Thursday, December 11, 2008

Tricky ID #1: Eastern and Western Bluebirds

This is a big year for Western Bluebird in the Atascosa Highlands. It seems that every team has a good chance of seeing a bunch, and we could even surpass the record of 334 seen in 1980 (each team would have to see an average of only 17).

There will likely be a corresponding chance of getting a very large – but erroneous – number of Eastern Bluebird unless we are very careful of our IDs. Eastern Bluebird may be the most over-reported bird in southeastern Arizona by unwitting observers who simply look at the range maps and think the two species must be of equal status.

The reality is that Eastern Bluebird is one of the more local and sedentary southeastern Arizona specialties, our local subspecies being called "Azure Bluebird." They occur in only a very few areas in the southeastern corner of the state and with only some down-slope movement in some winters. Otherwise, they appear to remain in pairs or small family groups in the same small area all year. This is in strong contrast to Western Bluebirds which wander hundreds of miles in groups of sometimes dozens of birds. There are indeed records of flocks of Eastern Bluebirds in lower valleys every few years, but these appear to be irruptions from populations of the migratory eastern North American forms. It's a rare occurrence.

The only place in this CBC circle that I have seen Eastern Bluebird is at the Sycamore Canyon trailhead, and they are there almost every time I visit. There are surely more territories in the circle, and I would appreciate very much knowing where you find these. But please be sure you are identifying them correctly.

The voices are very different. Western Bluebird has a single, soft "whew" or doubled "weh-whew" whistle, also often mixed with a couple "chuck" notes or short rattle if perturbed. Eastern has a multisyllabic warble mixed with soft "chuck" notes.

Westerns will be in roving flocks, usually in mistletoe. Eastern will probably be only in a small groups or pairs.

Color is a clue in good light and views. The blue of our Easterns is really a bright azure blue. Western is a dark, luscious blue.

The pattern on the throat can be hard to discern in female and winter birds. If you don't see a blue throat, don't automatically assume that it's an Eastern. The throat color of Eastern will be either whitish in the female or bright orange in the male, but the key feature is that this orange color extends high on the sides of the neck and even curves up behind the ear covers. Western is uniformly blue or bluish gray on the sides of the head from the face down to the shoulder.

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