horns and antlers more than decoration

Bragging might be rude in the human world, but for a bull moose or a mountain sheep, it's part of the job.

by Claire Eamer

Bragging might be rude in the human world, but for a bull moose or a mountain sheep, it’s part of the job. Moose and sheep – along with animals such as pigs, horses, and camels- are ungulates, four-legged vegetarians that walk on

toes protected by tough hooves. They have some of the biggest weapons in the animal kingdom. And they flaunt them.

Consider the moose, the world’s largest living deer. A really big bull moose – and the Yukon has some big ones – can weigh as much as a polar bear and carry a set of antlers as wide as a king-size bed. Moose grow new antlers every year, starting in late spring. While they grow, they’re covered by soft skin, called velvet, which is full of blood vessels to nourish the antler bone. Early in fall, when the antlers are full-grown, the velvet starts peeling away. It’s the start of the mating season, or rut, and time to show off.

Braggarts in the forest

Yukon government moose biologist Rick Ward says the rut changes moose. “Bulls stop eating and lose considerable body mass. Testosterone levels rise, their necks and other muscle groups swell and bulk up, and the hide on their front quarters becomes thick and tough.”

Bull moose compete for the chance to mate with a cow moose. Sometimes they fight, but fighting is dangerous and uses a lot of energy. That’s where bragging and bullying come in.

The first brag is antler-thrashing. Male moose batter bushes and small trees with their antlers, cleaning off the last scraps of dried velvet and polishing the tines to sharp, white points. The broken bushes are markers that a big, tough bull is in the neighbourhood.

When a bull moose encounters another male, the real show begins. It’s called a dominance display. The bulls approach each other slowly, at an angle so that each can show off his enlarged muscles and swollen neck. With each heavy, dragging step, they tip their antlers from side to side. Often, they make low, rhythmic grunts or pause to thrash nearby trees. There’s plenty of time for a smaller male to decide he doesn’t have a chance and give in.

If the bulls are evenly matched, they fight. They clash antlers violently and push with all their weight and strength, ploughing up the ground with their hooves. The struggle goes on until the loser tries to disengage by turning away. He has to be quick to avoid being gored as he turns.

Avoiding unnecessary fights is worthwhile. Ungulate specialist Valerius Geist says active bulls receive 30 to 50 puncture wounds during the six-week rut.

 

Bullies on the mountain

For their size, mountain sheep are even more heavily armed than moose. A big ram weighs only about as much as a large man, but more than 10 per cent of that weight can be in the massive horns that sprout from its forehead. Yukon mountain sheep belong to the species called thinhorns, but that doesn’t mean their horns are puny. They’re just a bit thinner than those of the bighorn sheep that live farther south.

The horn is a hollow bone core surrounded by a sheath of keratin, a protein similar to the stuff in your fingernails. Sheep horns keep growing from year to year, curving as they get longer. By the time the ram is eight years old, his horns usually curl in a full circle on either side of his head.

The horns are rippled and ridged, with one thick ridge running the length of the outer edge. Geist says when a ram attacks, it rises up on its hind legs and jumps into the attack, flicking its horns forward so it hits with that ridge, with “the combined effect of a sledgehammer and a karate chop.”

Like moose, rams have ways of avoiding fights that they’re unlikely to win. They’ll pose sideways, head high, to look as big as possible, or make the opening moves of an attack to show they’re serious. Sometimes it takes a clash of the horns for one ram to decide the other is too strong to challenge.

“Rams have another behaviour that is quite neat,” says John Loehr, a Finland-based sheep biologist who has done much of his research in the Faro region. “They do something called a ‘low stretch’ where the displaying ram will lower his head and stretch it out as far forward as it goes and cruise past whoever he is trying to impress.” Usually the stretching ram is dominant, and the other ram will give way.

If neither ram concedes, the resulting fight can be bloody. Geist saw two evenly matched rams fight most of a day and into the night. “I heard clashes during the night,” he says. “In the gray light of dawn, two exhausted rams lay on a ledge, still displaying horn to one another.” The rams fought another five hours before one of the combatants finally gave up.

For more information about Yukon moose and sheep, go to the Environment Yukon website, www.env.gov.yk.ca,  or contact the Wildlife Viewing Program at wildlife.viewing@gov.yk.ca or 1-800-661-0408 local 8291 (toll free in the Yukon).

This column is co-ordinated by the Yukon Research Centre with major financial support from Environment Yukon and Yukon College. The articles are archived at www.taiga.net/yourYukon.