The greater sage-grouse (Centrocercus urophasianus) is the largest grouse species in North America. It is known for its elaborate mating rituals that take place each spring on lek sites. Leks are communal breeding grounds where male sage-grouse gather to perform mating displays and court females. Understanding the sage-grouse’s mating behaviors and rituals provides important insights into this iconic western bird’s reproduction and conservation.
When Does Mating Season Occur?
The greater sage-grouse mating season occurs in early spring, typically from March through May each year. The timing coincides with the sagebrush flowering and green-up.
Mating starts as early as late February in southern portions of the sage-grouse range. In more northerly regions, peak mating can extend into early June. Weather patterns each spring impact exact lek attendance dates.
This seasonal timing allows young sage-grouse chicks the maximum time to grow and develop before the harsh winter months arrive again.
Where Do Sage-Grouse Mate?
Sage-grouse conduct their breeding activities on traditional lek sites. A lek is an open area surrounded by sagebrush where multiple male grouse display and compete for mates. Leks are typically on flat, open areas with good visibility, like ridges, meadows, or lakebeds.
Dominant male sage-grouse return to the same lek site year after year. Some lek locations have been used for over 100 years. There are records of leks over 200 acres in size. More commonly, leks span 1-40 acres.
The most attractive leks have dense female attendance. Studies show larger leks with more males result in increased breeding opportunities. Smaller satellite leks exist around main lek complexes.
How Do Males Prepare for Mating?
In preparation for the breeding season, male sage-grouse transition into their breeding plumage and begin congregating at lek sites.
Several weeks before mating gets underway, males start establishing individual territories on the lek. They defend these areas aggressively against other males with ritualized displays and fights.
Dominant males occupy central territories that offer the best acoustics and visibility for their courtship displays. Less dominant grouse get pushed to the peripheral zones.
Males perform vigorous exercises to strengthen the muscles required for their elaborate breeding displays. They may spend up to several hours a day exercising and perfecting their moves.
Physical Adaptations
Male sage-grouse undergo other physical changes in preparation for mating:
- Their yellow air sacs nearly double in size before mating starts.
- Featherless yellow-green aprons of skin develop on their chests.
- They shed and regrow their pointed retrices (tail feathers).
- Their overall size increases by up to 25% more than their winter mass.
These adaptations all facilitate effective visual displays to attract females. The male’s inflated air sacs, in particular, amplify and resonate the sounds he makes during his strutting displays.
What Do Sage-Grouse Lek Displays Look Like?
Each dawn during mating season, male sage-grouse gather at traditional lek sites and perform elaborate courtship displays called “strutting.” Their complex dances and vocalizations are meant to demonstrate fitness to females.
Dominant males occupy central territories on the lek where they perform “master cock” displays:
- They fan their pointed tail feathers upward and vigorously pump their bodies up and down.
- They rhythmically expand and contract the two large yellow air sacs on their chest.
- This creates dramatic “plopping” sounds as air is forced in and out.
- Their inflated air sacs and spread tail feathers create an impressive visual display.
As they strut, males also produce popping, hissing, and squeaking sounds. Their strutting displays can be heard up to a mile away on a calm morning.
The male’s airs sac displays pull in air from around the lek. This brings in the male’s scent to the attending females. His displays also demonstrate stamina and health.
Non-Dominant Males
Younger, subordinate males unable to claim central territories on the lek participate in moves called “chasing displays” along the edges:
- They run parallel to the central males.
- They fan their tails, puff their air sacs, and emit cackling sounds.
- They periodically rush towards the top males and attempt to jostle them.
These marginal males likely achieve occasional mating success when dominant males are distracted.
When and Where Do Females Come to the Leks?
Female greater sage-grouse arrive at the lek breeding grounds before dawn and quietly observe the male displays under cover of darkness. They may lurk 100-200 yards away in the sagebrush.
Females typically start visiting leks in early March, with peak female attendance in April. They tour multiple leks, carefully evaluating males at each site before selecting a mating partner.
