Sunday, January 4, 2009, 4:51pm
Ram Mountain in Alberta, Canada, is home to a population of bighorn sheep, whose most vulnerable individuals are males with thick, curving horns that give them a regal, Princess Leia look. In the course of 30 years of study, biologist Marco Festa-Bianchet of the University of Sherbrooke in Quebec found a roughly 25 percent decline in the size of these horns, and both male and female sheep getting smaller. There's no mystery on Ram Mountain: male sheep with big horns tend to be larger and produce larger offspring. During the fall rut, or breeding season, these alpha rams mate more than any other males, by winning fights or thwarting other males' access to their ewes. Their success, however, is contingent upon their surviving the two-month hunting season just before the rut, and in a strange way, they're competing against their horns. Around the age of 4, their horn size makes them legal game--several years before their reproductive peak. That means smaller-horned males get far more opportunity to mate.