Bluebirds of San Diego County

Bluebird Nesting Behavior

Western Bluebird eggs by J. Dawsonhatchlings by J. Dawsonnestlings by J. Dawson

Courtship and Nest Building

The Western Bluebird (Sialia mexicana) sings repeated songs of "few" and calls of "chweer" or "che-check." Audible bill-snapping can occur during situations of alarm or aggression. During breeding season (late March to August) males will sing from a territory to attract a mate. When a female arrives, the male leads her to all the possible nesting locations that he has discovered within his territory. The female will examine each cavity and make the final choice. The male will sing and wing wave while she does this. He also feeds her bits of food. After she selects a site, the female will usually build the nest in about a week while the male guards her.

However, nests may be abandoned for many reasons; because one of the pair dies, there is a predator, another species takes over the box, or the bluebirds like it elsewhere.

Western Bluebird eggs by J. MorrisWestern Bluebird nestlings by J. Morris

Egg Laying and Incubation

Soon after the nest is finished, the female will begin laying one pale blue-white egg a day in the morning over the duration of about a week. After ALL of the eggs have been laid (usually 4-6), she then begins to incubate them for 13-14 days, taking breaks to go feed. During the week while the female bluebird is egg laying she spends very little time at the nestbox, so if you see eggs and no female around at this time do not conclude the nest is abandoned.

Female Western Bluebird by J. MorrisFemale Western Bluebird with nestling by J. Morris

Nestlings and Fledging

Once the young hatch, the female will brood them for about a week until they develop their feathers. Both parents feed them and remove the white fecal sacs to keep the nest clean. After about 19-24 days, the spotted young leave the nest and fly to nearby trees. The fledglings will be fed for a few weeks by the parents until they can catch food on their own. Western Bluebirds usually have two broods (occasionally three) during each breeding season from late March to the beginning of August. (Western Bluebird video depicting the nesting cycle.)

The first few months of a bluebird's life are the hardest and most dangerous, because they have little experience finding food and avoiding dangers. It is estimated that about 50 percent of fledglings do not make it through this stage. Those that do, live an average of 3 to 5 years, although lucky ones may live as long as 8 to 10 years.

Male and Juvenile Western Bluebirds by J. DaynesJuvenile Western Bluebird by J. Daynes

Window & Mirror Strikes

At the beginning of breeding season, bluebirds sometimes territorially strike at their own reflection in windows or car mirrors. They are attempting to defend their territory from a perceived rival bluebird. And since the "intruding" bluebird does not go away, the aggressive behavior continues to be stimulated. The best way to stop the behavior is to cover the window or mirror. Bird netting or shade cloth can temporarily be placed over outside windows, and socks can be placed over side-mirrors on parked cars. The behavior usually abates once the nest is well underway.