Whirring and clapping wings play key roles in the displays of game birds
Published: March 1, 2005
|Bird courtship behaviors are fascinating. Typically they include both visual displays and vocalizations. Birds have a specialized structure called the syrinx that can produce sounds that range from simple call notes to the complex song of the Wood Thrush. Yet in some groups of birds, and especially among upland game birds, nonvocal sounds play critical roles in bringing the sexes together.|
Most grouse utilize sounds made by their feet and wings, and several have special resonating chambers called air sacs that amplify vocal sounds. Ruffed and Spruce Grouse display individually on their territories, while Sharp-tailed Grouse, sage-grouse, and the Greater Prairie-Chicken display on communal dance arenas known as leks.
The best-known nonvocal sound, perhaps, is made by male Ruffed Grouse. Their drumming is heard commonly in the early spring, although some birds drum at other times of the year. Males perch on a fallen tree or log, position themselves at a right-angle to the log, and spread their tail for support. Then the birds cup their wings and bring them forward and slightly up with great force. Air rushing into the vacuum created by the movement produces the sound.
Slow wingbeats create distinct thumps at first, then the drumming becomes progressively faster, ending in a muffled whir. The low frequency of the drumming (about 40 cycles per second) makes it difficult for listeners to pinpoint the actual distance and location. This is important because the Great Horned Owl, one of the grouse's natural predators, is thought not to hear below 60 cycles.
Like Ruffed Grouse, Spruce Grouse also display singly but are more difficult to observe because they occur in more northerly habitats and can display anywhere in their territory. A male attracts a female by flying up to a tree branch in a slow, noisy flutter flight. When a female becomes visible, he drops to the ground and approaches her slowly, making jerky, twisting movements that highlight contrasting color lines in his plumage. As the display continues and energy increases, the male pauses momentarily and quickly snaps his wings upward to near-horizontal two times, creating a soft pop, pop, before moving toward her again.
In the northern Rockies, a subspecies of the Spruce Grouse called Franklin's Grouse also utilizes a flutter flight to attract females. But rather than drop to the ground like the Spruce Grouse, Franklin's makes a long gliding flight that ends with two sharp wing claps.
Snapping to attention
Biologists long knew of the sounds but didn't know how they were made until they were recorded, synchronized with motion-picture film, and then slowed way down. What the film showed was remarkable: Late in the glide, the grouse momentarily stop their wings in a horizontal position before quickly snapping them up over their back, where they strike each other. The birds immediately drop their wings to horizontal again and then snap them upward a second time, making another sound. The claps can be incredibly loud.
Grouse that display on leks defend small territories within the arena. Older, more dominant males usually claim territories near the center of the lek, and they copulate with most of the females. Males display on their territories over boundary lines with rival males. Females that saunter through the lek select a mate, stop in his territory, and assume a receptive posture. If the male mounts her, rival males may try to knock him off.
Male prairie-chickens arrive on the leks before dawn. They lower their head, raise their tail, and dance rapidly, creating a drum-roll-like sound and spinning, sometimes in an irregular fashion, like a mechanical wind-up toy. Males face off across territory boundaries, and when challenged they often attack, using their beaks and claws. They frequently cackle, and at intervals, they stop dancing, lower their heads, expand their vocal sacs, and give a low-pitched sound similar to the one produced when you blow over a Coke bottle: va-vroooooooom.
The behavior is similar with Sharp-tailed Grouse, except that the vocalization of the Sharp-tailed lacks the amplified "booming" and the dancing is more rapid and intense. Native American dances are thought to have been influenced by dancing grouse.
The sage-grouse is tied to sagebrush habitat in the Northwest. They also dance, but at a lower intensity than the previous species. Their trademark display is strutting over their territory with tail raised and spread, revealing narrow, pointed tail feathers. Males beat their wings over raised feathers of the neck, making a swishing sound, and they create a loud vocal poink that is amplified by large paired vocal sacs. The two sounds are usually given in combination: swish, swish, poink.
The displays of all grouse are fascinating, but those of Sharp-tails and Franklin's blow me away. They're another testimony to the amazing behavior of birds.