Humans are typically attracted by unusual, extravagant things that stand out in the crowd23. In the case of birds, ornamented species (e.g., with a long tail or long crest), or species which are more colourful and brighter coloured8,12 are more attractive to humans. Furthermore, species with brighter (lighter blue, see Supplementary Fig. 1) and more elaborated colours (unusual colours departing from brown-grey) are the most attractive to humans (Fig. 2). Overall, such findings of higher attractiveness for birds with less common features, be it ornaments or colors, also align with the negative frequency-dependent selection theory in humans24. The latter postulates that a preference for rare phenotypes is a type of selection that contributes to maintain rare alleles from being lost. This theory may, at least partly, explain the aesthetic preference we found for the rarest colors, like red and blue, and ornaments, such as long tail and crest. This is further supported by our result on the significance of color elaboration (i.e., rare colors departing from the average brown/grey), which was the variable with the strongest positive association to attractiveness among all those considered (Fig. 2). Further studies are needed to experimentally quantify the contribution of the above theories in shaping our aesthetic attractiveness for birds beyond the correlational evidence shown here (e.g., see ref. 28).