While we’re still shoveling snow and scraping windshields, bluebirds are thinking about spring. Colorado has three species of bluebirds, Eastern, Western (seen here) and Mountain, and all of them are what birders call “early nesters.”

Why do they arrive here so early in the year? Maybe it’s because they don’t travel very far for the winter. While other kinds of thrushes migrate to central America, bluebirds tend to stick closer to home.

Bluebirds living in the southern parts of the United States stay there year-round. Western Bluebirds from harsher climates winter along the Pacific coast or in the dry scrubland of the Southwest and Mexico. A few stay in Colorado.

Eastern Bluebirds spend the winter in the Southeast and along the Gulf of Mexico. Mountain Bluebirds in Alaska, Canada and the northern United States head for warmer areas, ranging from Utah, Colorado and western Kansas and Texas southward through Mexico. During migration, they are common along the Front Range.

Male bluebirds, like other thrushes, return to their summer range ahead of the females, so they can lay claim to a breeding territory. This area may be less than an acre to six acres or more, depending on how much food is found there. They will not take more space than they need, as it wastes their energy defending habitat they don’t use.

Male birds sing in the spring to advise other males that they will defend their territory. They aggressively drive away other males by prancing around, flicking their tail and wings, raising their crown feathers, and opening their beaks wide. This display is enough to convince the rival to leave, and actual fighting is usually avoided. Female birds do not establish territories, so they do not sing.

Once the male is established, he chooses a cavity in a tree as a potential nest site. It will be right in the middle of his territory. Bluebirds don’t make their own holes. They use ones that occur naturally, or that were made by woodpeckers. In a pinch, they will nest in the space between two large rocks.

When the females arrive, the male’s job is to convince a possible mate that his nest site is acceptable. He will fly in and out as if to say, “Hey, look at the great home I picked out for us!” Eventually a female will go inside and try it out. If she approves, she will be his mate for the entire season. (Next year, the male has to go through the whole process all over again!)

The female builds the nest and lays from five to eight eggs in it. Once they are all laid, she sits on them for approximately thirteen days until they hatch. She may briefly step out for a bite to eat, or her mate may bring her food.

At first, the fledglings are completely helpless. The female bird must keep them warm and fed. The male helps by delivering the food. They young birds eat so much that they double or triple their weight in the first week! The nest stays clean because the birds’ droppings come in a sac that the parents can carry away. After two weeks, the young have grown most of their feathers. Then they can learn to fly. They leave the nest during the third week.

A bluebird pair will usually raise two families per year. As soon as the first family is out of the nest, eggs are laid for the second family. After all the birds have fledged (have feathers and can fly), both families join together in one flock. They will stay together for the rest of the season, until they migrate. The male bluebird will guard his mate to keep other males away. They will both defend their nest from any threat. Nesting in a cavity helps keep the family safe from predators.

Over the next few weeks, I’ll be posting more information on bluebirds, and how you can welcome them into your yard.