Welcome to “Stuff Your Neighbor Knows,” a column where we ask questions about the natural world and a community member with a relevant background provides an answer.
Our first question is: “Do our bald eagles migrate?”
To help answer is Roaring Fork Valley resident Mark Fuller. He has been an avid birdwatcher in the Valley for 53 years and involved with the Roaring Fork Audubon Society in some capacity for over 12. He is the photographer for the local guidebook, “Birds of Aspen and the Roaring Fork Valley.”
Fuller’s voice brightens and his words quicken when I ask him about eagles. He has been watching them along our rivers since his first sighting in the ‘70s. “I can remember when seeing a bald eagle in the Valley would make your hair stand on end,” he shared.
Fuller estimates we have around 20 bald eagles during the winter — the most throughout the year, in fact. About two-thirds of these bald eagles will remain year-round. The other third flies away to their summer home as the weather warms. He and others in the Valley generated these estimates from summer nest observations and winter bird counts over the past several years. He mentioned a bald eagle census would be a good project for the Roaring Fork Audubon to spearhead in the coming years — sign me up!
Why do we have more bald eagles in the winter than the summer? I imagine a flock of eagles flying in a group down from Alaska, resting here during the winter to enjoy the great fishing and then heading north when the weather warms, back to their salmon. I mentioned this image to Fuller. Is this a romantic notion? Yes. Realistic? No.
Fuller takes a beat, “Well, bald eagles don’t migrate like songbirds do.”
With these eagles, we aren’t talking about the journey of the monarch butterfly or the broad-tailed hummingbirds (stories for another time). Bald eagles, to use Fuller’s term, “disperse.”
Bald eagles travel from an area where their food source (rivers, lakes, reservoirs and oceans) freezes to an area where it’s not completely so, and fishing is still practical. The dispersed birds are faithful to their summer and winter homes. They return to the same places year after year. While we might be seeing new-to-us birds in the winter, they are often the same birds for consecutive years.
Why would these eagles ever leave if the winters are good, and the Roaring Fork Valley has habitat that can support them year-round? Well, our habitat can only support so many permanent resident bald eagles. In addition, adult, breeding bald eagles are “very territorial,” Fuller explained, “and they have a big territory.”
Nesting season begins around March. During this time, nesting pairs will aggressively protect their nest, food source and established territory.
Compared to our year-round residents, the winter visitors are often younger, non-breeding and skew male. Adult, breeding-age female bald eagles are larger than the younger male winterers and can chase them out of a territory. While Fuller has never seen an eagle battle, a quick YouTube search generates many videos of bald eagles injured from talons bared in territory disputes. (Territory disputes are not to be confused with the mating air-dance bald eagles execute where they lock talons and spiral in a freefall, which is also a fantastic YouTube search; and with mating season being in early spring, keep your eyes to the skies.)
Thanks for reading and please email stuffyourneighborknows@gmail.com if you have a question about the Valley’s environment or natural world — I’m sure your neighbor has an answer!