Dominant central males on large leks perform nearly 85% of all successful copulations. These top males likely mate with 75-90% of all females breeding that season.
Females show a strong preference for mating with the most vigorous, fittest males with the most impressive displays. These males offer the best potential genes to ensure healthy offspring.
Receptive Females
When ready to mate, a female will approach one of the dominant strutting males directly on his territory. She crouches submissively before him with her wings lowered and tail fanned.
The male proceeds to mate with the receptive female. The actual mating act takes only a few seconds. Afterward, the female swiftly departs the lek and resumes her typical activities.
Timing of Visits
Females make dawn lek visits for only a week or two out of the entire two-month mating season. They usually attend in the hour before sunrise when male displays are at their peak.
A female generally mates just once per season, even though she may return to the leks multiple times to evaluate potential partners. She leaves immediately after mating.
Some females skip breeding in years when food is scarce to conserve resources. Other non-breeding females may still visit leks to assess potential future mates.
Do Males Care for Eggs or Young?
Male greater sage-grouse do not participate in parental care of eggs or young. Their role is purely to mate with females.
Some key points:
- A male sage-grouse’s involvement ends immediately after copulation.
- Different males mate with multiple females but provide no paternal care.
- Female sage-grouse raise their broods completely alone.
- Males do not defend females or offspring.
- Adult males may even compete with juvenile grouse for food resources.
The female alone selects a nest site, lays and incubates a clutch of 6-8 eggs for around 27 days, and raises the precocial young.
How Does Mating Success Vary for Males?
There is immense competition among male sage-grouse for mating opportunities on the lek. Dominant males achieve most copulations:
- Top males may mate with up to 75-90% of all fertile females.
- Some prime males breed with 20+ females in a season.
- Middle-ranked males get fewer chances to mate.
- Marginal subordinate males may never get to mate.
The most dominant strutting males are typically >4 years old with larger body size and more elaborate displays. Their prime breeding years are ages 5-8.
Males as young as 1-2 years old may gain a suboptimal lek position and mate with a few females. Aggressive encounters on the lek can injure young males.
The skewed mating success favors the evolution of the male sage-grouse’s elaborate physical and behavioral mating adaptations. Males with the fittest genetics tend to get selected year after year.
Mating Success and Genetics
Research shows male greater sage-grouse with higher genetic diversity have increased annual mating success.
Genetic diversity indicates overall health and fitness. Females seem to prefer males whose genetics indicate adaptability and resilience. Their offspring will inherit these favorable traits.
Dominant, high-fitness males pass on their genes much more frequently than lower ranking males. This maintains the genetic health of sage-grouse populations.
What Threats Do Sage-Grouse Face During Mating?
The elaborate mating rituals of the greater sage-grouse have occurred for centuries across the American West. However, sage-grouse now face multiple threats during the vulnerable breeding season:
- Habitat loss – Agricultural and urban development has claimed former nesting and brood-rearing grounds.
- Fragmented habitat – Remaining habitat is often fragmented, isolating leks and populations.
- Invasive plants – Cheatgrass and other invasive plants reduce native vegetation essential for feeding and shelter.
- Proximity to human activity – Noise, tall structures, roads, etc. near leks can disrupt breeding behaviors.
- Climate change – Altered seasonal weather patterns may affect lek timing and food availability.
- Predators – Land use changes have increased sage-grouse nest predation by animals like ravens.
Conservation efforts aim to protect key sagebrush habitat and lek sites. Maintaining connectivity across large landscapes is vital for sage-grouse populations to thrive.
Conclusion
The elaborate mating rituals of greater sage-grouse offer a fascinating window into their reproductive behaviors and biology. Male sage-grouse compete intensely each spring for dominance on communal lek breeding grounds.
Dominant central males perform elaborate strutting displays involving specialized air sacs, feathers, movements, and vocalizations. Their displays demonstrate health and fitness to visiting females.
Receptive females mate only briefly with select highly fit males. Powerful mating selection pressures drive the evolution of showy male forms and rituals.
Understanding these intricate mating traditions is key to conserving habitat and populations of greater sage-grouse into the future.
