Migratory birds that live in temperate regions tend to migrate south in search of warmth, food and a place to breed. A common sense rule which, however, apparently does not apply to all birds: a study published in Journal of Raptor Research tells of a population of bald eagles from Arizona that migrates north every year, reaching as far as Canada. It seems like a paradox, but it makes sense.
There are those who stay and there are those who go. Bald eagles, also known as bald eagles, are one of the best-known symbols of the United States. Spread throughout North America, they are “irregular” migrants: when they are in a place that has access to water (and therefore food) all year round they tend to stay there, while if they live in an area where the water freezes in winter, they migrate in search of new food sources. The case of the Arizona population that was studied is instead mixed: some specimens migrate, others remain close to their nesting places throughout the year.
A question of reproduction. The difference lies in age and reproductive status. In fact, those who migrate are the young, who are not yet old enough to reproduce, and those adults who that year were unable to find a female and set up a nest.
These specimens are the most difficult to study: bald eagles are usually observed directly, and young (and single adults) who wander away from the nest risk being lost from sight.
The research. That’s why the University of Arizona team decided to “tag” 24 juveniles and two non-breeding adults, and follow their movements between 2017 and 2023. By observing them in this way, the researchers discovered that these eagles do not migrate south in search of warmer climates, but north. This is because, for bald eagles, the nesting season is winter, while summer and autumn are more “free”. Young specimens use these periods to explore and look for seasonal food sources, for example salmon.
To the north, hunting for food. Observation over the years has also shown that eagles improve their navigation skills season after season, but also that their journey north, which as mentioned takes them to the borders of Canada, is quite dangerous: the study tells the story of an eagle which, after crossing ten states and four Canadian provinces, settled in California, only to then die due to an excessively strong electric shock.
This is why it is important to know the migratory paths of bald eagles: it is a way to protect them.
