Ruffed grouse, also known as partridge, are a medium-sized game bird found throughout the forests of North America. They are best known for the male’s elaborate courtship display that takes place in the fall. This display, called “drumming,” serves multiple purposes that help ensure successful mating and reproduction.
What is the drumming display?
The drumming display is an audio-visual show performed by male ruffed grouse in the fall to attract females for mating. It begins with the male standing on a prominent stage, usually a fallen log. He fans his tail into a semicircle and erects the feathers on his neck. The bird then begins rapidly beating his wings backwards to create a drumming sound. The beating wings create a vacuum, resulting in a throbbing noise as air rushes back in. This drumming sound can be heard from great distances. Drumming displays last from a few minutes up to 30 minutes.
In addition to the drumming sound, the visual component of fanning the tail and ruffled neck feathers adds to the display. Females are attracted by this multimodal exhibition, which serves to demonstrate the male’s fitness. Healthier males with greater stamina are able to drum longer and louder, signaling their genetic superiority.
Why do males display in the fall?
There are several reasons why ruffed grouse display their courtship rituals in the fall:
To attract females for mating
The main purpose of the fall drumming display is to attract females for breeding. Ruffed grouse have a promiscuous mating system where males mate with multiple females each season. Displays begin in late September and carry on through November. This timing coincides with the females’ peak fertility period before winter. By drumming, a male indicates his presence and fitness in hopes of securing as many mates as possible.
To identify territory
The drumming also serves to mark a male’s territory. Males return to the same display stages year after year. By drumming in traditional spots, they are defining their turf and warning competing males to stay away. Females take note of these landmarks when seeking a mate. The repetitive drumming deters intruders, communicating that the area is occupied by a dominant male.
To evaluate rivals
Males will often drum competitively in response to hearing a neighboring male. The back and forth drumming allows males to compare their fitness. Dominant, higher condition males are able to sustain longer and more frequent sessions. The interactive drumming matches help establish a hierarchy among males in an area. Females then have audible clues to assess potential mates.
To strengthen muscles
The vigorous wing flapping of drumming serves to strengthen a male’s flight muscles. In the wild, grouse rely on powerful escape flights from predators. Displaying increases muscular fitness ahead of the demanding winter season. The added exercise also keeps excess fat in check, maintaining an optimal body condition.
To reinforce social bonds
In addition to drumming alone, males will often assemble in groups called “drumming parties.” These gatherings with rival males facilitate social bonding outside of the breeding context. By drumming together, males learn the skills needed to attract females. Male offspring in particular can develop their techniques by observing their elders. The communal displays strengthen social relationships between males.
What are key features of fall drumming displays?
Some of the key features of ruffed grouse drumming displays in the fall include:
- Performed daily, most actively at dawn and dusk
- Last from a few minutes up to 30 minutes
- Males stand upright on fallen logs or rocky outcroppings
- Tail is fanned and neck feathers are erected
- Wings are beating forward and backward rapidly
- Creates a throbbing, drumming sound that carries over long distances
- Display areas are traditional, used yearly by generations of males
- Serves to attract females, ward off rivals, and strengthen flight muscles
How do environmental factors influence fall displays?
The drumming displays are dependent on certain environmental conditions. Here are some factors that play a role:
Elevation
Grouse occupy elevations ranging from sea level to tree line. Males at higher elevations commence drumming earlier in the season when compared to lowland areas. The onset varies by one week for every 700 feet gained in elevation. Early snowfall in the mountains accelerates the start of displays at high elevations.
Temperature
Drumming activity peaks when temperatures are between 38°F and 68°F. Grouse rarely display when temperatures exceed 80°F. Cool, sunny fall days following a frost are ideal drumming conditions. If temperatures drop below freezing, displays are inhibited though they may persist in brief daytime thaws.
Precipitation
Moisture strongly reduces drumming activity. Rainy or snowy weather prompts grouse to seek shelter. Dense fog also has an inhibiting effect. However, light morning dew does not impede drumming. Males regularly display on damp logs, suggesting moisture itself is not problematic.
Wind
Wind interferes with the acoustics of the drumming display. Males avoid drumming in excessively windy conditions where the sound would be drowned out. Light breezes under 10 mph do not seem to deter displays though the direction of the wind does impact how well the drumming carries.
Cloud Cover
Overcast skies have a marginal impact on drumming activity. While males prefer sunny conditions, they will display on all but the gloomiest days. Light to moderate cloud cover does not prevent displays, but may shorten their duration compared to clear skies.
Disturbance
Grouse are wary of human disturbance. Any disruptive noise, especially from loud machines, can halt drumming activity. Frequent passerby traffic on roads or trails also inhibits displays. Timber harvesting near display sites seriously interrupts the annual ritual.
How does drumming impact mating success?
The drumming display has an important influence on male mating success and reproduction. Some key outcomes include:
- Males that drum more have greater mating success
- Older males drum more often than younger males
- Dominant males drum for longer durations to deter rivals
- Females preferentially choose males that drum frequently
- Males with superior drumming sire more offspring
- Drumming is linked to higher testosterone in males
- Inferior drummers can be excluded from mating
In summary, drumming performance is a reliable indicator of male quality that females use in their mating selections. Males who can sustain longer, more persistent displays tend to have higher social status, experience, and reproductive fitness. The drumming allows females to discern these desirable traits when choosing their mates.
How do ruffed grouse benefit from fall breeding?
There are several advantages to ruffed grouse breeding in the fall season:
Abundant food resources
Fall is a time of plentiful food in the forest, like berries, seeds, and insect larvae. Good nutrition helps females produce more eggs and raise healthier chicks. Chicks also benefit from abundant food when hatching in the spring.
Mild weather
Fall weather is milder compared to winter or spring. The moderate temperatures reduce stress on breeding adults and are less demanding for newly hatched chicks. Wet spring weather increases risk of hypothermia.
Lower predation
Most predators reproduce in spring, increasing competition for fall-born chicks. By contrast, predator populations are at a seasonal low in the fall. This gives grouse chicks better odds of survival through winter.
No parasites
Parasites like mosquitoes and black flies that afflict grouse are absent in the fall. The lack of blood-feeding insects benefits breeding grouse and their offspring.
Vacant nesting sites
Spring-nesting songbirds have vacated their breeding territories by fall. The unoccupied sites offer more options for nest placement and reduced competition for nesting resources.
Longer development time
Chicks that hatch the following spring benefit from a longer period of development within the egg. This results in larger, stronger hatchlings compared to later spring nests.
Conclusion
In summary, ruffed grouse perform their characteristic drumming displays in the fall as a courtship ritual to attract mates. Males drum to advertise their presence, fitness, and territory ownership to females. Drumming also reinforces social bonds and helps males evaluate their competitors. Cool temperatures, light winds, and sunny conditions promote more active fall displays. By breeding in the fall, grouse benefit from plentiful food, mild weather, lower predation, no parasites, vacant nest sites, and extended egg development leading to healthier offspring. The drumming display and fall mating system are key adaptations that help ensure successful reproduction in this important game bird.