Bluebirds are small, colorful songbirds found throughout much of North America. While many birds migrate south for the winter, some bluebirds have adapted to survive the cold northern winters. Bluebirds have developed specialized adaptations and behaviors that allow them to make it through the tough winter months.
Why do some bluebirds stay in the north for winter?
Not all bluebirds migrate south for the winter. Eastern Bluebirds and Mountain Bluebirds especially can be found year-round across much of the northern parts of their range. There are a few key reasons why some bluebirds stick it out through the winter rather than migrating:
- Availability of food – Some bluebirds have learned to switch their diet to fruits and seeds that are available even in winter.
- Nest cavities – Bluebirds rely on tree cavities for nesting and roosting. Staying in one area year-round allows them to reuse and defend nest sites.
- Milder climate – Western and Mountain Bluebirds that winter in the southwest and western U.S. experience relatively mild winters compared to the far north.
- Competition – Migration carries risks and challenges. Remaining in one territory can help bluebirds get a head start on competition in the spring.
So while migration is a good strategy for many birds, some bluebirds find they can survive just fine staying put for the winter. Their adaptations allow them to tough it out.
How do bluebirds find food in winter?
Finding enough food is one of the main challenges bluebirds face when staying north for winter. With insects scarce, they must switch their diet to focus more on fruits, seeds, and small rodents.
Fruits
Fruit can make up a large part of bluebirds’ diet in fall and winter. They eat fruits whole, concentrating on small, softer fruits like sumac, juniper, hackberry, and dogwood. Bluebirds will also visit gardens and backyards to eat raisins, currants, cherries, and other small fruits put out on platforms and in suet feeders.
Seeds
Seeds from grasses, flowers, weeds, and other plants provide essential nutrition. Bluebirds sweep their beak along the ground to scoop up fallen seeds. They also glean seeds from flower heads and seek out brush piles with concentrations of seeds.
Suet
Suet feeders are excellent sources of food for wintering bluebirds. Suet provides fat and protein from rendered beef fat or seed-based cakes. Bluebirds cling to suet feeders and nibble away small bits.
Small prey
While not their main food source, bluebirds will eat small rodents like mice and voles when other food gets scarce. They can hunt by scanning the ground from a perch before swooping down on prey. This helps supplement their diet with protein.
How do bluebirds keep warm?
In addition to finding food, bluebirds have physical and behavioral adaptations to survive freezing temperatures and snowy conditions:
- Insulative plumage – Bluebirds fluff out their feathers to trap a layer of air against their skin for insulation.
- Shivering – They shiver to raise their body temperature and can raise their metabolism by over 50% in winter.
- Roosting in cavities – Tree cavities act as high-insulation shelter to get out of the wind and cold.
- Caching food – Bluebirds hide food in winter to create emergency stashes when other sources are covered in snow.
- Fluffing feathers – Fluffing out their plumage creates air pockets for insulation.
- Fasting – Bluebirds can drop their metabolism and body temperature by several degrees overnight to conserve energy.
- Sunny exposures – They choose roosts with sunny exposure to gain solar heat.
These adaptations allow bluebirds tomaintain a healthy body temperature and energy level even in harsh conditions.
How do bluebirds avoid predators?
Bluebirds face threats from predators trying to take advantage of scarce winter resources. Predators include sharp-shinned hawks, Cooper’s hawks, merlins, weasels, squirrels, and eastern chipmunks. To avoid predation, bluebirds use several strategies:
- Roosting in dense thickets and cavities
- Mobbing predators with alarm calls
- Rapid takeoff when threatened
- Traveling in flocks for safety in numbers
- Watching vigilantly for danger
- Diving and swooping to drive off predators
- Nesting in tree cavities out of reach
Staying alert, vocalizing threats, hiding, and aggressively defending against predators are key behaviors bluebirds use to lower their predation risk.
How do bluebirds attract mates and breed in winter?
Breeding during winter brings huge benefits but also challenges. Bluebirds attract mates with vocalizations and displays. They may start pair bonds as early as December. To successfully breed in winter, they:
- Choose sheltered nest sites in tree cavities to protect from cold.
- Insulate the nest with fine grasses, pine needles, fur, feathers.
- Wait until snowmelt to find food and build energy for egg laying.
- Heat eggs and chicks through brooding and sheltering.
- Have males bring food to incubating females so they don’t have to leave the nest.
- Have helpers at the nest such as older siblings.
- Nest in loose colonies to provide protection.
Winter breeding improves their chances of having multiple broods and lowers competition in spring. It’s a risky strategy but pays off if they can successfully incubate eggs and rear chicks through the worst cold.
How do bluebirds interact at winter roosts?
Bluebirds form communal winter roosts, congregating in dense thickets,rees groves, and cavities to share body heat. Roosts can include:
- 3 to 4 birds for smaller roosts
- 10 to 20 birds for medium roosts
- 50 to 100+ birds for large roosts
At the roost, bluebirds:
- Arrive near sunset and gather close on branches.
- Chatter and twitter before settling in tightly.
- Fluff feathers to trap insulating air.
- Huddle together, shoulder to shoulder.
- Take turns on the inside and outside of the huddle.
- Shuffle positions at night to share warmth.
- Leave together at dawn.
Shared body heat in the roost allows them to withstand frigid nights.
Conclusion
Bluebirds are resourceful, tough birds capable of surviving even brutal winters. With adaptations like specialized winter diets, cavity roosting, winter breeding, and communal roosting, certain bluebird species are able to live year-round through harsh northern winters. Their flexibility and resilience reminds us to never underestimate the challenges wildlife can overcome with the right adaptations and behaviors. Bluebirds show that with ingenuity and determination, it’s possible not just to survive but thrive in even daunting conditions.
