Female Eurasian and Lesser Kestrels are harder to separate but straight forward with practice - the wing formula (ie the shape of the wingtip formed by the respective length of primary fingers in relation to each other) is diagnostic, giving Lesser Kestrel the impression of a more rounded wing when hovering. Also, the tail of a Lesser Kestrels is proportionately longer (noticeable on a perched bird) and mantle pattern and underwing pattern are different (the latter on Lesser Kestrel being less boldy marked). Female Lesser Kestrel often have a noticeable moustache as with European Kestrel which (in the case of males too) can be ‘artificially enhanced’ by light/shadow) although is never as long or distinct as in European Kestrel but both female and male Lesser Kestrel lack the diagnostic dark ‘eyeshadow’ that extends in a line from the rear of the eye. Overall proportions in flight are also different to a trained eye, Lesser Kestrels being more ‘dumpy” than European. In European populations, European Kestrel tend to be sedentary whereas Lesser Kestrel are migratory - the latter breeding in colonies and congregating in flocks before migrating - which can add weight to identification also, especially at certain times of the year.
edit. forgot to add, (because I haven’t had my second cup of coffee yet!), the claws of Lesser Kestrel are paler/horn coloured whereas on European Kestrel, the claws are very dark grey/black. It’s debatable how useful this in in the field imo as wet claws can reflect light and are often muddy or generally discoloured with dust etc. On very good views though, and on half decent photos, it’s usually diagnostic.
