North American has 3 species of bluebirds: Mountain, Western, and Eastern. Eastern Bluebirds can be found in Colorado, although they don’t often wander west of the eastern plains. One fun exception to this generalization occurred during a Christmas Bird Count in Salida one December. Much to our shock, we found 4 Eastern Bluebirds hanging around Frantz Lake! It’s unusual to find a Mountain Bluebird in central Colorado in the winter. Four Eastern Bluebirds was downright astonishing! Where they overlap, Mountain Bluebirds, which are a bit larger, generally dominate Eastern Bluebirds where they overlap. This fact may be a major limiting factor to the westward expansion of Eastern Bluebirds. However, Mountain and Western Bluebirds are pretty evenly matched and can be found in the same general areas during breeding season. Which happens here in central Colorado!
In case you’re wondering, male Eastern and Western Bluebirds look quite a bit alike. Easterns have white bellies and orange-red throats with solid blue backs; Westerns have blue throats and bellies and often have an orange-red patch that stretches to their backs.
Unlike many other thrushes, bluebirds aren’t known for their beautiful songs. You can hear clips of a Western Bluebird’s song and call here and a Mountain Bluebird song and call here. (Scroll down a bit to find the “typical voice” link.) Around our house, a soft, down-slurred whistle typ[ically alerts me to a Mountain Bluebird in the area. But I got a chance to hear the lovely, soft morning song of a Mountain Bluebird one morning. We got up at 3:45 a.m. (yes, that is not a typo) in order to run our Breeding Bird Survey route on Marshall Pass. (You need to be at the start of the route 1/2 hour before dawn, since birds are so much more vocally active around dawn.) I stepped outside around 4:15 a.m. and heard this lilting, almost whispered song from down the hill, where I knew a pair had a nest. What a delightful surprise! A tiny reward for being up well before the break of day…
Of all of the cavity nesters that use the nestboxes on our property, the Mountain Bluebirds tend to be the most aggressive and assertive during nestbox checks. Typically, as I approach a box, the female will zoom in–often very close to my head–and clap her beak at me. As I check the box, she often sits nearby and calls in the male. In fact, if I know there should be nestlings in the box and the female does not zoom in to watch me, I can be pretty sure that something has happened to her and this brood will be raised by the father alone. (If the nestlings are less than 8 days old, they generally will die without the female to keep them warm. Only the female has a brood patch–a bare, highly vascularized area of skin on her belly–that keeps the youngsters warm before they have their own feathers and can regulate their own body temperatures. Once they can thermo-regulate, the adult male can theoretically raise them by himself–but it’s an exhausting task for a single parent and often one or more nestlings die.)
Finally, click here to link to one of my favorite photos from our nestboxes.