Eastern bluebirds are considered partial migrators. Depending on the area of residence, individual bluebirds will likely reside in their location year-round. However flocks may migrate for better resources such as mating ability, food, shelter or to escape the cold.
Below is the eastern bluebird range map. As you can see, for a large portion of the United States, these thrushes will usually stay put. However, what you may discover if you host bluebirds is an increased population come winter time. This is especially the case if you have a yard set up with fatty foods, berries, mealworms and water (unfrozen).
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Why do some eastern bluebirds migrate?
Some bluebirds breeding and nesting in the northern regions of their range will migrate into southeastern areas of the United States, or even as far south as Mexico.
The key reason determining why some bluebird populations will migrate has to do with resources and environment. For instance, migrating northward for breeding will have to do with territory, competition, availability of a mate and food.
An older study taking place in Michigan followed nearly 300 bluebirds observing nesting and breeding behavior. Of the 300, there were 61 with known histories that could be better studied. Of the 61 known bluebirds, only 18 remained in the study area year-round, while the other 43 had migrated into the study area for the breeding season (Pinkowski, 1977).
The northern migration has enabled bluebirds to expand their species into other areas of North America.
Come winter time, resources will again influence bluebird population migration. Food and territory are one factor. But certainly the weather is going to be another reason bluebirds may decide to move southward.
Migrating populations of the far northern parts of the US and into Canada will travel a much greater distance. Whereas populations in the midwest, may migrate very minimally.
When do eastern bluebirds begin to migrate?
You might think migratory bluebirds breeding in the north will begin their southward travel as the weather gets cooler. However, this is not quite the case.
Researchers found bluebird migration is greatly influenced by photoperiod, or how many hours of sunshine there is in a day. Therefore, as the days grow shorter and there is less exposure to sunlight, migratory bluebirds are prompted to travel south.
That’s not to say weather and temperature don’t have any influence on migrating bluebirds. Populations traveling a longer distance may stay in foraging areas longer if the weather is mild, and move on as the weather gets colder or less hospitable (Richardson, 2000).
It has been hard for researchers to fully determine when breeding migration occurs. This is attributed to the challenge of differentiating resident bluebirds from migratory bluebirds. Some data is known, however.
Table of known eastern bluebird migratory periods to breeding grounds in select locations
| Arriving to | Beginning of breeding migration | Peak migration period |
| Cape May, NJ | Not provided | March |
| Massacheusettes | Not Provided | Late February – March |
| Michigan | March | Late March – Late April |
| Minnesota | Early March | Early April |
| Missouri | Late February | Mid March – Early April |
| Ohio | Late February | Early March – Early April |
| Quebec | Not Provided | Mid March – Early April |
While eastern bluebirds breed in a large range within North America, the above table is data gathered from Rick Toochin and Don Cecile’s paper “The First Record of Eastern Bluebird (Sialis sialis) in British Columbia” (2018), and Benedict Pinkowski’s paper “Foraging Behavior of the Eastern Bluebird” (1976).
Another theorized factor that might influence when bluebirds migrate has to do with food availability, particularly when it comes to insects. Rather than migration being solely determined by seasonal photoperiod, some researchers are considering insect alignment to be an important driver of migration.
One of the reasons for this theory has to do with migration and nesting shifts over the years. And climate change is suspected to be a reason for these shifts, but not in the way you might think.
As we established, temperature is not necessarily the biggest driver in big-picture migration. Therefore a shift in climate and changing temperatures isn’t what is believed to have caused nesting and migration shifts.
Instead, researchers are considering the impact climate change has had on the emergence of seasonal insects. Shifts in their emergence, which therefore impacts their availability or limitations, may be factored into when bluebirds and other insectivores migrate (Sockman, & Courter, 2018).
How far do migrating bluebirds travel?
There is record of eastern bluebirds breeding in Manitoba, Canada and wintering in central Texas. This would be a travel distance of 2100 Kilometers or 1304 miles. However, the distance migrating eastern bluebirds travel really depends on individuals and populations.
In terms of migrating behavior, it is believed that migrating eastern bluebirds perform “leapfrog migration.”
To understand the concept of leapfrog migration, imagine jumping over someone, just like playing “leapfrog.” In this case, northerly birds traveling south will not migrate down in a gradient, roosting or taking up vacated sites of other migrating bluebirds. Instead, they will migrate past other resident birds – or over resident birds in a leapfrog type manner.
Therefore, while bluebirds are considered to be “short-distance migrators,” which is true when comparing them to tree swallows, some eastern bluebird populations will migrate a fairly long distance to get to warmer territory or return back to their northern breeding grounds.
Dangers for eastern bluebirds during migration
Bluebird migration presents several risks including predation, environmental fatalities, and traveling injuries.
Travel always creates risk. Though bluebirds will have a fairly general route, traveling almost due south or due north, and will return to the same areas year after year, there is still a lot of uncertainty along the way.
A more recent issue that can impact traveling bluebirds, whether traveling north into breeding territory or southward has to do with tree loss.
