While it’s tempting to think of Bald eagles (Haliaeetus leucocephalus) as occupying only mountain regions, Bald eagle populations stretch from the far east to the far west of North and Central America. They can be found as far north as Alaska and northern Canada and as far south as Chihuahua in Mexico. Many species of eagles are non-migratory, but what about Bald eagles? And do Bald eagles migrate?
Many Bald eagles do migrate across the USA, Canada, and some of Central America - they are described as partially migratory. Once a Bald eagle finds a mate and establishes a territory, it needs a good reason to leave, such as food scarcity. Bald eagles distributed in Alaska and the Pacific Northwest usually migrate at the end of summer most years. Those distributed further south and on the southwest US coast rarely migrate.
Bald eagle migration is complex and is highly sensitive to environmental conditions. The primary motivation for migration is food scarcity, especially in winter when the lakes begin to freeze and animals retreat into their nests and burrows for hibernation.
When food is scarce, Bald eagles tend to roam southwards, but some actually head north instead. If you’re very lucky, you might see a flock of 10 to 20 Bald eagles migrating in the same direction - this is one of the only times that they’re sociable.
Read on to learn more about the fascinating migratory behaviours of this magnificent eagle.
Many Bald Eagles do migrate
Bald eagles in the far north tend to head south anytime from the end of August to as late as January. The reasons why some migrate so late in winter is still poorly understood, but migration is nearly always linked to food scarcity.
Bald eagles in the Great Lakes region often head south in winter, following rivers and waterways through the Appalachian Mountains. Eagles from the Northwest Territories, Alberta and Saskatchewan migrate south earlier than other populations in around September.
On the Pacific Northwest coast, Bald eagles often head north in winter, likely to track salmon as they head north. Eagles as far south as California can head all the way to Alaska in search of salmon.
This seems to present a conundrum - why would some eagles head north and some south? It may be that different eagles have different food preferences, or that some are particularly keen to travel the movements of autumn/winter salmon.
The migratory behaviours of juvenile Bald eagles are slightly different; they are more likely to wander in any direction and don’t necessarily follow a typical north to south or south to north migration route.
The abundance of Salmon is a key factor for Bald eagle migration
Bald eagles migrate almost solely to find food. This is why they head both north and south, and out to the coast and inland.
In North America, winter doesn’t always correlate with decreased food abundance as some aquatic animals head north to spawn in colder waters. Bald eagles are not the only American bird to head north in winter - pelicans are another notable example.
Salmon is a key motivator for Bald eagle migration - salmon are complex and interesting migrators themselves! When salmon return upstream to their spawning grounds, eagles may follow them. When rivers and lakes freeze in their northern territories, Bald eagles likely head south until they find fresh, unfrozen water again.
It’s worth mentioning that Bald eagles are actually a species of sea eagle, and some populations consume almost solely fish. The average Bald eagle’s diet consists of 50%+ fish. This is why locating fish-abundant water is a maximum priority in winter when lakes begin to freeze over.
Close up portrait of a Bald Eagle (Haliaeetus leucocephalus)
Bald eagles tend to migrate by day and seek out thermal currents and winds to carry them in the direction they need to go. Radio-tagged migrants have been recorded travelling over 200km in one day with an average speed of 30km/h or so.
Rather than expending energy by flapping their wings, Bald eagles choose to soar at a height of around 1,500 to 3,050 m.
Certainly not - it's unclear how many Bald eagles migrate. Populations distributed further north seem most likely to migrate, unless they can compensate for their loss of food by tracking winter salmon populations.
Even then, some populations in the upper reaches of Alaska remain there all year round, whereas others choose to migrate. The reasons why there is no consensus depend on available food.
Three bald eagles perched in the Alaskan Kenai mountains
The further south you go, the less likely it is for Bald eagles to migrate. Those distributed further south than California, Wyoming, Nebraska, Missouri and North and South Carolina are generally sedentary and don't tend to roam too far from their territories. However, there are exceptions - Bald eagles in Florida often migrate north up the Atlantic coast, across the Appalachian Mountains, and through the Mississippi River valley.
What does seem clear is that all migratory eagles return to the same breeding grounds each year. Bald eagles are territorial creatures and tend to fly great distances out of necessity rather than desire. It may be that different eagles have different strategies for locating food during winter, or that they choose to migrate for reasons we simply don't understand.
Juvenile Bald eagles tend to roam rather than migrate. After they fledge the nest and leave their parents, juvenile Bald eagles can spend 3 to 4 years exploring. By the end of their great exploration, they’ll be approaching sexual maturity and will look to establish a territory with a mate.
Juvenile Bald Eagles perched on the water
Bald eagles are more likely to travel north along the warmer Pacific Northwest coast. Whilst some eagles travel south from Alaska, British Columbia, the Northwest Territories and Alberta, others head north along the coast in search of salmon.
In the west, Bald eagles rarely, if ever, travel north during the winter. Instead, they tend to follow rivers and waterways inland.
Bald eagles do not migrate for the sake of warmth alone, and some stay in the upper reaches of Alaska all year round, where temperatures can plummet to -35C.
Bald eagles have an incredibly thick, dense coat of thousands of feathers that are great at trapping heat. They can also induce a state of active hypothermia, which allows them to control their energy expenditure, using up just as much energy as they need to stay warm without wasting any. By scaling back their foraging behaviours, Bald eagles channel more energy into staying warm.
Winter is one of the only times that Bald eagles join up in communal groups - non-breeding Bald eagles often form roosting flocks, huddling to stay warm on freezing nights.
Bald eagle stood on a snowy hill during the winter
Bald eagles usually migrate alone or in their mated pairs, but do rarely join each other in flight.
Columns of mitigating Bald eagles have been spotted flying together, especially along major rivers such as the Mississippi. Juveniles are most likely to form small flocks during migration and tend to stay away from adult birds.
Bald eagles in Florida tend to remain there all year round. However, some migrate to Florida, or at least may wander over its western edge. Those migrating from Florida head up the Atlantic coast or across the Appalachian Mountains or Mississippi River valley.
Bald eagles migrate to Canada from the Arctic and also migrate from Canada south to the USA and western and eastern coasts. Bald eagle migration in Canada is complex, but those distributed in its northerly-most regions are likely to migrate once their lake fishing grounds freeze over. They may only travel as far as they need to go to find freshwater fish, like salmon.
Around 1,000 Bald eagles migrate to or over Colorado each year. Birds from Canada or Alaska can be found foraging and fishing in Colorado’s rivers and lakes in around September to December.
Resident Bald eagles in Colorado may stay all year round, providing they can find food during the winter.
Bald eagle taking flight
Bald eagles can be found in most of Michigan’s counties, and most populations seem to remain residents, choosing not to migrate.
Minnesota’s Upper Mississippi River is a major migration route for Bald eagles heading south in the winter. Bald eagles head along the Mississippi from Wisconsin and Canada. Many Bald eagles are attracted to the Mississippi Valley due to its abundance of fish.
Resident Bald eagles in Washington State tend to inhabit the Puget Sound region. The Pacific Northwestern coast is a key migratory route for Bald eagles heading both north and south. Washington State’s resident Bald eagle populations often increase in winter.
Many Bald eagles migrate from Canada and the Great Lakes region to Maine, and some will stop in Vermont. As a result, Vermont is home to both migratory and resident populations of Bald eagles.
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