Predators
Predators are commonly believed to negatively impact 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. Lack of adequate nesting and brooding cover may account for high juvenile losses in many regions. Nest success is related to herbaceous cover near the nest site. Taller, more dense herbaceous cover apparently reduces nest predation and likely increases early brood survival. Although predators were the proximate factor influencing nest loss, the ultimate cause may relate to the vegetation available to nesting sage-grouse. 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. 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 sage grouse 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 ten days in an area of significantly better cover (t test, P < 0.05).
Generally, quantity and quality of habitats used by 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.
A decline in preferred prey may also result in increased predation on sage grouse. Kindschy suggested that in southeastern Oregon, a decline in black-tailed jackrabbit (Lepus californicus) numbers may have caused predators to switch to sage grouse as their primary prey.
Predator species include coyote (Canis latrans), bobcat (Lynx rufus), American badger (Taxidea taxus), falcons (Falconidae), and hawks and eagles (Accipitridae) prey on adult and juvenile sage grouse. Crows and ravens (Corvus spp.) and magpies (Pica spp.) consume juvenile birds. Coyote, ground squirrels (Sciuridae spp.), and badger are the most important mammalian nest predators. Among bird species, magpies and ravens commonly prey on sage grouse nests.
Sage grouse are a popular game bird. Mortality due to hunting is generally considered to be compensatory and replacive, where until mortality reaches a "threshold value" it has no effect on population levels. Autenrieth and others state data are not available to suggest that closed or restricted hunting seasons will materially affect overall sage grouse population levels on their primary range.
In a study on hunting in a low density greater sage grouse population in Nevada, Stigar concluded low sage grouse populations may be a result of factors other than hunting. Protecting one sage grouse population from hunting while doubling the birds harvested in a four-year period on another population showed that despite low recruitment, both populations increased to nearly the same density. 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.
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