JACKSON, Wyo. — Baby bluebirds are beginning to hatch in Jackson Hole, and the Jackson Hole Wildlife Foundation (JHWF) is tracking their progress in its effort to gauge overall ecosystem health.
To help encourage the return of mountain bluebirds (Sialia currucoides) to the region in the spring, the JHWF, in partnership with the National Elk Refuge (NER), has continued to maintain and monitor a trail of nest boxes for the past 19 years. This “bluebird trail” consists of 110 to 112 nest boxes along 6.1 miles of NER fence on US89 from the NER & Greater Yellowstone Visitor Center to just north of the Gros Ventre River bridge.
Volunteers are assigned 5 to 10 boxes to monitor from May 1 through August 15. 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.
In 2024, approximately 22 volunteers monitored the nest boxes, which successfully fledged 78 mountain bluebirds, 135 tree swallows, five violet-green swallows and four northern house wrens, according to JHWF.
JHWF Nature Mapping JH Program Coordinator Jessie Walters told Buckrail that volunteers have spotted the first bluebird eggs of the season.
“We currently have 15 nests with eggs, however, there are nest boxes that have nesting material (grass, feathers, etc.) that do not have eggs as of yet,” Walters said.
Mountain bluebirds are among the first nesting songbirds to return to the Greater Yellowstone Ecosystem each spring, with the initiation of egg laying happening anytime between late April to early June. These song birds 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 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.
Walters said that bluebirds can have multiple clutches (the total number of eggs laid in one nesting attempt) of eggs in the same nest box, so monitors could see an increase in productive nests this summer. Pairs will often attempt a second brood after successfully raising their first.
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. 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 completion. Clutch size varies from four to eight eggs.
As part of the JHWF monitoring process, volunteers have color-banded 78 mountain bluebirds so far this year.
“In 2017, we began color-banding mountain bluebirds using these nest boxes to deepen our understanding of population trends, breeding site fidelity, survivorship and dispersal patterns,” JHWF wrote in its 2024 Annual Report.
According to Walters, nestlings have to be 9 to 11 days old in order to be banded. Once they are banded, volunteers will monitor from afar until the nestlings fledge, so they don’t leave the nest prematurely.
JHWF advises bird watchers to watch from a distance. People should not touch bird eggs and/or nests, as this can possibly disrupt the breeding pair and the incubation period of the hatchlings.
