This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: When a young golden eagle (Aquila chrysaetos) finally leaves its parents' territory, it leaves behind the only safety net it has ever known. Until now, biologists had assumed that eagles took this step as soon as they could fly well enough to survive on their own.
However, a new study, in which 92 young golden eagles in the Alps were tracked using GPS transmitters over six years, shows that flying ability has almost nothing to do with it. Just a few months after young eagles fledge, they can fly just as skillfully—climbing rapidly, circling in tight radii while soaring on thermals and making use of shifting winds—as adult eagles. Nevertheless, many remain in their parents' territory for almost a full year afterward.
"Golden eagles seem to be able to fly well long before they leave their parents' territory," says Hester Brønnvik, lead author of the study and a scientist in the Department of Evolutionary Ecology at the Leibniz Institute for Zoo and Wildlife Research. "Being able to survive on one's own and actually taking that step are clearly two different things." The paper is published in the journal Royal Society Open Science. Between 2019 and 2024, the team fitted young golden eagles in the Alps with GPS tags and tracked each bird's movements from the age of around 50 days—that is, shortly before it left the nest—during its first forays outside its parents' territory and, in most cases, right up to the day it finally emigrated.
Most eagles undertook their first journey outside their parents' territory within about three months of being tagged, covering distances of up to 77 kilometers (48 miles), sometimes on excursions lasting several days. Studies from other regions suggested that golden eagles reach their full adult flying ability at precisely this age. However, this was not followed by emigration; many birds did not leave their parents until almost a year after being tagged, often only after winter had ended.
"These young eagles were clearly capable of surviving outside their parents' territory long before they actually left it," says Brønnvik. "They were already undertaking flights of dozens of kilometers and staying away for days at a time. They simply kept coming back." To analyze their flying abilities, the transmitters sent short bursts of GPS data at a resolution of one location per second.
This enabled the scientists to reconstruct exactly how each eagle soared: how tightly it circled in thermal updrafts, how quickly it gained altitude and how well it coped with the wind. The team wanted to know whether the birds that mastered flying in thermals the quickest were also the ones that left home the earliest. "These skills proved to be necessary, but were by no means sufficient," says Elham Nourani of the Max Planck Institute for Animal Behavior and the University of Konstanz, one of the study's lead authors.
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