The greater sage grouse (Centrocercus urophasianus) and the Gunnison sage-grouse (Centrocercus minimus) are two closely related yet distinct species of large ground-dwelling birds found in sagebrush habitats across western North America. While they share several similarities and were once considered the same species, research over the past few decades has revealed important differences between the two sage-grouse that warrant their classification as separate species.
Physical Differences
The most noticeable physical difference between the greater and Gunnison sage-grouse is their size. As its name implies, the greater sage grouse is the larger of the two species. Males typically measure 25-29 inches long and weigh between 4-7 pounds. The smaller Gunnison sage-grouse males are around 17-20 inches in length and weigh approximately 2.5 pounds.
In addition to their overall size, the two sage-grouse can be distinguished by subtle differences in their plumage. Adult male greater sage grouse have white breasts and bellies and black abdomens, while Gunnison males have more solid grayish-white underparts. The filoplumes (slender display feathers) on the necks of greater males are also more elongated.
Key Physical Differences
Characteristic | Greater Sage-Grouse | Gunnison Sage-Grouse |
---|---|---|
Size | 25-29 inches long 4-7 lbs |
17-20 inches long ~2.5 lbs |
Male Plumage | White breast/belly Black abdomen |
Grayish-white underparts |
Male Neck Filoplumes | Elongated | Shorter |
Females of the two species are more difficult to distinguish visually. They share the same cryptic gray-brown plumage pattern. Female greater sage-grouse tend to be slightly larger and have more black barring on their undertail coverts.
Range and Habitat
The greater and Gunnison sage-grouse inhabit distinct but overlapping geographic ranges centered in different parts of the western United States. Greater sage-grouse have a wide distribution across sagebrush habitats in 11 western states and 2 Canadian provinces. Their range spans over 1,200,000 square km.
In contrast, Gunnison sage-grouse have a much smaller, more restricted range primarily concentrated in southwestern Colorado and southeastern Utah. They occupy an area of only about 8,500 square km. Historically, Gunnison sage-grouse also inhabited areas of northwestern New Mexico and northern Arizona, but populations in those regions have been extirpated.
Both species rely on large expanses of sagebrush for breeding, nesting, brood-rearing, wintering, and foraging. However, the two grouse tend to occupy slightly different sagebrush-dominated habitats and elevations within their ranges:
- Greater sage-grouse occur in sagebrush plains, foothills, and mountain valleys. They are found at elevations ranging from 4,000-9,000 ft.
- Gunnison sage-grouse live in lower elevation sagebrush flats, dry washes, and rolling hills at elevations between 6,000-8,000 ft.
Range and Habitat Differences
Characteristic | Greater Sage-Grouse | Gunnison Sage-Grouse |
---|---|---|
Range Size | ~1,200,000 sq km 11 western states & 2 Canadian provinces |
~8,500 sq km SW Colorado & SE Utah |
Key Habitats | Sagebrush plains, foothills, mountain valleys | Lower elevation sagebrush flats, dry washes, rolling hills |
Elevation | 4,000-9,000 ft | 6,000-8,000 ft |
Population Status
Both the greater and Gunnison sage-grouse have experienced concerning population declines over the past century. However, their current population statuses differ. The Gunnison sage-grouse is federally listed as a threatened species under the Endangered Species Act and is considered at high risk of extinction. Its total population is estimated at less than 5,000 individuals.
The greater sage-grouse is not federally listed but has been petitioned for listing several times. Its numbers have rebounded somewhat in recent decades after bottoming out in the 1990s. Current population estimates for greater sage-grouse range from 200,000 to 500,000 birds scattered across their range.
Habitat loss, degradation, and fragmentation due to human activities are the predominant threats facing both sage-grouse species. Energy development, agricultural conversion, urbanization, improper grazing, herbicide use, invasive species, and disease have cumulatively degraded and reduced sagebrush ecosystems. Additional threats include drought, severe winters, and climate change impacts.
Population Status Comparisons
Characteristic | Greater Sage-Grouse | Gunnison Sage-Grouse |
---|---|---|
Federal Status | Not listed | Threatened |
Population Estimate | 200,000-500,000 | <5,000 |
Population Trend | Rebounded from 1990s lows | Declining |
Behavioral Differences
The two sage-grouse exhibit some subtle differences in their breeding behaviors and displays. These variations likely contributed to their divergence into separate species.
