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 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.