8/29/16 – Migration in Bald eagles

Migrating waterfowl 8/23/16 Charlo, MT. Image courtesy of Explore and Owl Research Institute
Migrating waterfowl 8/23/16 Charlo, MT. Image courtesy of Explore and Owl Research Institute

8/29/16 – Migrating in birds is all about flying south for the winter, right? Those classic V-formations of honking geese heading south as a harbinger of winter is deeply ingrained in American culture. Well, as with many things in life, migrations can be more complicated than that.

Bald eagles are found across much of North America and they face many different types of environments and challenges. Bald eagles exhibit a wide variety of behaviors when it comes to migration.

Those hatched in the southern areas have enough time to migrate north during the latter part of the summer, before turning around and heading south for the winter, back to where they started. Eagles that live farther north only have enough time in their season to head south in the fall and return to the north in the spring.

But do all Bald eagles migrate? No, it is not that simple either!

In areas that ice covers during the winter eagles do move to ice-free areas, but these can sometimes be found nearby in areas with turbulent waters. In Nova Scotia and Maine eagles may remain for the winter, possibly instigated when wildlife officials offered pesticide-free carrion for eagles to feed on during the post-DDT recovery era.

Eagle warning sign courtesy Hal Heatwole
Eagle warning sign courtesy Hal Heatwole

In the Aleutian Islands and Chilkat River in Southeastern Alaska eagles may find enough food to remain for the winter, or move locally among the rivers of the Pacific Northwest to exploit various salmon runs. While eagles hatched much farther south, from California to Arizona, and north to the Greater Yellowstone Ecosystem also move into the area to feed on spawning salmon.

Eagle and bridge over Iliuk River courtesy of Hal Heatwole
Eagle and bridge over Iliuk River courtesy of Hal Heatwole

So Bald eagles migrate to feed on salmon? Yes, but it is not that simple either. Farther east, from heart of the Great Plains to the western front of the great eastern Boreal forests Bald eagles funnel into the waters of the Upper  Mississippi River to feed on Gizzard Shad during the winter. In other locations the creation of reservoirs and dams and the introduction of fish has drawn eagles to feed during the winter. They also feed on other food types as well, exploiting waterfowl or jackrabbits in some locations.

Here in Pittsburgh the adult eagles are residents, meaning they are not migrating to new feeding grounds like eagles from areas with harsher winter conditions. Although, trail reporters and nestwatchers of the neighboring Hays pair do report an absence of eagles for a short period in the fall which may correspond with them exploiting a more abundant food source, we can’t say it is definitely a migration.

Eagle pair in Unalaska courtesy Hal Heatwole
Eagle pair in Unalaska courtesy Hal Heatwole

However, when eagles do migrate they often use traditional flyways, like other birds. This allows eagles to soar on thermals that rise along the coasts, the major rivers and mountain ranges. One of these traditional flyways runs along the Appalachian Mountains, at Kittatinny Ridge. Because these are traditional flyways used by a number of raptor species, you have fantastic viewing opportunities, and researchers have opportunities to track movements and numbers of migrating birds. If you are interested in watching the migrations or participating in their research, please check out Hawk Mountain Sanctuary, located about an hour from Harrisburg or 5-6 hours from Pittsburgh.

Where do eagles from the eastern US go? The Center for Conservation Biology is studying just that question.

For a migration study in the mid-west, see the American Eagle Foundation migration study.

To learn about the migration of eagles in the western US, try Sutton Avian Research Center.

Read more about how and why some Bald eagles (and Peregrine falcons) migrate, and for more in-depth information about avian migration in general, check out this page from Cornell.

 

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