As one who has been an avid birder for more than 40 years, I have seen hundreds, if not thousands, of bald eagles, primarily during my years in Missouri. It was thus easy for me to identify an immature bald eagle as it flapped its way across the South Platte Valley this morning.
Heading for a large, barren cottonwood, west of Eaglewatch Lake, the young eagle joined another large raptor that occupied one of the limbs. At first, I assumed that the other predator was a light colored red-tailed hawk that has visited the refuge throughout the winter; after all, its wings and back were brown in color and its head was dull white. Zeroing in with my binoculars, I was surprised to find that it was another bald eagle, different in appearance from any that I had seen over my birding career.
Approaching on the lakeside trail, I got a close look at what appeared to be a dull, sooty adult bald eagle, its white head speckled with gray blotches. It was, in fact, likely a three or four year old bird, having molted from its dark immature plumage but not quite festooned with the regal coat of a breeding adult. Once fledged, young bald eagles retain their dark feathers, broken by a variable pattern of white markings on the wings for at least two years; a gradual transition to the mature adult plumage occurs during the third and/or fourth year. An eagle with a bright white head and tail and dark wings and torso is thus at least four years old; breeding capability coincides with achieving mature plumage. While both juvenile and adult bald eagles have yellow feet, juveniles have a thick gray bill that takes on a bright yellow color as they mature.