Thursday, October 21, 2010

A Comparative Field Guide

Common Kestrel - juvenile
Andalucia, the most southern part of Spain, is an extremely special place for birds. A great many species, rare or even absent in northern Europe, visit this birding Mecca either as a migrant or to find safe and specialist areas to winter or breed. Unsurprisingly the region attracts a great many birders from around the world and can offer challenges to even the most experienced birder, resident or visitor!
Among the species that regularly cause identification problems, for example, are Pallid Swift, Thekla Lark and Lesser Kestrel. These species are particularly difficult due to similarities with closely related birds i.e. Lesser Kestrel and Common Kestrel. On behalf of the Andalucia Bird Society I will be publishing various identification guides for these more difficult birds in the future and hope members of the society and visitors to Spain will find them useful and of practical assistance when out in the field watching birds. For now, I help discribe the key feature that help distinguish Lesser Kestrel from the more widespread Common Kestrel.

Lesser Kestrel male (left) - Common Kestrel male (right)
The photograph, Figure 1, to the right shows an adult male Lesser Kestrel (left, LK photo Juan Luis Muñoz) and an adult male Common Kestrel (right). Simple enough to see the difference, but in the field it can be hard to separate them. The females and juveniles can sometimes be nigh impossible, even for the most experienced observer. As well as giving comparative detail of these 2 species for the Andalucia Bird Society, I have also given species accounts and descriptions, hoping that the combination of information will help those who find these particular birds hard to separate.

Flight identification. Lesser Kestrel when soaring shows more rounded wings than Common Kestrel, also whilst soaring or hovering it appears to be bulkier in the body, both sexes appear paler on the underwing, the male very markedly white compared to dark breast and with more distinct black wing tips. In flight and more especially when hovering, Lesser Kestrel show wide and triangular tail-band, Common Kestrel nearly always shows fan-shaped tail-band. In silhouette the bulkier and shorter body is useful to distinguish both sexes and juvenile Lesser Kestrel from Common Kestrel. When hanging in a headwind Lesser Kestrels give the appearance of a small Peregrine with their shorter tail, plump body and pointed wings swept back in scimitar shape. Of course the male Lesser Kestrel has very distinctive features such as grey head, little or no moustache stripe, grey upperwing coverts (remarkably difficult to see at a distance) and with spotless upperparts. Photograph to the left shows Lesser Kestrel male, note the triangular black terminal band.
Author's note: Whilst watching flying birds always stay focused and wait for the bird to spread its tail, either when it pauses to hover or using it to manoeuvre, it is then possible to view the shape of the black subterminal bar to tail, a very useful aid to successful id. Plumage differences are discussed below.

Claw colours
Identification of perched birds. See Figure 1 for comparison of both species of male. A good guide is Lesser Kestrel can be distinguished by longer wings, either reaching or nearly reaching the tip of the tail. Caution is necessary though for 2nd year birds in spring that may have replaced their tail with longer feathers! The normal upright posture of both these Kestrels will normally allow the observer to see the wing length in relation to tail tip. Claw colour is another very positive, although sometimes difficult to see, identification feature; very pale or grey with Lesser Kestrel and black with Common Kestrel. Adult male Lesser Kestrel have spotless upperparts with part grey upperwing coverts and tertials; head is uniform grey, but can occasionally show a faint moustache, never with pale cheeks as with Common Kestrel. Both females and juveniles can be separated from Common Kestrel by head pattern and feather pattern to upperparts; head is plain except for dark moustache below the eye and pale cheek patch reaching the crown, no dark eye-line as in Common Kestrel; upperparts finely barred i.e. much narrower than rufous interspaces.

The above is an extract from A Comparative Field Guide written by Peter Jones for the Andalucia Bird Society. Work is in progress to include additional pages for Thekla Lark / Crested Lark, Pallid Swift / Common Swift. Plans are well advanced to do similar pages dealing with the complicated Sylvia group of warblers, especially the females and juveniles, Sub-alpine Warbler, Spectacled Warbler and Sardinian Warbler are all members of this group which can present challenges in the field. If you live in Spain or plan to visit why not join the ABS and enjoy free access to the completed article and other useful resources of the Society? For more information follow this link.

I hope the reader may have found this blog article of some use! Peter.

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