During unexpected, severe cold snaps, hardy trees offer important shelter to wintering and traveling bluebirds. In these situations, traveling flocks will roost together in trees or roost boxes put out by trail managers to keep warm.
Body temperature, especially combined within flocks, can significantly minimize heat loss.
Furthermore, if small flocks roost in tree holes or nest boxes during the winter nights, the closed environment can help retain and maintain heat during the coldest part of the day.
Another powerful element of cavity shelters is that bird movement can help provide heat. During restless periods, which birds will experience at night, box temperatures can increase.
Despite being used to the elements, even they fall susceptible. During late 2020 and early 2021, there were several reports of dead birds, including dead eastern bluebirds as a result of lower than normal temperatures.
The cold temperatures had such an impact that bluebird landlords expecting regular pairs along their trails, had several vacant boxes.
Food scarcity along the way can also have disastrous consequences for migrating birds. As we mentioned, there is a theory that bluebird migration is also influenced by food abundance or limitations. If unexpected weather impacts food supply, causing shortages, traveling birds and even residential birds run the risk of weakening and falling prey to other animals.
How to help migrating bluebirds
Based on the fact that bluebirds will migrate south in a leapfrog manner, and travel even as far south as into Mexico and Central America, there are some ways you can help migrating bluebirds.
Quick ways to help migrating bluebirds are to provide berry plants that fruit during the winter, supplement food, provide a heated water bath for hydration, and put up monitored nest boxes for nightly shelters.
Here, we’ll list out each way to help migrating bluebirds in greater detail. Even if you’re not sure if you have bluebirds migrating in your area, these steps can help your resident bluebirds thrive, which is very important.
You may also want to check out our guide and checklist for attracting bluebirds to your yard. There are some things that can make or break a bluebird sanctuary.
Plant berry bushes, especially ones fruiting in the fall and winter
Berry trees and shrubs are especially important to both migrating and residential bluebirds as well as other birds because they provide a nutrient packed food source when the ground is frozen and insects are inaccessible. Furthermore, berry trees and shrubs provide cover and shelter for birds.
The berries on arrowwood plants, for example, are high in fats, which is crucial for wintering birds. When berries are ripe, expect to see bluebirds, mockingbirds, robins and northern flickers, just to name a few, picking at these berries.
Below is a table of berrying plants along with their fruiting period and hardiness zone.
The concept of hardiness zone can be a little hard to understand. Essentially, it has to do with how hardy a plant is when it comes to enduring the cold. The lower the zone number, the colder the region. The zone regions are provided on the table along with a zone map.
If you’re considering choosing some of these plants to add to your yard, consider offering seasonal varieties with the most abundant quantities in the winter time.
For example, plant a combination of blackberry, native honeysuckle and arrowwood, planting more arrowwood for wintering birds. Combinations help cover more of the seasons and also provides some dietary variety.
Keep in mind, some of these plants can quickly get out of control, leading to suckers and yard takeover. When researching which plant types, look for cultivars that are more manageable, or come up with a management plan. It can be as simple as quarterly trimmings.
Berry plants for birds along with fruiting season and hardiness zone
| Berry Plant | Fruiting Period | Zone |
| American Blackberry | Summer | 5-10 |
| American Elder | Summer | 3-9 |
| Black Huckleberry | Summer | 3-7 |
| Black Cherry | Late Summer | 3-9 |
| American Beauty Berry | Late Summer Into Fall | 7-11 |
| Black Currant | Summer and Fall | 4-8 |
| Pokeweed | Summer and Fall | 4-8 |
| Native Honeysuckle | Early Fall | 5-8 |
| Firethorn | Fall | 6-9 |
| Flowering Dogwood | Fall | 5-9 |
| Smooth & Staghorn Sumac | Fall and Winter | 5-11 |
| Northern Bayberry | Fall Into Winter | 4-6 |
| Mountain Ash | Late Fall Into Winter | 2-5 |
| Arrowwood | Late Fall Into Winter | 3-8 |
| Inkberry | Fall and Winter | 5-9 |
| Winterberry | Fall and Winter | 3-9 |
Supplement food for bluebirds during the winter and summer seasons
Supplementing food for both migrating and residential bluebirds can be extremely helpful. One of the best go-to foods for bluebirds is mealworms.
Mealworms for bluebirds
Freeze dried mealworms are cheaper to come by and are still eaten by bluebirds, but they are not as hydrating or nutrient rich as live mealworms.
During the breeding period, especially in the heat of the summer, providing live mealworm is especially important because it becomes a hydration source for nestlings without over-exhausting bluebird parents.
If you happen to know that a very hot day or several hot days are coming up, have ready a good supply to last the week.
A thousand live mealworms can go very quickly, especially after bluebirds have fledged. Not to mention, other birds such as Carolina wrens will be interested in the mealworms.
Do not worry about bluebirds losing their survival edge when you provide food. They will also hunt. The mealworm provision is simply an added benefit during hot periods so that bluebirds aren’t exhausted or overheat. They can also be extremely important during freezing snaps when the ground is frozen and food is hard to come by.
