North American Bluebirds: Which one are you seeing?

I keep seeing bluebirds on my commute to work, but I am not sure which of the three types of bluebirds it is.

If you are like me and ask yourself this question, this article is for you.

Knowing which of the three species of North American bluebirds is not difficult. All you need is to know about each species’ range and details of their plumage. Other identification keys such as size, habitat, and behavior are not very helpful.

Bluebirds have large ranges with relatively little overlap.

The mountain bluebird (Sialia currucoides), western bluebird (Sialia mexicana), and the eastern bluebird (Sialia sialis) have rather extensive geographic ranges. 

Mountain Bluebird               Western Bluebird            Eastern Bluebird

Range maps showing where each of the three bluebird species can be found. All species ranges are based on the information published in the Cornell Lab of Ornithology All About Birds.

Mountain Bluebird

The mountain bluebird has the second largest range. The wintering and breeding grounds include Alaska and Canadian provinces in the northern limit down to Central Mexico in the south. The eastern border can be visualized as an imaginary line between Montana’s Northwest Corner to western Texas. 

Western Bluebird

The western bluebird has the smallest range of the three bluebirds. The wintering and breeding grounds include the eastern corner of British Columbia south to central Mexico. The eastern border can be visualized as a line between Montana’s northeastern corner to Texas’ southwest corner.

Eastern Bluebird

The eastern bluebird is by far the most widespread North American Bluebird. Its huge geographic range extends from Canada’s southern provinces in the northern limit to as far south as Mexico and Honduras in Central America. The rocky mountains delineate the western border.

Overlapping range maps for mountain and western bluebirds.

Bluebird Range overlap.

Mountain and Western Bluebirds.

Bluebirds have parts of their ranges where only one species occurs. This makes things easier when figuring out the type of bluebird we see.

As shown in the map above, the mountain bluebird’s range is more extensive than that of the western bluebirds.

Mountain bluebirds occur throughout the western bluebird’s range, and it is the only bluebird beyond the range of the western bluebird.

The mountain bluebird is the only bluebird in most of Wyoming, Montana, Saskatchewan, Alberta, British Columbia, and part of the Northwest Territories, and Alaska. 

Both the mountain and western bluebird overlap ranges but telling them apart is easy due to their distinctive plumages.

Overlapping range maps for western and eastern bluebirds.

Western and Eastern Bluebirds.

These two similarly-looking bluebirds have largely non-overlapping ranges except for limited areas in the southern parts of their ranges. The eastern bluebird is the most widespread North American bluebird occupying more than the eastern half of North America and Central Mexico. Any bluebird you have in the states in tan (map) will be an eastern bluebird.

Interestingly, both bluebirds’ ranges overlap only during the non-breeding season of approximately October through February. This period corresponds to the time when bluebirds are generally migrating in semi-nomadic flocks of various sizes.

There is only one area in central Arizona, approximately in the Grand Canyon and west of Flagstaff, where both western and eastern bluebirds appear to stay and overlap year-round.

In conclusion, western and eastern bluebirds have largely non-overlapping ranges. If you are in the green range, you most likely see a western bluebird. Likewise, if you are in the tan range, you most likely see an eastern bluebird. Check twice at the bluebird you see in central Arizona and western Texas during October through February.

What about mountain and eastern bluebirds?

These two bluebirds have an even larger area of overlap than western and eastern bluebirds. Mountain and eastern bluebirds can be found together in northwest Texas, the eastern half of Arizona, eastern Utah, and western Colorado. These bluebirds overlap only during the non-breeding season of approximately October through February. This period corresponds to the period when birds are migrating in semi-nomadic flocks.

These two bluebirds’ plumage is rather distinctive and can be easily identified.

Bluebird Identification

Learning to identify bluebirds can achieve multiple benefits, beyond enabling us to know the species of bluebirds we see. Bluebirds have experienced changes in range and abundance, becoming rare where they once were common and vice versa. Accurate reports of our sightings can help detect population changes.

Can bluebirds be distinguished by size?

