Bulls Believe Bigger is Better
The bull moose rocked his royal headgear from side to side, splintering branches as he responded to my grunt. The big bull was ready to defend the females in his harem from what he perceived to be another bull. Watching from a tree, I was thankful for two things: one, I wasn't on the ground; two, I wasn't a lesser moose on the ground.
In a moose's world, the big guys call the shots. Further proof of that comes from a new study by researchers at the University of Alaska's Institute of Arctic Biology. Graduate student Kelley Stewart and professor Terry Bowyer examined two groups of moose, one each in Alaska and Russia. They came away with some insights on how and why moose invest so much energy in antler development. In just a few summer months, moose antlers grow from tiny knobs to immense racks that weigh as much as 80 pounds. During June, the points on a moose's antlers grow more than one centimeter a day. One pound of antler can be added to a moose's head on one good day of growth Antlers are made of bone, which during growth is covered with furry brown velvet. Velvet, rich with blood vessels, nourishes the antlers until they stop growing and the bull scrapes the velvet off.
A male moose needs plenty of calcium and phosphorus during antler development. Most minerals come from willow shoots; some moose chew bones and antlers to increase their intake of minerals. The payoff for big antlers is worth gnawing a few bones. Dominant bull moose, the ones with the biggest racks, are the animals that assemble and defend harems of cows. They breed with the cows, passing on their genes, while smaller bulls wait in the wings for a chance to sneak in and mate with a dominant bull's cows. Bowyer said that's not a good strategy. "If they catch the little guy, they'll kill him," he said.
So what's a young moose to do? Stewart and Bowyer discovered that moose younger than about eight years old probably don't mate often. Their developing bodies need the minerals that a full-grown bull (about eight-to-11 years old) can invest directly in its antlers. Stewart said young moose would save energy if they didn't develop antlers, but perhaps they need them to spar with younger bulls and develop their pecking order. When a moose reaches full size and its body growth is complete, it can shunt most of its calcium and phosphorus into its antlers, perhaps even borrowing some from bones.
In the best-case scenario, a dominant bull avoids fights by intimidating other bulls by the sight of its rack alone. But another male of similar body and antler size forces even the biggest bull to fight. Bulls clash their antlers, knocking them together and pushing like sumo wrestlers until one backs down. The battles are extremely energy consumptive and sometimes fatal for the loser. The victor is often the one that invested ample energy into growing antlers but saved enough to develop a strong body.
