While traveling across southern Utah last week my wife and I kept seeing momentary flickers of blue from some unknown bird. On our final day at Arches National Park we finally got a clear view of one of them. An argument between two males high in a juniper tree caught our attention, and I was able to get a few distant shots of this Mountain Bluebird (Passeriformes: Turdidae: Sialia currucoides).
Females are relatively drab-colored, sporting pale blue plumage only on their wing margins and tails. Males, in contrast, feature deeper blue coloration on their wings and tails, with light blue on their heads and chests. Since these birds inhabit sparsely-forested open areas of the west, however, females typically choose males based on the quality of their nests rather than their physical attributes. Males normally arrive at potential nesting sites early in the spring in order to secure nests from rival species like European Starlings and Tree Swallows. The males we witnessed in conflict may have been fighting for control of a desirable tree cavity that could be used to attract mates.
In warmer months Mountain Bluebirds use their relatively long, narrow beaks to pick off insects, spiders, and other arthropods. In colder months they often settle for the fruit of trees and other plants.
Although human activities have historically caused a slight decline in Mountain Bluebird populations, in more recent years humans have worked to help this species. Man-made nest boxes have provided supplemental nesting cavities these birds require for breeding, and bluebird populations are now relatively stable.