Some lesser kestrel females (Falco naumanni) show male plumage traits, i.e. grey rumps and tails. This phenomenon has seldom been analyzed in birds, and two hypotheses have been suggested to explain it. The first proposes that, when sexual selection acts favouring the expression of a trait in males, females could show the analogous character by genetic correlation (indirect sexual selection). Alternatively, the expression of these traits in females could be favoured by intra-sexual competition or even by male mate choice selecting ornamented females (direct sexual selection). We have tested if females with male traits are favoured by direct sexual selection, through a 3-yr observational study of 239 female lesser kestrels. Our results cannot support the predictions, as females with grey plumages do not achieve access to better breeding opportunities or fitness benefits. These traits do not seem to be honest signals of phenotypic quality, since physical condition and survival did not differ between females which showed male traits and those which did not. The expression of male traits in these females increased with their ages, but showing a high individual variability. Finally, since the genetic correlation hypothesis is unlikely in this species because all males have grey rumps and tails, we propose a new age-related hormonal explanation.