Birds

Bluebird

Sialia · also called bluebirds, eastern bluebird

Least Concern ↑ insectivoreomnivore Temperate grassland Temperate forest

A bluebird is a small thrush the colour of a clear sky, a fixture of North American fence lines and open fields, and one of conservation’s clearest success stories. By the 1960s it had nearly vanished from many areas, squeezed out of its nest holes by introduced birds. It was brought back not by governments but by tens of thousands of ordinary people putting up boxes.

Overview

Bluebirds are the three species of Sialia — eastern, western, and mountain — small thrushes of open and semi-open country across North America. They hunt insects by dropping from a low perch onto the ground, and switch to berries in winter. The blue is structural colour, not pigment: crush a feather and it turns grey-brown.

Cavity nesters in trouble

Bluebirds nest in holes but cannot dig their own, so they rely on old woodpecker holes, hollow fence posts, and boxes — and compete for them with the introduced house sparrow and European starling. Through the 20th century, as nest holes were cleared, pesticides cut insect food, and the introduced competitors spread, the eastern bluebird fell by an estimated 90 percent.

The bluebird trail

From the 1960s and 70s, groups such as the North American Bluebird Society promoted a standard nest-box design and encouraged people to set up monitored lines of boxes — bluebird trails — along farm fences and roadsides, removing sparrow and starling nests. Millions went up, and bluebird numbers climbed back to healthy levels.

Status

Least Concern and increasing — the eastern bluebird is now more numerous than a century ago. Ongoing pressures are sparrow and starling competition, loss of grassy habitat, hard late-spring storms, and pesticides.

Bluebird: common questions

How do I attract bluebirds to my garden?

The single most effective step is a properly built nest box, meaning a specific entrance hole size of around 38 to 40 millimetres for eastern and western bluebirds, no perch, mounted on a smooth pole about 1.5 metres up, facing an open grassy area, and fitted with a predator baffle. Place boxes away from dense buildings and heavy shrubbery, which favour house sparrows. Beyond that, keep some short grass with low perches for hunting, plant native berry shrubs for winter food, offer mealworms, provide a shallow water source, and avoid insecticides. In many areas a well-sited box is occupied within a season or two.

Why did bluebirds almost disappear?

Several pressures hit at once through the 20th century. The old wooden fence posts, dead orchard trees, and rail fences that provided nest holes were replaced with metal posts and cleared. Widespread pesticide use reduced the insects bluebirds feed their young. And two birds introduced from Europe, the house sparrow and the European starling, both aggressive cavity competitors, spread across the continent and evicted or killed bluebirds and took their nest sites. Eastern bluebird numbers fell by an estimated 90 percent, and the species became genuinely uncommon in many areas by the 1960s.

How did bluebirds recover?

Through a large, sustained, volunteer nest-box effort. Conservation groups, notably what became the North American Bluebird Society, promoted a standard box design and encouraged people to set up and monitor lines of boxes, called bluebird trails, along roadsides, farm fences, and field edges, and to remove house sparrow and starling nests from them. Millions of boxes went up. Combined with reduced use of the most harmful pesticides, this gave bluebirds the nest sites they had lost, and populations climbed back through the 1970s, 80s, and 90s to healthy levels.

What is the difference between a bluebird and a blue jay?

They are not closely related and are easy to tell apart. A bluebird is a small, plump, gentle thrush, about 16 to 18 centimetres, with a short straight bill, a rounded head, and a rusty-orange or, in the mountain bluebird, all-blue breast, and it sits quietly on low perches. A blue jay is a large, crested, noisy member of the crow family, around 28 centimetres, boldly patterned in blue, white, and black, with a heavy bill, and it is bold and often aggressive at feeders. If it is small, quiet, and orange-breasted it is a bluebird; if it is big, crested, and loud it is a jay.

Sources & further reading

Written by HideShark Editorial Team · reviewed by HideShark Science Desk. Published September 11, 2026. Last updated September 11, 2026.

Quick facts

Scientific name: Sialia
Diet: Chiefly insects and other invertebrates in the warmer months, grasshoppers, crickets, beetles, caterpillars, and spiders, taken by dropping from a low perch onto prey on the ground, switching in autumn and winter to berries and small fruit such as sumac, holly, mistletoe, and juniper
Three species: There are three bluebirds, all in the genus Sialia, the eastern bluebird across eastern North America, the western bluebird in the far west, and the mountain bluebird, a paler sky-blue bird of high open country in the west, and their ranges overlap in places
Structural blue: A bluebird's blue is not a pigment, since feathers with no blue pigment at all scatter light through a spongy nanostructure so that blue wavelengths bounce back, which is why a bluebird feather looks grey-brown if you crush it or hold it against the light
Hole-nesters that cannot dig holes: Bluebirds nest in cavities, old woodpecker holes, natural hollows, and nest boxes, but they cannot excavate their own, so they depend entirely on holes made by other animals or by people, and they compete for them with house sparrows, European starlings, tree swallows, and wrens
The bluebird crash: Eastern bluebird numbers fell sharply through the first two thirds of the 20th century, by some estimates by around 90 percent, as old orchards and wooden fence posts with nest holes were removed, pesticides cut insect food, and the introduced house sparrow and starling took over the cavities that remained
Saved by nest boxes: From the 1960s and 70s, organised campaigns encouraged people to put up bluebird nest boxes of the right size along fence lines and field edges, forming bluebird trails, and to control sparrows and starlings, and the bluebird populations recovered strongly and are now stable or increasing
A symbol of happiness: The bluebird has been a folk symbol of happiness and good fortune in North America for well over a century, appearing in songs, poems, and sayings such as the bluebird of happiness, which is part of why so many people were willing to build boxes for it
Range: North America, with the eastern bluebird from southern Canada through the eastern United States to Central America, the western bluebird along the Pacific states and the southwestern mountains into Mexico, and the mountain bluebird across the open high country of western North America from Alaska to Mexico, all favouring open and semi-open ground with short grass, scattered trees or posts to perch on, and cavities for nesting.
Conservation status: Least Concern ↑ ≈ All three bluebirds are now common and assessed as Least Concern, and the eastern bluebird in particular has increased steadily since the 1960s and is more numerous than it was a century ago, a genuine conservation success driven largely by volunteers maintaining nest boxes. Remaining pressures include continued competition from house sparrows and starlings, loss of open grassy habitat with scattered perches, severe cold snaps and late storms that can kill birds and broods, and pesticide use that reduces the insect supply. The western and mountain bluebirds are also stable, though local populations fluctuate with weather and habitat change in the wild