Eastern Bluebird, Sialia sialis
Eastern Bluebird, Sialia sialis. Photograph taken within the Reserva Monte Mojino, Alamos, Sonora, December 2017. Photograph and identification courtesy of David F Smith, Alamos, Sonora.
Eastern Bluebird, Sialia sialis. Photograph taken within a residential community in Hereford, Arizona, June 2016. Photograph and identification courtesy of Karen LeMay, Sierra Vista, Arizona (naturewideimages.com).
Background and Identification
The Eastern Bluebird, Sialia Sialis, is a member of the Mimidae Family of Mockingbirds and Thrashers. This species is known for its blue and rusty plumage and abundance in heavily populated areas. Eastern Bluebirds readily take to artificial nesting sites and often nest in disturbed areas, such as construction and other developing urban areas. Humans frequently study the Eastern Bluebird because it uses artificial nesting cavities and exhibits open-area foraging behavior.
The Eastern Bluebird is a small thrush with an average overall length of 16 cm (6.3 inches) to 21 cm (8.3 inches) and an average mass of 28 g (1.00 oz) to 32 g (1.13 oz). This species is sexually dimorphic, males are more vividly colored than females. Males have deep blue wings and a bright orange throat and belly. Females, while sharing the same basic plumage pattern as males, have a more subdued blue-grey coloring. Both sexes have a white belly and a somewhat rounded, slim body, typical for many thrushes. Bluebird sex is easily determined by humans, but even easier to determine between conspecifics and other bird species. Conspecifics are defined as individuals of the same species. Unlike humans, bluebirds and most other birds can see into the Ultraviolet (UV) range of colors. This allows them to see the reflection of UV light in the plumage of other individuals and from recent studies, we know that bluebird males reflect more strongly in the UV spectrum than the females. Juvenile plumage is browner, but males still have blue feathers on their wings and tail, making sexual differentiation possible at a young age.
Habitat and Geographical Range
Eastern Bluebirds favor open woodland, meadows, pastures, orchards, and areas with scattered trees. These birds are cavity nesters, often relying on tree holes or nest boxes for breeding. They are frequently seen perched on fences or wires, scanning the ground for insects, which form a large part of their diet.
Geographically, The Eastern Bluebird is found throughout much of the eastern United States and parts of Canada. They are a partially migratory species, moving with weather patterns and food availability. Some populations that live in mild zones do not have to travel far in the winter months to find warmth or an abundance of food. They range from the southernmost regions of Canada to as far south as Central America during the winter. Most populations of Eastern Bluebirds do not venture west past Texas, Oklahoma, and Kansas. In Mexico, populations are sporadic but tend to be state-wide and not limited to the east or west coasts of the country.
Common Misidentifications
Eastern Bluebirds can sometimes be mistaken for similar-looking blue songbirds, such as the Western Bluebird, Sialia mexicana, and the Mountain Bluebird, Sialia currucoides. The Western Bluebird is more prominent in the western United States (Arizona, California, Nevada, Oregon, Idaho, Montana, and Washington State) and has a more uniform blue on its head and back. The Mountain Bluebird lacks the reddish-orange breast entirely and is mostly sky blue. The vivid chestnut or rusty color of the Eastern Bluebird’s breast is a key distinguishing feature.
Conservation Status
From a conservation perspective, the Eastern Bluebird is currently considered to be of Least Concern and has a stable population. This species wasn’t always as fortunate and has made a remarkable recovery thanks to dedicated conservation efforts. After a decline due to habitat loss and competition for nesting sites from invasive species like European Starlings and House Sparrows, the introduction of bluebird nest boxes helped boost their numbers.