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The article offers information on adult Golden Eagle with very pale ventral plumage unlike any Golden Eagle has described by science and the bird was hatched in 1997 at a cliff nest in southern Norway. Topics include the photograph of its dorsum its emerging hackles appeared paler than normal for nestlings in northern Europe, and the same bird has been photographically documented at a winter feeding station since 2008.

From nearly 600 prey remains collected in 95 nest visits from extreme eastern to extreme western Mongolia, we found that Golden Eagles (Aquila chrysaetos) consumed a high percentage (20%) of predatory birds and mammals. The prey delivered to nests was also very diverse. As expected, the eagles preyed on hares (Lepus tolai, 12%) and marmots (Marmota spp., 38%), but 15% of their prey were foxes (Vulpes spp.). We identified 30 species of birds, including six species of raptors, among the prey remains. Surprisingly, ground squirrels (Spermophilus spp., 5%) were underrepresented and even in vole (Lasiopodomys and kin) irruption years/zones, voles and other small rodents (4%) were seldom found in the nests. Loss of rodents and other prey due to aerial broadcasting of rodenticides likely affects Golden Eagles in Mongolia, as do persecution, mortality from electrocution, and removal of eagles for falconry and tourist trade. All these need careful quantification. [ABSTRACT FROM AUTHOR]

During seven expeditions across Mongolia, we found 40 Golden Eagle (Aquila chrysaetos) breeding territories with eggs or young. At 20 other locations, we either found old eagle nests with Golden Eagle feathers or saw adult eagles but found no eggs or young. Golden Eagles nested in all but the driest portions of the Gobi Desert and the easternmost grasslands. Nearly all pairs had alternate nests. Of 53 nests used, 60% were on cliff ledges as is typical around the world. However, 19% were on the ground or at other sites that were easily accessible to canid predators, with the most vulnerable nests small and seldom or never reused. The most unusual nests included one atop a conical basalt peak, one on relatively flat ground among tall boulders, four on steep hillsides, one on almost flat ground amid rocky protrusions, and three on cliff tops. Where tall cliffs with many ledges were available, the eagles nested at least 7 m above the ground. Nest construction materials were often unusual and included trash, patches of large mammal hides, paper money, and clothing. [ABSTRACT FROM AUTHOR]

Because many species of large birds must remain capable of flight during moult and breeding, complete replacement of all flight feathers often takes two or more years, with the result that their plumage normally includes many faded, worn and sometimes even broken feathers. It seems adaptive for such birds to have the ability to quickly replace severely damaged feathers. In search of such a feather replacement mechanism, we cut rectrices on a captive Golden Eagle Aquila chrysaetos and found that feathers cut in their first year of use were replaced, on average, after 11.4 months, whereas uncut feathers before and during the experiment were moulted, on average, after 24 months of use. Feather cutting advanced moult, on average, in excess of a year and thereby demonstrates the existence of a previously undescribed neurophysiological mechanism for preferentially replacing damaged feathers. [ABSTRACT FROM AUTHOR]

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The article discusses the study on the uniqueness of color patterns in raptor feathers. The researcher collected feathers from a Golden Eagle held in captivity long term, beginning when the bird was 24 years old and from a second captive Golden Eagle over a 3-year period, beginning when it was in juvenile plumage. The study also examined molted feathers from three captive adult Peregrine Falcons and feathers from other raptors. The results of the study show that complex patterns are not identical for either sequential feathers or symmetrical pairs, while simple patterns are more closely duplicated than complex patterns. It also demonstrates that grossly abnormal feather can be safely used to identify an individual raptor.

From a year-long study of molt in the golden eagle Aquila chrysaetos, we recorded 2069 contour feathers replaced in 137 d (6 May-19 September). Very few contour feathers were lost outside this period. From precise daily counts of feathers lost, and using time series analysis, we identified short-term fluctuations (i.e., 19-d subcycles) around a midsummer peak (i.e., a left-skewed normal distribution). Because these subcycles have never before been reported and because the physiological basis for many aspects of avian molt is poorly known, we offer only hypothetical explanations for the controls responsible for the subcycles. [ABSTRACT FROM AUTHOR]