At 9 weeks eaglets begin flapping wings and strengthening themselves for first flights. At 12 weeks they are airborne and practicing targeted flights. Blood in the shaft of the juvenile's new quill feathers does not dry up for over a year and this temporarily inflates their size larger than the mature bird. It is widely believed that eagles mate for life. Eagles have eyesight eight times better than man.
Northern eagles migrate south in winter to habitats in Washington, Oregon and Idaho.
The Skagit area is one of the largest concentrations. Southern eagles disperse north to cooler climates. Migration routes to open waters appear aimless. Juvenals generally migrate farther than adults who may not migrate at all some years. More band return data is needed.