Blue is an uncommon color in nature: blue pigments are chemically complex and costly for organisms to produce, and they’re not worth the expense for most organisms.
Among birds, however, it’s much less rare than in other organisms (birds can produce color in their feathers without chemical pigments, a phenomenon called structural coloration). This means that for most of us, a flash of blue is almost certain to be a bird – but which one?
Two of our most common blue birds are the Eastern Bluebird (Sialia sialis) and the Blue Jay (Cyanocitta cristata). At a glance, their dazzling blue wings and tails are easy to confuse, but there’s no need to dig out a field guide or app.
Although they have similar coloration, distinguishing these two species isn’t challenging. Differences in size, shape, coloring, and behavior set Bluebirds and Blue Jays apart, and once you know what these are, you’ll have no trouble telling them apart.
Distribution and Range
Eastern Bluebirds have a core range in the eastern United States, with some birds breeding as far north as southern Canada. In the northern half of their range, Bluebirds are seasonal migrants, and winter in Texas and the southeastern US, where breeding birds stay put year-round.
Blue Jays share most of their range with Eastern Bluebirds, but can also be found much further north, well into western Canada. Not all Blue Jays migrate, and when they do it’s not in response to falling temperatures, so most birders can expect to see at least some birds year-round.
Where their ranges overlap, the two species occupy distinct habitats. Bluebirds prefer open or semi-open country, and they’re commonly seen in meadows, along roadsides, and even on golf courses. Blue Jays are primarily woodland birds, but are quite adaptable, and are regularly seen in urban areas where Bluebirds are absent.
Diet and Behavior
Blue Jays and Bluebirds have markedly different life histories, which result from differences in diet. Eastern Bluebirds primarily are primarily insectivorous, while Blue Jays are true generalists: omnivorous, adaptable, and highly intelligent.
Bluebirds eat a wide range of insects and spiders, but in contrast to other insectivores like wood warblers (which glean their prey from trees) and flycatchers (which take insects on the wing).
Eastern Bluebirds catch their food on the ground, relying on keen eyesight to spot tiny movements in the grass. In the winter, they rely much more on fruits and seeds, and will often visit feeders that they would have disdained during breeding season.
The bulk of a Blue Jay’s diet is nuts and seeds, and acorns are a particular favorite. (In fact, the southward spread of oak trees since the last Ice Age is at least partially the work of Blue Jays.)
However, like most corvids – crows, ravens, etc. – they’re essentially omnivorous, and will eat anything from insects and lizards to carrion. Feeders are almost irresistibly attractive to them, and they will visit them at any time of year.
Size and Shape
The most obvious difference between Blue Jays and Eastern Bluebirds is size.
Bluebirds, at 16 to 21 cm in length (6 to 8 in), are shorter than Blue Jays (25 to 30 cm/9 to 12 in) – and at 28 to 30 grams in weight (1.1 oz), much less massive (Blue Jays average 70 to 100g/2.5 to 3.5 oz). To compare, a Bluebird is only a bit larger than a House Sparrow, while the Blue Jay is closer in size to a Mourning Dove or American Robin.
In addition to the difference in size, Blue Jays and Bluebirds are differently proportioned, giving them each a distinctive silhouette.
Blue Jays are long-legged and long-tailed, and their distinctive crests mark them out from other birds their size. Their broad, rounded wings are almost reminiscent of a hawk’s, and they fly with deliberate, steady wingbeats.
Bluebirds have more streamlined silhouettes than Blue Jays: they have small, flat heads, with small bills, and their legs and tail are much shorter relative to their bodies. Their wings are long and thin, with short primaries, which makes them much more agile flyers than Blue Jays.
Blue Jays and Eastern Bluebirds share vibrant, royal blue plumage that’s impossible to miss, and certainly the first thing you’re likely to notice about either bird. Look past this arresting first impression, though, and you’ll spot unmistakable differences in secondary coloring and pattern that set them apart.
Although they look monochromatic from a distance, Blue Jays are quite varied in their patterning. Their primaries and tail feathers are barred with black and iridescent patches, and their conspicuous crests are accentuated by a black collar ringing their faces.
Sexual dimorphism and seasonal variation are almost completely absent, and even young birds look essentially the same as adults – in short, a Blue Jay always looks like a Blue Jay.
Bluebirds share the Blue Jay’s general “blue above/white below” color scheme, but brick-red feathers on their throats and breasts contrast with their blue upper parts, extending under the wings and almost to the belly. Males are duller in the winter, while females and juveniles have less blue generally, and they often appear more gray than blue.
Blue Jays and Bluebirds share their arresting coloring, and are found in many of the same places, but they’re not difficult to tell apart. Different diets and habits mean that they aren’t often found in the same environment.
If size alone doesn’t distinguish them, their shapes and (non-blue) plumage surely will – so you can spend your time enjoying these beautiful birds, instead of puzzling over your field guide!