Fall, Kenai Peninsula, Alaska
Moose are the largest deer in the world. The biggest moose of all live in Alaska, where males can top 1,700 pounds (770 kilograms) and grow antlers 6.8 feet (2.1 meters) wide. Female moose (left) are much smaller and lack antlers.
The striking differences between the sexes evolved primarily as a mating strategy. Big antlers signal to a female that a potential mate is of superior quality, which increases her chance of bearing a healthy calf. Males also evaluate antler size when deciding whether to fight over a female. Underequipped challengers will retreat, but equally matched bulls, like these, may battle.
Moose in Combat
Kenai Peninsula, Alaska
Two gigantic males clash for the right to mate with a female (left), interrupting the quiet of this Alaskan peat bog. Rival bulls will shove, clatter and twist their antlers, and even gore each other—sometimes for hours, and sometimes to the death.
Although the cow appears to be a bystander and have little choice in her mate, she actually can sway the outcome. By protesting loudly when courted by an undesired male, she can incite a fight involving the bull she prefers—a larger one who will likely win. The winner will snort in success as the loser retreats, and the victorious pair can then mate without further harassment.