It takes a long time to raise a family of owlets, so the great horned owl begins early in the year. In January and February, or as late as March in the North, the male calls to the female with a resonant hoot. The female is larger than the male. She sometimes reaches a body length of twenty-two to twenty-four inches, with a wingspread up to fifty inches. To impress her, the male does a strange courtship dance. He bobs. He bows. He ruffles his feathers and hops around with an important air. He flutters from limb to limb and makes flying sorties into the air. Sometimes he returns with an offering of food. They Share the repast (食)after which she joins the dance, hopping and bobbing about as though keeping time to the heat of an inner drum. Owls are poor home builders. They prefer to nest in a large hollow in a tree or even to occupy the deserted nest of a hawk or crow. These structures are large and rough, built of sticks and bark and lined with leaves and feathers. Sometimes owls nest on a rocky ledge, or even on the bare ground. The mother lays two or three round, dull white eggs. Then she stoically settles herself on the nest and spreads her feather skirts about her to protect her precious charges from snow and cold. It is five weeks before the first downy white owlet peeks its way out of the shell. As the young birds feather out, they look like wise old men with their wide eyes and quizzical expressions. They clamor for food and keep the parents busy supplying mice, squirrels, rabbits, crayfish, and beetles. Later in the season baby crows are taken. Migrating songsters, waterfowl, and game birds all fall prey to the hungry family. It is nearly ten weeks before fledglings leave the nest to search for their own food. The parent birds weary of family life by November and drive the young owls away to establish hunting ranges of their own. What is the topic of this passage?