Fall in the Northern Hemisphere means rutting time for many ungulates. That includes those reigning giants of the deer world, the moose (known in Eurasia as "elk", not to be confused with the North American wapiti that goes by the same name).

Bull moose this season have romance on the brain – and fighting, too, if they happen to come across a counterpart with the same zealous focus that doesn't back down.

Two different moose battles have been caught on camera just recently in the US state of Colorado, home to around 1,000 Shiras moose, one of four North American subspecies.

On September 26, Theresa Willingham Bush filmed a bout in the southwestern part of the state near the town of Silverton. One bull wedges a rival's antler in his rack and forces him to the ground, and then drives his own tines into the felled opponent. Fortunately for his self-preservation, the losing moose manages to get up – and is promptly chased off.

Fights such as these can be very serious indeed: "extraordinarily violent", as veteran moose biologist Victor Van Ballenberghe noted in this this Denali National Park fact sheet, with a bull aiming "to twist an opponent's head, shove him backwards, cause him to fall, and gore him".

Heavy and broad-spreading, a bull moose's unique palmate antlers serve as formidable clashing weapons – their clatter may be audible from a mile away! – and their pointed tines can puncture eyes or flesh to dangerous effect. Battle-ready males during the rut sport thickened neck muscles for powering these jousting matches, as well as reinforced brows to protect against bony whacks, stabs and hooks. (Moose racks, as it turns out, are somewhat less effective against soccer nets, as some recent video from Alaska attests.)

Meanwhile, several hundred miles northeast, up the belt of the Colorado Rockies, a Blue River resident recently had front-row (or rather balcony-level) seats to a backyard moose contest. Though these bulls wear smaller antlers than the Silverton ones, this still has the hallmarks of a real battle rather than the comparatively easygoing sparring matches younger males often engage in. One bull is forced to the ground but regains his footing – only to be driven behind the homeowner's deck.

"I thought they were going to damage my deck," said homeowner wrote in a YouTube posting, "but luckily they didn't. The larger bull won and the smaller bull retreated and left."

The rut is an intense time for bulked-up, amped-up bull moose, which don't feed during the breeding season. Dominant bulls do their best to maintain control over groups of cows, and their mass and posturing are normally enough to discourage younger and/or smaller males from trying to challenge them. (In Van Bellenberghe's research in Denali, big high-ranking bulls accounted for nearly 90 percent of the actual mating in a given season.) As in many ungulates, all-out fights usually result from two similarly sized bulls that can't intimidate one another with antler heft or bearing alone, and decide to take the risk (worth it from a spreading-your-seed standpoint) and physically go at it.

Though the Shiras is the smallest of North America's moose varieties, bulls are still giants by any measure, weighing up to 540 kilograms (1,200 pounds). The biggest subspecies on the continent – and the biggest deer on the planet – is the Alaskan moose, clocking in at up to 816 kilograms (1,800 pounds) and wielding antlers more than two metres (6.5 feet) across.

Bull moose aren't just squaring off in the Southern Rocky Mountains, of course. Check out this fierce showdown recently filmed in the Gudbrand Valley of Norway, which clearly shows the trouble a bull faces if he's pushed off his hooves.



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