Eastern Bluebird Sialia Sialis; Western Bluebird Sialia Mexicana; Mountain Bluebird Sialia currucoides.
For birders (the preferred term, rather than “birdwatchers”) one of the positives of living in southern New Mexico is that the ranges of all three species of Bluebirds overlap in our area. To most people, the term Bluebird probably conjures up thoughts of summer. However, winter is when you will see them here.
How do you tell the difference between Eastern and Western Bluebirds? Both range in size from just over six inches to just over eight inches. So, they’re slightly smaller than their cousin, the American Robin, the most common North American Thrush (to which family Bluebirds also belong). Males of these two species appear very similar, but with a bit of practice, you can learn to distinguish them. Eastern Bluebirds sport bright royal blue upper parts, a rusty, orange-red chest, throat, shoulders and flanks, and bright white underparts. Western Bluebirds are a shinier, slightly darker blue above and have rusty reddish chests and flanks also. In contrast to their Eastern cousins, though, their throats are blue; they have a rusty patch on their backs; their cheeks are grayish and their underparts are blue to blueish gray.
The females of both species resemble drabber versions of the males. Eastern females are brownish to brownish gray above with a pale faded cinnamony wash on their chests, throats, and flanks and pale gray underparts. Female Westerns have a gray throat and belly, gray underparts, and a pale rufous wash across the breast. Both have blue highlights on the wings and tail, but on Western females they are duller and less extensive. Juvenile birds of both species resemble paler versions of adult females and have the typical juvenile Thrush spotting; on Easterns, the back and underparts; on Westerns, only the underparts.
Male Mountain Bluebirds are a bright cerulean or sky blue above, fading to a duller hue of the same color on their throat, chest and flanks, that shades to a pale gray on the rest of their underparts. The wings and tails of females are a faded version of the males’ sky blue, shot through with gray and grayish brown. Many females also show faint rusty tinging on their throats. Their heads and backs and are pale blueish gray, while their underparts shade to a paler gray dirty whitish. Juveniles have faint tinges of blue in their tails and are overall gray with extensive whitish spotting on their underparts.
In general, as their name implies, Mountain Bluebirds are found at higher elevations. Since our area is part of their winter range, and in winter many songbird species may move to lower elevations in search of food, it is possible to find them without going into the mountains. All three species prefer open habitat, be it riparian corridors, agricultural land, parkland or even (but less commonly) urban/suburban habitat with large numbers of trees.
This month, you can get out and look for Bluebirds, plus participate in an important citizen science survey. National Audubon Society (NAS) is projecting that due to climate change, suitable habitat for Western Bluebirds will decline significantly by about 2025. The Mesilla Valley Audubon Society (MVAS), your local NAS chapter, is participating in Bluebird surveys during the third week of January. If you’re interested in participating, contact C.J.Goin at either firstname.lastname@example.org or 202-1324.
The Bird of the Month feature is brought to you by the Mesilla Valley Audubon Society, the local chapter of the National Audubon Society. To learn about MVAS and its activities, including monthly fieldtrips and beginner bird walks, visit new-mexico-birds.com/