One of the most conspicuous features of sage-grouse during the breeding season is the male display. Both perform an elaborate strutting display on communal breeding grounds where females congregate. However, greater sage-grouse have a more complex, drawn-out display sequence that involves motions such as bowing, wing-snapping, and popping tail feathers. The Gunnison display is shorter with a more pronounced bobbing motion.
The greater sage-grouse’s courtship displays also tend to be more vigorous and animated. They have been observed performing display flights around the breeding grounds, a behavior not typical of Gunnison sage-grouse. The differences suggest somewhat divergent mating strategies.
In terms of vocalizations, male Gunnison sage-grouse produce higher-pitched and more rapid popping sounds compared to the lower, slower pops made by male greater sage-grouse. Their calls likely evolved differently due to the habitats they occupy.
Both sage-grouse exhibit strong site fidelity to their breeding and seasonal grounds. However, some studies indicate Gunnison sage-grouse move shorter distances between seasonal ranges compared to greater sage-grouse. More research is still needed to confirm this potential difference.
Behavioral Difference Summary
Characteristic | Greater Sage-Grouse | Gunnison Sage-Grouse |
---|---|---|
Male Display | More elaborate, vigorous, animated | Shorter, more pronounced bobbing |
Male Vocalizations | Lower, slower pops | Higher-pitched rapid pops |
Seasonal Movements | Possibly longer distances | Possibly shorter distances |
Genetic Differences
Analysis of mitochondrial DNA and microsatellite data has revealed clear genetic distinctions between greater and Gunnison sage-grouse. Researchers have found less genetic diversity within the Gunnison sage-grouse population compared to greater sage-grouse. This indicates a long period of isolation and low levels of gene flow.
The two species are estimated to have diverged 150,000 to 500,000 years ago. Their separation was likely initiated during the Pleistocene Epoch when glacial advances fragmented the sagebrush-steppe habitat that their common ancestor occupied. This physical separation allowed the two populations to gradually evolve along independent trajectories into the distinct species recognized today.
While capable of interbreeding, greater and Gunnison sage-grouse do not produce viable or fertile offspring at high frequencies. There are very few known hybrid zones where the two species overlap geographically. Maintaining this genetic integrity is important for conservation.
Genetic Difference Highlights
Characteristic | Greater Sage-Grouse | Gunnison Sage-Grouse |
---|---|---|
Genetic Diversity | Higher | Lower |
Divergence | 150,000-500,000 years ago | 150,000-500,000 years ago |
Gene Flow | Some continued exchange | Very limited |
Hybrid Viability | Low fertility rates | Low fertility rates |
Conservation Implications
Recognizing greater and Gunnison sage-grouse as distinct species has important implications for their conservation. Each taxon faces unique threats and warrants individual management consideration. The Gunnison sage-grouse’s smaller population size and restricted range puts it at higher risk.
Tailored conservation strategies are needed to protect the key seasonal habitats, movement corridors, and lek sites required by each population. Particular focus should be placed on enhancing habitats degraded by human activity and restricting further development in priority areas.
Translocations from healthier greater sage-grouse populations may benefit declining Gunnison sage-grouse populations while minimizing risks of maladaptive hybridization. Captive breeding efforts should preserve genetic diversity in both species.
Further research is still required to better understand connectivity between populations, mortality factors, resilience to climate change, and other facets that will improve sagebrush ecosystem conservation and benefit both sage-grouse species.
Major Conservation Implications
- Requires management as separate species with distinct needs
- Gunnison sage-grouse is at higher risk and needs priority
- Protection of key seasonal habitats and movement corridors
- Restoration of degraded sagebrush ecosystems
- Regulation of further habitat destruction/fragmentation
- Strategic translocations and captive breeding recommended
- More research needed on populations, habitats, resilience, etc.
Conclusion
While the greater and Gunnison sage-grouse share close evolutionary ties and several similar habitat requirements and behaviors, scientific research supports their delineation as distinct species. Key differences in their size, plumage, range, genetics, displays, and conservation status provide a compelling case for evaluating each taxon separately. Continued efforts focused on preserving these iconic birds and the sagebrush ecosystems they depend on are crucial for ensuring their long-term persistence in western North America.