The following guidelines reflect our interpretation of Cramp et al. (1985) and Baker (1993) and the criteria may be open for discussion. Most individuals apply to the descriptions below (and make sure to check all characters), but intermediate birds do occur and should be left undetermined.
Male (1cy) October. A rather typical male showing whitish lesser underwing-c (with a limited presence of beige or sandy hue). Note also lack of dark markings to the tips of underwing GC and PC. 
Male (1cy) October. Some males show more sandy hues in the underwing (e.g. in the SS), as well as weak dark arrow-shaped markings to the tips of underwing GC and PC. But most are still rather pale and dominantly whitish in the anterior underwing-c. Difficult birds do occur, and should be left without sex. 
Male (2cy+) November. Another typical, pale whitish, male. Sometimes, like here, a weak pinkish (or even greenish) hue is visible in the underwing. 
Female (1cy) October. Typical females show a rather deep sandy or buff colour to the underwing-c. Many, but not all, females also show distinct dark markings to e.g. tips of the underwing GC and PC. 
Female (1cy) October. A clear variation is seen, and some females are rather pale (but note the still rather extensive sandy hues to the underwing-c). In more difficult individuals (like this one, which also lacks darker markings to the coverts) it is important to check several characters, and some should be left without sex. 
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