Mystery bird: Greater spotted eagle, Aquila clanga

Greater spotted eagle, Aquila clanga, (synonyms, Aquila maculata and Ictinaetus clangus) Pallas, 1811, photographed at Mai Po Wetlands, Hong Kong, a Special Administrative Region of the People's Republic of China.

Image: Marie-Louise Ng, 3 November 2011 (with permission) [velociraptorize].
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Question: This Chinese mystery bird is difficult to identify for a number of reasons. (why?) But I am going to put you through your paces whilst I do my homework on this bird: can you identify this bird's taxonomic family and species?

Response: This is a greater spotted eagle, Aquila clanga, a member of Accipitridae; the hawks, eagles, kites, harriers and Old World vultures. Aquila is where the "true eagles" -- those that hunt large prey -- are placed, but this genus is paraphyletic and thus, is not a natural group. It is likely that the greater spotted eagle, along with its sister species, the lesser spotted eagle, A. pomarina, and the recent split, the Indian spotted eagle, A. hastatato, will all be removed to either Lophaetus [doi:10.1007/s10336-005-0083-8] or Ictinaetus or may perhaps placed into their own genus.

Based on its colouring, this is obviously one of the "brown Aquilas" -- lesser or greater spotted eagles or steppe eagle. All of these species show a lot of variation in plumage colouring and patterns between and within age-class. However, that said, possibly the most reliable field mark for these species, regardless of age, is the barring of the remiges, the large flight feathers of the wing.

Based on plumage characters, including the wing barring, we can easily rule out the steppe eagle, which has few and sparsely spaced bars on each feather compared to the spotted eagles.

The lesser spotted eagle has a paler head and wing coverts, compared to the generally darker greater spotted eagle. The lesser spotted eagle has uniform and dense barring along the length of its primaries, whereas the greater spotted eagle has much finer barring that is mostly limited to the middle of its primaries, leaving the tips and base of the feathers unmarked. As with other large eagles, it is possible to determine this bird's age based on plumage markings (for example, only juveniles have the characteristic white spots that gave it its common named), but I know my limits, so I defer my attempts to "age" this individual to those who actually know this species.

The greater and lesser spotted eagles apparently also have some trouble distinguishing species, because they occasionally hybridise in the wild.

Here's a video of a young greater spotted eagle that wintered in Tuscany (the music is horrible; I suggest you turn the sound off for this one!):

Visit GuidoeAnna's YouTube channel [video link].

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