JACKSON, Wyo. — Baby bluebirds are beginning to hatch in Jackson Hole!
Since mountain bluebirds (Sialia currucoides) are among the first nesting songbirds to return to the Greater Yellowstone area each spring, the initiation of egg laying can happen anytime between late April to early June.
Mountain bluebirds often socially mate for life, and will migrate back to their summer range early in the spring in order to secure a nest.
According to the U.S. Forest Service’s Mountain Bluebird Technical Conservation Assessment, male mountain bluebirds arrive to their breeding grounds in early spring, about one week prior to females. Males quickly establish territories around potential nest sites and are then visited by prospecting females. Once a pair-bond has formed, males spend a large proportion of their time mate-guarding, in an attempt to ensure paternity. Both sexes will readily attack same-sex intruders but not intruders of the opposite-sex.
According to the Avian Report, the timing of egg-laying is influenced by weather conditions and migration schedules. Spring storms and long periods of cold or heat influence the availability of food, disrupting the onset of nesting and egg-laying. Field observations indicate that wet and cold conditions during the beginning of the spring delay the breeding process.
Most eggs laid by female mountain bluebirds are pale blue. However, on rare occasions females lay pure white eggs. Typically, a female bluebird will lay one egg per day, usually in the morning, until clutch (the total number of eggs laid in one nesting attempt) completion. Clutch size varies from four to eight eggs.
The Jackson Hole Wildlife Foundation (JHWF) tracks bluebird reproduction in the valley in its effort to gauge overall ecosystem health. Every summer, volunteers monitor approximately 110 nest boxes once a week from April through July. Gathered data is entered into the Nature Mapping Jackson Hole database and given to the Cornell Lab of Ornithology as part of a nationwide effort to follow the impacts of climate change on bird species.
On Wednesday, May 22, JHWF shared a photo of the first mountain bluebird egg hatched in one of its nest boxes.
“We are expecting,” the Jackson Hole Wildlife Foundation posted via Facebook. “The first egg has been spotted in our bluebird trail nest boxes. This means a fledgling should be breaking into the world in approximately 12 days.”
Female mountain bluebirds sit on their eggs for approximately 13 days. During this time, the male provides the female with food. Typically all of the young hatch on the same day, but occasionally one young will hatch a day later.
Pairs will often attempt a second brood after successfully raising their first.
Be aware that during nesting season, both male and female bluebirds are extremely territorial. Typically, the male aggressively defends the edges of the territory, while the female tends to defend the area around the nest site. The birds will nest in hollow tree cavities and in bluebird houses provided by humans.
Do not touch bird eggs and/or nests, as this can possibly disrupt the breeding pair and the incubation period of the hatchlings.
