Eastern Bluebird
| Scientific Name | Sialia sialis |
| Survival Strategy | Medium-distance migrants |
| Return to the Midwest | Early March to mid-May |
| Departure | September to November |
| Destination | Southeastern United States and Mexico |
| Conservation status | Least Concern |
Spring
When bluebirds return between early March and mid-May, they immediately explore potential nesting sites. Their arrival is typically a few weeks before tree swallows return to lay claim the same sites, which can trigger some impressive territorial battles. Bluebirds start their first broods in April.
Summer
Bluebirds will raise a second or third brood if the weather cooperates in the early summer.
Fall
Bluebirds leave for their winter range from September through November.
Winter
Eastern bluebirds spend their winter in the southeastern United States and Mexico. Even in the southern parts of their winter range, they can be susceptible to brutal winter weather conditions, reducing the number of birds migrating north to breed in the spring.
Behavior
Flocks
Bluebirds often travel in flocks after the breeding season (late summer through winter). Forming a flock improves the efficiency of locating food and avoiding predators. When migrating bluebirds join resident groups, they learn the location of prime foraging sites. Like any tourist guidebook will tell you, find out where the locals eat to get the best meals.
Communal Roosting
During cold weather, bluebirds will participate in communal roosting. Up to twenty birds will huddle in tree cavities or other tight spaces to share body heat. Anyone who has raised baby chickens has seen this behavior.
Physiology
Shivering
Bluebirds may begin shivering to create extra warmth in cold weather. Unlike humans, birds do not shake when they shiver; instead, they rapidly contract opposing muscle groups.
Waterproof Down Jacket
Bluebirds use oil from their uropygial gland near the base of their tail to keep their contour feathers dry. By fluffing their contour feathers (piloerection), the birds trap air that increases the insulation value of the down layer and reduces the number of calories needed to survive the cold.
Torpor
During cold nights bluebirds may enter a state of torpor to conserve energy. They will drop their body temperature by 10-15 degrees and slow down their metabolism (sometimes called nocturnal hypothermia). Saving energy through torpor is similar to when people turn down their home thermostat to reduce their heating bill.
Diet
Eastern bluebirds are omnivores, and their diet consists of insects, wild fruit, and berries.
Bluebirds forage primarily for insects and other protein-rich arthropods during the breeding season to feed their growing hatchlings. In the cooler temperatures of the non-breeding season, insects become scarce, and bluebirds forage on fruit, berries, and seeds.
Lifespan and Mortality
Eastern bluebirds typically live for 6 to 10 years.
Mortality
Only 30% of the hatch-year bluebirds survive the first year, and most mortality (40%) occurs within the first few months after hatching. Bluebirds that make it to adulthood have an 80% annual survival rate.
Causes of mortality include predation, starvation, and weather-related hypothermia.
Predators
Most predation occurs in or near the nest cavity. Any predator that can reach into or destroy a bluebird box will feed on nestlings. Nest predators include eastern chipmunks, grey squirrels, house sparrows, European starlings, black bears, and raccoons. Domestic cats feed on fledglings with undeveloped flight skills, and American kestrels will prey on adult bluebirds.
Climate Vulnerability
As the climate warms, the range of the eastern bluebird is slowly shifting northward, and nesting pairs are laying eggs sooner. Although this may sound like a win for bluebirds, it has profound implications. Extreme weather fluctuations are more common in early spring, and a Midwest blizzard can leave the bluebird’s food supply covered in deep snow.
Researchers found that drought conditions did not affect the number of eggs laid; however, the hatching rate and the number of birds that fledged decreased.
Never stop learning
First Nations: The Ojibwe word for bluebird is “ozhaawashko-bineshiinh.”
Paleontology: Bluebird fossils dating to 25,000–12,500 B.P. were found in New Mexico.
Citizen Science: The Bluebird Restoration Association of Wisconsin (BRAW) monitors over 7,000 nest boxes and documents about 20,000 bluebirds fledging each year.
References
| Bluebird Restoration Association of Wisconsin www.braw.org |
| Gowaty, P. A. and J. H. Plissner (2020). Eastern Bluebird (Sialia sialis), version 1.0. In Birds of the World (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://birdsoftheworld.org/bow/species/easblu/cur/introduction |
| The Decline and Recovery of the Eastern Bluebird (with Pat Ready) https://youtu.be/LVRfyqf5T5Q |
| The EASTERN BLUEBIRD | A Bird once almost GONE FOREVER! (video) https://youtu.be/xOYZeN6mbTM |
| Weinkam, Todd J., “Winter Behavior and Ecology of Eastern Bluebirds (Sialia sialis): Home Ranges, Habitat Use, and Effect of Weather on Foraging Behavior” (2013). Online Theses and Dissertations. 144. https://encompass.eku.edu/etd/144 |
| Ojibwe People’s Dictionary: Hummingbird https://ojibwe.lib.umn.edu/main-entry/ozhaawashko-bineshiinh-na |