A distant motor thud-thud-thuds as if trying to start, then dies
away. The noise repeats, and again dies off. I've been fooled by
this sound, wondering who could be trying to start a 2-cylinder
engine in the middle of the woods. This mechanical noise, of
course, is really the drumming of a male ruffed grouse.
People once thought that male grouse struck their wings on a
hollow log to produce this low whumping, but better observation
revealed something far more astonishing. The bird stands bolt
upright on a log, leans back on his tail, and fans his wings
vigorously - so fast, in fact, that the wings achieve the same
speed as the sound waves generated by their passage through the
air. This causes the sound waves to "pile up" into a penetrating
shock wave, also known as a sonic boom. For a
one-and-a-quarter-pound grouse to exert such force takes strength
and perseverance. Novice males have been observed going through all
the motions and not producing any sound at all.
With a bit of practice, you too can create a sonic boom. Take a
bull whip and flail with all your might. If you're lucky, you'll be
rewarded with an explosive crack. The whip moves in an up-and-down
series of waves along its length that undulate with increasing
speed as they approach the tip. By the time the wave motion reaches
the whip's end, the tip is moving at the speed of sound and the
crack is its sonic boom.
The rigors of drumming cause a male grouse to lose 10 percent of
his body weight during the spring season. So why, one might ask,
would a bird go to all this trouble? If you hadn't already guessed,
it's all to do with mating.
Grouse are secretive forest floor foragers that rely on cryptic
coloration and the cover of dense thickets to evade a long list of
predators, including foxes, coyotes, fishers, bobcats, owls, and
hawks. They live solitary lives for the most part. When it's time
to attract a mate, the male lacks a singing voice, and even if he
had flashy colors, they would be lost amid the vegetation. However,
the shock waves of drumming carry effectively through the
Drumming advertises the male's presence to female grouse. It is
also a territorial announcement that tells other males, "stay away
- this territory is taken!" In good habitat, male grouse tend to
space themselves so each defends an area of about 10 acres,
allowing them sufficient resources to survive. This space overlaps
the territories of several females that risk their safety in
walking some distance to investigate the drumming males.
Occasionally, less successful young males have been observed
drumming at the edges of a dominant male's performance area,
perhaps to take advantage of the influx of females. However, ruffed
grouse do not form the communal display areas (or leks)
characteristic of prairie grouse.
Loud self-advertisement is a risky business for a bird with many
enemies. The male grouse chooses his drumming site with care to
reduce the chances of predation. His performance stage, be it a log
(ideally 15 inches high and 20 to 40 feet long) or a rock, is
situated under overhead branches to deter raptors. At one end of
the stage is some form of escape cover, a root mass, some brush, or
a stump. The stage is usually in an area with a relatively
unobstructed view for 50 feet or more, so sneaking predators can be
spotted. Thus, a good drumming site is hard to find and once a male
grouse locates one, he tends to use it for life - that is, about
three or four years.
Mating, the reason for all this sound and fury, takes place in a
matter of seconds after a brief courtship in which the male struts
and fans out his tail and neck ruff. The female then disappears
back into the thickets, shouldering the perilous task of incubating
the eggs on the ground and raising the brood alone. If you see a
female grouse trailing her wing as if injured in the coming months,
she's bravely trying to lure you away from her chicks.
The male continues to drum for several weeks to attract more
females and mate with them. In autumn, he drums again, this time to
defend his territory from dispersing males.
To encourage grouse, encourage aspen. Dense expanses of aspen
saplings are preferred cover for grouse broods, while stands of
poles, eight to ten inches in diameter are perfect cover for
drumming males. Mature aspens provide buds and catkins, a critical
winter food of grouse. To keep up the supply of aspen, a
short-lived pioneer species, forests need a regime of periodic
disturbance. Forest fires, windstorms, and chainsaws can create
ideal grouse habitat.
Li Shen is an adjunct professor at
the Dartmouth Medical School and the chair of the Thetford,
Vermont, Conservation Commission. The illustration for this column
was drawn by Adelaide Tyrol. The Outside Story is assigned and
edited by Northern Woodlands magazine and sponsored by the Wellborn
Ecology Fund of New Hampshire Charitable Foundation.