By Rick Horton
The simple answer to the title question is: to better their chances for reproduction. In nature, one sex (typically the male) displays to potential mates that it is the fittest of its species. Females then select the fittest male for breeding, because they want their young to carry the best genes possible, thus increasing their chance of survival.
Males show their fitness in odd ways. In most cases, actual combat is avoided due to the risk of injury. Therefore they substitute scents, sounds, physical features, and behaviors that convey a threat to their rivals and show fitness to potential mates. They are usually defending some resource that shows the female that they can provide for them. Male birds may protect an area with choice nesting spots or select feeding locations. Wolves defend large territories with sufficient prey to provide for the pack.
Consider the case of bull moose. If two moose fight, a lot of ground will get torn up and somebody’s going to get hurt. So their first territorial defense is through scent marking. During breeding season, active bulls mark scent stations around their territory to let other bulls know to stay away and let females know he’s “open for business.” If a bull enters his territory, he uses his second line of defense – his antlers. In the deer world, large antlers convey the level of a male’s fitness. A smaller bull, upon seeing the large bull’s antlers, often decides he cannot win in battle and leaves the area.
If two bulls are closely matched, they may pose aggressively by erecting hair on their back and neck, standing stiff legged, dropping their ears, and showing off their antlers to make them look bigger. If all else fails and two bulls are closely matched, they do battle. But even the fights are not intended to harm one another, but rather are like big shoving matches. Whoever gets pushed around the most, leaves.
So why do grouse drum? Again, to defend their territory and attract a mate. While not as obvious as a moose, there are certain characteristics of a drumming log that make it attractive to females and convey to them that the defender of that log is the fittest male. Studies have shown that when a defender of a choice log is killed, lesser males from nearby “satellite” logs readily replace him. One log on the Cloquet Research Forest was continuously occupied for over 35 years!
The log is a stage where the male can beat his wings to produce sonic booms that carry through the dense forest. Females hearing the sound can find the male, assess his fitness, and decide whether to mate with him. Other males know the territory is occupied, but if they try to challenge him, he’ll puff up feather, hiss, charge, and fight if necessary. He’ll drum to announce his presence in any month of the year, but primarily in the spring breeding season and in September when young birds are dispersing and setting up their own territories.
Men wear cologne for much the same reasons as grouse and moose – to impress the opposite sex. Men are also known to puff up their chests and bluff their way out of fights!
Rick Horton is a forest wildlife biologist for the Ruffed Grouse Society, living in Grand Rapids, MN. For information about grouse or improving wildlife habitat on your property, he can be reached at 218-327-2524 or firstname.lastname@example.org.