In the field, I saw its short P10, and immediately jumped to the conclusion that it had to be a Common Kestrel.
I quickly took one photograph and thought no more of it. There were many Lesser Kestrels around, and these were my main focus at the time.
When I looked at the photo at home, however, it became clear that a number of things are at odds with Common Kestrel, even though the wing formula and the pattern of the remiges strongly suggest this species, and are very wrong for a male Lesser Kestrel in autumn. I guess it is mainly the lack of black spots on the underparts that is outside of the variation seen in male Common Kestrel, but added to this are some more subtle differences:
- grey cheek
- lack of blackish moustache
- unmarked white ‘boomerang’ around the wrists
- not much pattern on the underwing coverts, including axillaries
- a rather rounded, bulbous head
- rather fat body and broad tail base
- very big white tips to the tail feathers
Wouter Faveyts and Andrea Corso have been very helpful in discussing this bird (on the basis of the single photograph). From our e-mail correspondence, it is clear that the bird can be aged as an adult male: all remiges are of the same generation, and the tail pattern is obviously not that of a juvenile as it does not show even a hint of barring. Birds in the autumn of their 2nd calendar year either show different generations of flight feathers (usually 9 adult primaries and 1 juvenile, outermost, after arresting their moult) or a complete set of adult primaries (with the typical, unbarred pattern). In any case, the pattern of the remiges is wrong for any Lesser Kestrel, particularly males, as they show a broad dark trailing edge to the secondaries, which this bird lacks.
Eastern Lesser Kestrels may show a bit more strongly barred remiges than western birds, but they still have the broad dark trailing edge on the secondaries, and besides, an adult male would not show such extensive Common Kestrel-like barring (nor short P10). They also tend to have darker head and body, the latter with rounded black spots – which are absent in this Armenian bird.
In conclusion, the wing formula and pattern of remiges suggest Common Kestrel, while most other characters suggest Lesser Kestrel.
The most logical conclusion, hence, is that this bird is a hybrid.
The people from the Armenian Society for the Protection of Birds, who ring chicks of Lesser Kestrels every year, have told me that they have seen a few suspected hybrids in the main colony over the years, but they have no photographs. There are only two colonies of Lesser Kestrel in Armenia, and Common Kestrels breed in at least one of them too. Though the two species are genetically distinct and have very different calls, I guess rare cases of hybridisation may occur. Hybridisation (in nature) is mentioned in Panov (1989). Hybridization is said to have occurred in Italy too, though there is no documentation of this.
Though it is unfortunate that there is only one photograph, this may be the first documentation of a hybrid kestrel.