Thursday, March 8, 2012

Dastardly Duos: Bluebirds

By Larry Liese
From the Vermilion Vaults
Originally appeared: Oct 2003 issue

Did you know that the ‘blue’ in bird’s feathers doesn’t come from pigment, as do most other colors? If you find a feather from a Steller’s Jay or other bird sporting blue colors, look at it closely and you’ll see that it has a darkish color that changes as you twist it to and fro. The blue colors we see on these birds is caused by structural properties of the feathers, with small irregular bodies in a transparent layer of the feather surface reflecting only blue wavelengths of light, while absorbing other wavelengths. Neat!

But for all that, our three bluebird species sure are blue! This month we’ll look at the females of two that are somewhat tricky to tell apart if the males aren’t about.

Here in southeast Arizona, the Eastern Bluebird (Sialia sialis) is an uncommon local permanent resident, found mainly in evergreen oaks and pines in the Huachuca, Chiricahua, Parajito and eastern Santa Rita mountains and sparsely in the Catalinas. They can also be found in the Patagonia area.

The Western Bluebird (Sialia mexicana) is more widespread but still an uncommon resident, with additional winter visitors making the bird fairly common in the cooler months, particularly where berries are available.

The males are fairly easy to tell apart. The western has a blue throat and bluish belly, with rusty scapulars; the eastern has an orange throat extending onto the sides of the neck and contrasting white belly and undertail coverts. The female eastern has that same contrasting white belly and orange on the sides of the neck, though the throat is white. The western female has a grayish-blue throat and a dusky belly color that does not show a sharp dividing line. Some western females will show a brownish patch on the back that contrasts with the nape, though some lack this.

Don’t be surprised if you have trouble when only females are present. There is much variation among individuals, and having a male come along and join a female after you make your call always helps (if you’ve guessed the right one, that is!).

Although pretty, bluebirds are pugnacious little creatures, and both male and female Eastern Bluebirds have been known to kill each other over mates and nest sites. Egad! So when you’re trying to tell these birds apart, don’t get in their way. Good luck!

1 comment:

  1. Great post! I've noticed both of the bluebirds all over lately.....they definitely are found in certain areas off of trails. My recent spotting was at Patagonia on the birding trail. Beautiful birds! Thank you for this useful information.

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