They are born to fly. But even golden eagles only become true rulers of the skies through experience: over the course of their lives, they learn better and better how to use updrafts for their long-distance reconnaissance flights in the Alps, according to transmitter data from 55 specimens. By optimizing energy-saving gliding, the young golden eagles were able to expand their habitat enormously within three years. In addition to their biological significance, the study results could benefit the protection of the prominent birds of prey, say the researchers.
They are famous for their majestic appearance and adorn many coats of arms. However, the admiration has not protected the golden eagles (Aquila chrysaetos) from persecution: in Europe, the large birds of prey were long viewed as a threat and hunted. However, conservation efforts have now led to a welcome recovery in some golden eagle populations – including in the Alpine region. This has also brought the birds back into contact with humans. Research into their behavior is therefore becoming increasingly important.
On the trail of young eagles
So far, comparatively little is known about the young eagles and the development of their behavior over the course of their first years. In order to gain insights into this phase of life, an international research team equipped 55 young golden eagles from nests in Switzerland, Italy, Germany, Slovenia and Austria with small data transmitters on their backs. Thanks to this modern tracking technology, the researchers were able to record and study the flight behavior of the young eagles in the Central Alps for up to three years.
As the team reports, the data analyses showed how the birds optimize their flight skills over time and can therefore ultimately explore an ever larger area. Gliding, for which the birds of prey are known, plays an important role. In this flight mode, they use air currents with their wingspan of up to 2.30 meters to cover large distances without flapping their wings and therefore with comparatively little energy expenditure. “However, it is not so easy to find these invisible and sometimes treacherous currents and adapt your body to gain altitude,” explains lead author Elham Nourani from the Max Planck Institute for Behavioral Biology in Konstanz.
Patterns in the data now show that the key to the young eagles’ growing success in flying is a steadily improving use of different types of updrafts in their habitat. Young eagles therefore obviously have to refine their innate talent first. Specifically, it was shown that the fully grown young eagles initially limited their flights to the area around mountain ridges after leaving the territory of their parents. As the researchers explain, so-called orographic air currents occur at these landscape structures: wind is deflected vertically at the elevations – the air rises. These updrafts are comparatively easy to predict based on the landscape and are therefore probably initially used preferentially by the still inexperienced golden eagles, explain the researchers.
Learning how to use thermals
However, as the data shows, as the birds get older they increasingly fly into areas where the air flow conditions are not so clearly defined by the topography. It appears that the eagles are increasingly using thermal currents – warm air that rises from flat areas of the landscape. It is likely that this is based on learning processes that lead to a better recognition of the thermally active areas and their use. “In the early stages of their development, the animals may not have the full ability to perceive their environment, as is the case in later stages,” write the authors.
As it turns out, the increasingly “smart” use of air currents is leading to an enormous expansion of the young eagles’ flight areas: their habitat has increased by more than two thousand times within three years, the researchers report. “It seems that even eagles, which seem to move in the air like a fish in water, first have to learn to obtain the energy they need for gliding from thermals,” summarizes senior author Kamran Safi from the Max Planck Institute for Animal Behavior.
As the team concludes, the results have not only biological significance but also significance for eagle management: “We need distribution and movement maps of wild animals so that we can defuse any conflicts between them and humans,” says Nourani. “Our results show that these spaces can change over time. This allows us to make more accurate predictions about where the activity of eagles overlaps with that of humans,” says the scientist.
Source: Max Planck Society, scientific article: eLife, doi: 10.7554/eLife.98818.2