaches a "threshold value", it has no effect on population levels. Data are not available to suggest that closed or restricted hunting seasons will materially affect overall population levels on their primary range.[30]
In a study on hunting in a low-density greater sage-grouse population in Nevada, low populations may be a result of factors other than hunting. Protecting one greater sage-grouse population from hunting while doubling the birds harvested in a four-year period on another population showed, despite low recruitment, both populations increased to nearly the same density.[47] In an Oregon study, no relationship was found between the rate of summer recruitment (chicks/adult) and harvest by hunters, nor was any significant relationship found between the size of the fall harvest and population trends during the subsequent spring.[48]
Conservation[edit]
Residential building and energy development have caused the greater sage-grouse population to decline from 16 million 100 years ago to between 200,000 and 500,000 today.[49]
This species is in decline due to loss of habitat; the bird's range has shrunk in historical times, having been extirpated from British Columbia, Kansas, Nebraska, Oklahoma, Arizona, and New Mexico. Though the greater sage-grouse as a whole is not considered endangered by the IUCN, local populations may be in serious danger of extinction. In May 2000, the Canadian Species at Risk Act listed the Centrocercus urophasianus phaios, formerly found in British Columbia, as being extirpated in Canada.[50] The presence of subfossil bones at Conkling Cave and Shelter Cave in southern New Mexico show that the species was present south of its current range at the end of the last ice age, leading some experts to project that the species could become increasingly vulnerable as global climate change increases the humidity in semiarid regions.[51]
United States[edit]
In the United States, the species was a candidate for listing under the Endangered Species Act,[52][53] but the US Fish and Wildlife Service made a decision not to grant endangered species status in September 2015.[54]
A petition was signed by American Lands Alliance, Biodiversity Conservation Alliance, Center for Biological Diversity, Center for Native Ecosystems, Forest Guardians, the Fund for Animals, Gallatin Wildlife Association, Great Old Broads for Wilderness, Hells Canyon Preservation Council, The Larch Company, The Northwest Coalition for Alternatives to Pesticides, Northwest Ecosystem Alliance, Oregon Natural Desert Association, Oregon Natural Resources Council, Predator Defense Institute, Sierra Club, Sinapu, Western Fire Ecology Center, Western Watersheds Project, Wild Utah Project, and Wildlands CPR.[49]
In 2010, after a second review, the Department of the Interior assigned the greater sage-grouse a status known as "warranted but precluded", essentially putting it on a waiting list (behind more critically threatened species) for federal protection.
In April 2014, the Sage-Grouse and Endangered Species Conservation and Protection Act (H.R.4419)[55] was introduced in the U.S. House of Representatives to prohibit the federal government from listing sage grouse under the Endangered Species Act for 10 years, as long as states prepare and carry out plans to protect the species within their borders.[56][57]
Facing a court-ordered deadline of October 2015, the Department of the Interior on September 22, 2015, decided not to list the bird as threatened or endangered under the Endangered Species Act (ESA). As rationale for its decision, the Department said it would rely on a new land-management plan to protect the sage grouse’s habitat of 165 million acres across eleven Western states. The designation under the ESA would likely have led to land-use and other restrictions that critics feared would have economic impacts, possibly restricting oil and gas development and home-building. In issuing its finding, the FWS stated that:
"A status review conducted by the Service has found that the greater sage-grouse remains relatively abundant and well-distributed across the species’ 173-million acre range and does not face the risk of extinction now or in the foreseeable future.
The Service’s decision follows an unprecedented conservation partnership across the western United States that has significantly reduced threats to the greater sage-grouse across 90% of the species’ breeding habitat. The Service has determined that protection for the greater sage-grouse under the Endangered Species Act is no longer warranted and is withdrawing the species from the candidate species list.[58]"
Canada[edit]
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) designated the greater sage-grouse as Threatened in 1997, and re-designated the species as Endangered in April 1998.[59] The status was reevaluated and confirmed in May 2000 and April 2008. The greater sage-grouse is listed on Schedule 1 of Canada's Species at Risk Act, as Endangered.[60]
In 2013, the Canadian Governor in Council on behalf of the Minister of the Environment, under the Species at Risk Act, annexed an emergency order for the protection of the greater sage-grouse.[11][61][62] This order, among other things, prohibits killing of sagebrush plants, native grasses, or native forbs, and the building of fences and other structures in certain areas. The order is implemented "to protect a listed wildlife species on both federal and non-federal lands when the competent Minister is of the opinion that the species faces imminent threats to its survival or recovery."[11]
"Over the past several decades, Canada’s sage-grouse population has been reduced to remnant populations in Alberta and Saskatchewan. Historically, sage-grouse occurred in at least 16 states within the western U.S. and three provinces in Canada (Alberta, British Columbia, and Saskatchewan). Sage-grouse are now extirpated from British Columbia and five U.S. states. The sage-grouse population has continued to decline despite the provincial recovery strategies produced in 2001, 2006, and 2008. According to the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), between 1988 and 2012, the total Canadian population of the sage-grouse declined by 98%. Current provincial population estimates from 2012 in Alberta are 40 to 60 adult birds and 55 to 80 adult birds in Saskatchewan."
— Emergency Order for the Protection of the Greater Sage-Grouse 2013
In 2014, a ten-year captive breeding program for greater sage-grouse was initiated at the Calgary Zoo.[63] Despite only two of thirteen hatched birds surviving to the age of seven months, the program will proceed.[64]
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