It sometimes seems like female/juvenile Lesser Kestrels and Common Kestrels were "created"* with no other purpose than test our identification skills but at least adult males are, on a decent view, not too difficult to distinguish from one another. What fewer people seem to be aware of is the tricky identification pitfall presented by first summer males.
* Actually that may not be too far from the truth as some scientists believe that Lesser Kestrel, which isn't as close a relation of Common Kestrel as its appearance suggests, has evolved to mimic Common Kestrel and even more so Rock Kestrel, an African species found where Lessers winter, which are both larger and more aggressive thus affording the smaller species' some measure of protection!
* Actually that may not be too far from the truth as some scientists believe that Lesser Kestrel, which isn't as close a relation of Common Kestrel as its appearance suggests, has evolved to mimic Common Kestrel and even more so Rock Kestrel, an African species found where Lessers winter, which are both larger and more aggressive thus affording the smaller species' some measure of protection!
After watching adult males for a while it becomes distinctly less difficult to pick them out thanks to their plain bluish-grey hoods, lack of dark moustache, whitish underwings and particularly their grey upper wing panel. Sometimes, though, these features can prove to be 'false friends' since they lull you into a false sense of security and mean you could be missing first summer males. These birds not only fail to show most of the clear cut identification features of an adult male but, worse, can mimic to some degree the features associated with a male Common Kestrel.
Illustration 1 : 1st summer, note the tail & head pattern, lack of grey wing panel and lack of grey wing panel, Fortunately, though, most young males (of both species) have a distinctive tail which should alert you to the fact that you're dealing with a potentially difficult identification. Whilst all juveniles start off with a barred brown and black tail (like a female) by the time the young males return in the spring, the central feathers are grey and black tipped (like an adult's) and the outer feathers a very worn and bleached brown and black. This feature should warn you that you're looking at a tricky first summer birds (although later in the season they may have a fully adult tail). The problem is that such birds entirely lack an adult male's tell-tale grey band on the upperwing so that if you're relying on this feature you can be misled. If you then check the bird's identity by looking for the male's plain bluish-grey “clean shaven' head then you can still be thrown. Males at this age not only may have their powder blue-grey heads sullied with brown giving them more the colour of Common at a distance. Not only that but they can also show a Common's dark moustache and paler cheeks! This is compounded by their tending to have more dark makings on the chest and underwing than adult males. Put all of these together and it's easy to see why, at a glance, you might identify one as a Common Kestrel.
Fig 1: Common Kestrel (left), Lesser kestrel (right) So how can you tell them apart?
Happily, when perched, first summer has the Lesser's typical dumpier, more round headed shape with wings that approach the tip of the tail (see Fig 1). At times this can look obvious but at other times it's not so easy to detect particularly if you're unfamiliar with the species. Then there's also the distinct wing formulae with Lesser having a far longer outermost primary (P10) although that's best seen in photos of flying birds (see Fig 2)
Fig 2: Note that in Lesser P10 is much longer than P7 whilst in Common they're the same length Leaving aside structure, then the best indicator is that the birds have at least moulted their back (i.e. mantle) which are plain and unmarked. Also although streaked below the markings are still fewer than on a Common Kestrels and more round in shape whist the ground colour tends to be warmer. Similarly the underwing, although more marked than most adult males, are still noticeably paler and whitish (particularly the 'hand').Other features to look for on perched birds are the famous white claws and Lesser's more dumpy appearance and wings that reach further towards the tail tip. In photo of flying birds, of course, the distinctive difference in wing formulae can be seen.
Illustration 3 : First summer male Lesser Kestrel - note the streaked nape, darkish moustache, pale cheeks and crown sullied with brown which make this bird resemble Common Kestrel
So if we may be missing the odd first summer male, how else are we missing them? Well, many people still fail to appreciate that some Lesser Kestrels don't migrate but remain in Spain during the winter months. If you're not looking for something, they're easier to miss! As a general rule most Lesser Kestrels leave southern Spain in August - September (with a peak at the end of the latter month) with a few lingering into October. Although in spring most appear to arrive in the second half of March, in Alcala de Los Gazules I've had evening flocks 60-70 or more by mid-February and friends report influxes as early as January. Although the picture is muddied by late departures and early arrivals, some birds don't seem to leave at all. Exactly how many remain remains a matter of debate.
The Spanish winter bird atlas shows concentrations of wintering birds along the Guadalquivir particularly in its lower reaches, east of Seville and around Cordoba plus several other areas. Both my own experience and that reported in the atlas suggests that birds are generally seen when they return every night to a traditional colony site or when they leave every morning. The atlas also quotes a study (Negro, Riva & Bustamante: Patterns of winter distribution and abundance of Lesser Kestrels in Spain. Journal of Raptor Research, 1991: 25: 30-35) that discovered that wintering birds were found in 66% of the colonies checked and that the authors concluded that in Andalucia 19% of the species is sedentary, a surprisingly high figure. Interestingly, although the atlas doesn't show Alcala de los Gazules as a wintering site in my limited experience a few birds do actually remain around the village in winter albeit no more than a than a dozen or so. Most of the birds I've seen have been adult males but in rather smaller numbers than reported by Negro et al., being between 5-10% of the numbers I see in the breeding season. However, from this I suspect that wintering birds are a little more widespread than the atlas shows. Even if the estimate that 19% stay is a little high, my much lower 'guestimate' of 5 - 10% suggests that well over 1,000 birds might be there to be found!
So if you're in Andalucia in winter remember that Lesser Kestrels return earlier than you might think and don't give up on seeing Lesser Kestrel even in mid-winter. So double check those kestrels you see out hunting in November-January and try to visit a lowland village with a thriving summer population just before dusk.
This is a much shortened and amended version of a short article on Lesser Kestrels due to be published in the magazine of the Andalucian Bird Society's quarterly magazine in autumn 2016 (see - www.andaluciabirdsociety.org/)
So if you're in Andalucia in winter remember that Lesser Kestrels return earlier than you might think and don't give up on seeing Lesser Kestrel even in mid-winter. So double check those kestrels you see out hunting in November-January and try to visit a lowland village with a thriving summer population just before dusk.
This is a much shortened and amended version of a short article on Lesser Kestrels due to be published in the magazine of the Andalucian Bird Society's quarterly magazine in autumn 2016 (see - www.andaluciabirdsociety.org/)
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