Why can birds without sexual dimorphism distinguish between males and females?

We asked ENRIQUE FONT and he explains that, when we talk about species without sexual dimorphism, we should complete the sentence with a small note: species without a sort of sexual dimorphism that we can detect. The sensory abilities of birds are, in this case, very different from those of humans. For instance, their visual system is much more sophisticated than ours, and that allows them to see much more than the human eye. A good example is the blue tit, with its characteristic blue cap. Several studies have proved that this cap has an ultraviolet light reflectance pattern that we cannot see, but allows the species to distinguish a male from a female clearly from a great distance.

Dimorphism is the product of sexual selection, derived from competition between sexes. Dimorphism is more evident in many species, like humans. But in the case of birds, sexual selection is not so intense, since the survival of these species depends on both sexes.

Enrique Font is professor of Ethology at the Cavanilles Institute of Biodiversity and Evolutionary Biology