The three species of bluebirds found across North America—the Eastern, Western, and Mountain Bluebird—are admired for their vibrant plumage. Their survival depends on a diverse diet that shifts dramatically with the seasons and geographical location. These thrushes are categorized as omnivores, consuming a mix of animal and plant matter, which allows them to thrive in various habitats.
The Primary Diet: Insects and Arthropods
During the warm spring and summer months, the bluebird’s diet is heavily focused on animal protein. Invertebrates make up approximately 68% of the adult diet and an even higher percentage for young birds. The majority of this protein comes from ground-dwelling prey like grasshoppers, crickets, beetles, and moth or butterfly larvae, such as caterpillars.
Bluebirds are masters of a foraging technique called ground-sallying or drop foraging, which relies on keen eyesight and open terrain. The bird perches on a low branch, fence post, or wire, scanning the ground for movement. Once a target is located, the bird swoops down quickly to capture the insect, returning to a perch to consume the meal or prepare it for its young. The Western and Eastern Bluebirds primarily use this method, while the Mountain Bluebird employs a unique hovering technique over open fields to spot its prey.
Spiders, earthworms, and various other arthropods like sowbugs are also regularly consumed to meet the intense metabolic demands of raising multiple broods. The efficiency of their hunting methods allows them to consume a significant volume of insects daily, which also makes them effective natural pest control in open areas.
Seasonal Foraging: Fruits and Berries
As temperatures drop in the late fall and winter, the availability of insects and other arthropods declines, forcing a significant shift in the bluebird’s food sources. Their winter diet transitions to fruits and berries, which, while less protein-dense, provide the necessary carbohydrates and fats for energy and survival in the cold. This change is driven by scarcity, as the birds are no longer focused on the protein requirements of nesting.
Bluebirds seek out native plants whose fruits persist on the branch long into the cold season, offering a reliable food source. Preferred native selections include fruits that remain viable even after freezing:
- Sumac
- Flowering dogwood
- Holly
- Virginia creeper
- Red cedar
- Wild grape
These fruits and berries are also an important source of hydration during the winter, especially when natural water sources are frozen. The ability of bluebirds to switch to this frugivorous diet is what allows many populations to remain in northern latitudes rather than migrating south.
Human Provided Supplemental Foods
Offering supplemental food can support bluebirds, particularly during inclement weather or the demanding nesting season. Live mealworms are the most successful offering, as they mimic natural insect prey and are rich in protein. These can be offered in a smooth-sided dish or specialized feeder.
Freeze-dried mealworms are also accepted, but they should be rehydrated with water or mixed with a suet dough. They are not suitable for nestlings because they lack the moisture of live insects. Suet is another excellent energy source, especially suet mixes formulated for insect-eating birds, often containing rendered animal fat blended with peanut butter or cornmeal.
Avoid offering foods that are unnatural or potentially harmful to bluebirds, such as kitchen scraps, bread, or large seeds. Salted nuts should also be avoided, as excess sodium is detrimental to their health, making unsalted, chopped nuts the only appropriate choice.