Restoration Plan for Sharp-tailed Grouse Recovery in Western Montana
Sharp-tailed grouse (Tympanuchus phasianellus) were once the most important upland game bird in Montana and occurred throughout much of the state, including grassland dominated mountain valleys west of the Continental Divide. However, western populations in Montana declined rapidly during the 19th century as Euro-Americans settled mountain valley habitats. Currently sharp-tailed grouse populations are widespread and stable east of the Divide but effectively extirpated in western Montana. This plan evaluates the potential for population recovery and outlines activities needed to restore a viable population of sharp-tailed grouse in western Montana.
Sharp-tailed grouse are the most widespread species of prairie-grouse (genus Tympanuchus), and occupy diverse grassland, steppe, and mixed-shrub ecosystems throughout central and northern North America. As a result, the species is thought to tolerate greater variation in plant community types and composition than other species of prairie-grouse. Plasticity in habitat utilization suggests high potential for successful translocations and reintroductions. Nevertheless, specific habitat requirements vary throughout the year; thus the availability and appropriate juxtaposition of key seasonal habitat components should be considered when selecting potential restoration sites. Within optimum sharp-tailed grouse habitat, large tracts of native grassland are maintained, mixed with areas of shrub cover, wooded draws, and some cropland. Relatively large, intact, and high quality native grassland or mixed-shrub habitats are required for nesting. Suitable nesting cover can be provided by herbaceous vegetation in more productive eastern ecosystems or a mix of shrub (e.g., sagebrush (Artemisia spp.)) and residual grass cover in dryer western ecosystems. Habitat edges, along with other areas transitioning from sparse to dense vegetation provide access to food resources in close proximity to escape cover and are often selected for by sharp-tailed grouse broods. Shrubby or woody areas, which provide thermal cover and food, are thought to become increasingly important to sharp-tailed grouse during the late fall and winter.
Habitat quality and quantity directly affect demographic performance of sharp-tailed grouse populations. The species has consistently high reproductive effort and a relatively fast life-history. Population sensitivity analyses indicate that reproductive success is one of the most influential demographic parameters affecting population dynamics. However, the timing and severity of weather events can also greatly influence overwinter survival and recruitment of birds to spring breeding populations. Thus management efforts to improve population performance should focus on nesting and brood-rearing habitats, followed by winter habitats. Within continuous grassland habitats, rangeland and grazing management is likely the most significant driver of habitat conditions and population performance. Management that provides compositionally and structurally diverse native grassland habitats with sufficient residual vegetation will improve reproductive success and survival.
To evaluate whether a viable population of reintroduced sharp-tailed grouse could exist in western Montana, we used life-history information from the published literature to conduct a population viability analysis (PVA). Our results suggest that under demographic rates that may result from existing habitat conditions, a population of sharp-tailed grouse in western Montana was not viable (i.e., did not have a 95% probability of persistence at 50 years post-establishment). However, a simulated management scenario where improvements to nesting and winter habitat increased fecundity and overwinter survival resulted in a viable population.
Assuming habitat improvements occur prior to translocations, a population composed of ≥ 280 individuals, and ideally ≥ 500 will be necessary to ensure population persistence over a 50-year period, which might be achieved through the translocation methods we describe. Environmental stochasticity had significant effects on 50-year population persistence and larger populations were more effective at recovering from random declines associated with annual environmental variability. The minimum amount of suitable habitat required to support a viable population was 4,340–7,750 ha, assuming habitat is sufficient to support an average density of 15.5 grouse per km.
All three potential restoration sites meet the minimum dynamic area needed to support a minimum population size of 280 birds. However, results of field-based habitat assessments indicate that the Blackfoot Valley site is the most similar to areas currently occupied by sharp-tailed grouse and should be the focus of initial sharp-tailed grouse habitat and population restoration. Several habitat enhancements that improve nesting and brood-rearing habitat and protect and enhance winter cover should be implemented prior to reintroducing sharp-tailed grouse to the Blackfoot Valley, including conifer removal, appropriate livestock management, and restoration of deciduous shrub habitats. Seasonal movements and space use can be large for sharp-tailed grouse, and cooperation among landowners and managers across large restoration areas will be needed for successful recovery.
Reintroductions of sharp-tailed grouse should follow protocols that minimize translocation-related mortalities, reduce movements away from the initial release sites, facilitate the quick establishments of leks, and assure sufficient genetic variation of founders to prevent genetic bottlenecks and inbreeding. Initial capture and translocation efforts should focus on establishing active leks with displaying males. Fall translocation of males has been shown to improve the probability of lek establishment and the likelihood of settlement by females released the following spring. Given the heavy mating skew of prairie-grouse, sex ratios of released birds should be 2 females to 1 male. The success of prairie-grouse reintroductions increases with the number of translocated birds and at least 100 birds (≥ 33 males; ≥ 66 females). Translocated birds should come from multiple source populations with similar environmental conditions, high fitness, and a similar evolutionary history to historic populations at reintroduction sites to minimize negative impacts to source populations and maximize genetic diversity. Periodic supplementation of additional females may be required if habitat connections with other populations cannot be re-established.