The great gray owl is North America's tallest owl and has the longest wingspan, although great horned owls are heavier. Great gray owls are mainly active during the day, especially when hunting food for their chicks during the summer months.
Great gray owls measure 24 to 33 inches in length and have a wingspan of 53 to 60 inches. They are gray-colored owls with round faces and large heads that lack ear tufts. Their eyes are small and yellow, and they have black-and-white markings under their faces that look similar to a bow tie. Great gray owls have very thick feathers that make them appear larger-bodied than they actually are.
Great gray owls prey chiefly on small mammals. These birds are largely sit-and-wait predators, but they may also fly slowly over an area to search for prey. They have excellent hearing and are able to detect prey by only sound. They can hear a rodent under nearly a foot of crusted snow, which they are capable of breaking through to reach prey.
Great gray owls are monogamous. Pairs re-use the nests of other large birds without adding any new material. The female lays two to five eggs that hatch in approximately 30 days, after which she broods the nestlings for up to three weeks while the male provides food. Owlets climb on branches and leaning trees as they learn to fly. Young owls typically fly within five to six weeks after hatching, although they receive parental care for three months.