Size is generally a key field mark for bird identification. However, measures of length, weight, and wingspan of the three North American bluebird species are similar for use as reliable identification field marks. 

The table below shows the average length, weight, and wingspan for the three bluebirds found in North America. However, the range of measures for each metric in the three species has considerable overlap. Due to their similarity, measurements of size are an unreliable identification key to separate bluebirds.   

LengthWeightWingspan
Western Bluebird6.9 in0.95 oz12.4 in
Mountain Bluebird7.1 in1.1 oz12.6 in
Eastern Bluebird7.3 in1.1 oz11.2 in

What role does habitat play in identifying bluebirds?

Except for minor differences, bluebirds prefer open habitats with a variable number of trees and short, sparse ground cover.

Eastern bluebirds favor open habitats with short grass. Western bluebirds prefer open woodlands with a cover of grass or shrubs. Mountain bluebirds also prefer open habitats with scattered trees and a variable amount of vegetative ground cover. 

The similarity of bluebirds’ habitats makes it difficult to associate a bluebird species with a particular habitat type. Accordingly, habitat preference by bluebirds is an unreliable identification tool to help identify them.

Can behavior help identify bluebirds?

All three species of bluebirds have a somewhat stereotyped and similar foraging behavior. Bluebirds sit and wait on perches at various heights, scanning the ground below for a moving insect. Once prey is detected, the bluebird swoops to the ground to catch it.

The “sit and wait” foraging strategy is a relatively common one used by hawks, owls, flycatchers, and puffbirds. 

Bluebirds have favorite perches that they visit throughout the day. But there are areas without suitable perches that have the ideal ground cover conditions. Unlike western and eastern bluebirds that generally do not use these perchless areas, mountain bluebirds have solved this problem by hovering in mid-air while scanning the ground for prey. 

The hovering behavior sets mountain bluebird apart from its western and eastern counterparts.

Flocking

During the breeding season, bluebirds maintain a territory. A mated pair defends its territory from neighboring bluebirds. Once the breeding season is over, males and females join wintering flocks.

All three bluebirds exhibit similar behavior; therefore, the flocking behavior can not be used to help identify one species of bluebird from the others. 

Bluebirds can be identified by their plumage

Mountain Bluebird

Western Bluebird

Eastern Bluebird

Mountain Bluebird

The male mountain bluebird is entirely blue. The head and back are more saturated blue than the breast and belly, which has a whitish center.
The female mountain bluebird is mostly light gray with tinges of blue on the wing and tail. Some females are warm gray with brown breasts.

Western Bluebird

The male western bluebird has the entire head blue. The breast and flanks are orange. The back has a variable amount of chestnut-brown or orange. The folded wing is blue, and it is bordered by orange above and below. The center of the belly is whitish or bluish, maybe related to the bird’s age.

The female is a dull version of the male. The blue parts of the male are gray with tinges of blue in the female. This includes the entire gray head sharply set off from the reddish of the rich brown breast.

Eastern Bluebird

The male eastern bluebird has the top and sides of the head blue. The sides of the neck, throat, breast, and flanks are orange or red-brick. The back is entirely blue. The center of the belly is white.

The female is a dull version of the male, where the blue color is replaced by gray. The throat, breast, and flanks are warm brown. Females have tinges of blue on the lower back and tail and the primary flight feathers.

Conclusion: 

People often ask what kind of bluebird I see in my state.

Determining the species of bluebird you see in your state is relatively easy. 

Bluebirds have wide distributional ranges. Western and eastern bluebirds are similar in appearance, but their ranges have little overlap during the non-breeding season.

The mountain bluebird’s range overlaps with the ranges of both the western and, to a lesser extent, with that of the eastern bluebird. Fortunately, the mountain bluebird’s plumage is distinctive from eastern and western bluebirds and is unlikely to be confused.

All bluebirds are similar in size, use similar habitats, and exhibit similar behaviors.  These aspects are of little help to tell the species apart.

Knowing their geographic distribution and key differences in plumage will help you know which bluebird species you see in your state. 

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