Nutritional concerns when providing bluebirds with mealworms
There is concern when supplementing food, especially with mealworm and that is the limited nutrient availability.
For example, mealworms are not rich in calcium, which is a very critical mineral for female birds during the nesting season. Laying eggs depletes a female bluebird’s calcium supply (and any bird).
When supplementing with mealworm, providing calcium sources such as sterilized pulverized eggshells and a little bit of wood ash can help.
Consequences of calcium deficiency include weak, fragile eggs or egg bound mother birds.
Egg bound is a term for a situation where an egg becomes stuck in the oviduct of a bird.
The bluebird banquet, an important winter snack for migrating bluebirds
The Bluebird Banquet is another winter option. It is composed of peanut butter, cornmeal, unbleached flour, peanut hearts, sunflower seed chips, and soaked raisins.
Two notes of caution when it comes to the Bluebird Banquet: First, some birders have claimed that the salt in peanut butter can be fatal. It is extremely easy to throw off a bird’s electrolyte balance. Therefore, the concern about salt is an important one. We have not been able to confirm this. However, to be safe, we suggest using salt-free peanut butter.
Second, fatty cakes like this and suet can attract other birds, which is not usually a problem unless invasive starlings start to flock.
Starlings, which are invasive and are a huge threat to native cavity birds and will hoard feeders during winter time.
Bluebird Banquet Recipe:
- 1 cup peanut butter
- 4 cups cornmeal
- 1 cup unbleached flour (whole wheat)
- Add the following:
- 1 cup fine sunflower seed chips
- 1 cup peanut hearts or finely ground nuts
- 1 cup soaked raisins cut in halves or currants (preferred)
- Stir in rendered melted suet (you can get suet from a butcher or meat market) Bacon grease is not recommended.
Let the entire mixture cool. When you set it out, it will have a broken up consistency. If the mixture is too gooey or liquidy, you can thicken it up by adding more flour.
Providing a heated water bath critically serves migrating bluebirds
Water is essential for survival, but during the long freeze of winter, available water is very hard to find.
Either providing a water bath heater or a heated water bath offers an incredible sanctuary to migrating and resident bluebirds as well as other birds in the area.
Water bath heaters are not very expensive. They can be plugged into an outdoor extension cord. One helpful tool is a waterproof cover that goes around the plugs to protect them from the elements.
Providing monitored nest boxes for roosting gives bluebirds an important winter shelter
If you’ve provided plenty of food and water for bluebirds, one of the last steps to help them out is to put your nest box up if you have one, or consider purchasing one.
Many bluebirders will also include pine needles in the boxes for soft bedding and greater insulation.
During extremely cold weather, nest boxes are a way for bluebirds and other cavity birds to roost and maintain body heat. Often, small flocks will roost together, which will help keep the inner temperature warmer than the outside environment.
One concern with winter roosting is suffocation. This can happen when too many birds are roosting in one box and there is not enough air flow (note, that some birders advise plugging up ventilation holes in order to minimize heat loss). Putting up multiple boxes may help remedy this situation. However, if you do discover tragedy, remember that you did all you could. Nature can be brutal at times.
Takeaways:
- Only some populations of bluebirds migrate.
- By comparison to other birds, bluebirds are short distance migrators, with some traveling as far as 1300 miles.
- Bluebirds breeding in the northernmost range will migrate south in a leapfrog like manner.
- When bluebirds migrate is believed to be determined by the increase or decreasing daily sunlight.
- Some researchers have hypothesized that bluebird migration may be more influenced by food availability.
- Ways to help migrating bluebirds and residential bluebirds especially at winter time is to provide a variety of fatty foods, access to water (not ice), and providing places for bluebirds to roost.
References
CHARLES, S. (N.D.). Energy of Birds Conserved by Roosting in Cavities.
Cornell Lab. (n.d.). Eastern Bluebird Range Map, All About Birds, Cornell Lab of Ornithology. All About Birds, Cornell Lab of Ornithology. https://www.allaboutbirds.org/guide/Eastern_Bluebird/maps-range.
Ellis, M. E. (2019, November 5). USDA Zone Explanation – What Do Hardiness Zones Mean Exactly. Gardening Know How. https://www.gardeningknowhow.com/planting-zones/what-do-hardiness-zones-mean.htm.
Meyer, K. (n.d.). Zoning in on Hardiness. Proven Winners. https://www.provenwinners.com/learn/zoning-hardiness.
Pinkowski, B. C. (1977). Breeding adaptations in the Eastern Bluebird. The Condor, 79(3), 289-302.
Ritchison, G. (2000). Eastern Bluebird. Stackpole Books.
Toochin, R., & Cecile, D. The First Record of Eastern Bluebird (Sialia sialis) in British Columbia.
Woolwine House Bluebird Trail. (2014, February 25). BLUEBIRD BANQUET (Suet Recipe) – WINTER 2014. This is the WOOLWINE HOUSE BLUEBIRD TRAIL. https://woolwinehousebluebirdtrail.com/2014/01/15/bluebird-banquet-suet-recipe-winter-2014/.
