Bluetit factoid

Most birds can’t create pigments, other than melanin, on their own. This bluetit, high in the park’s canopy, can’t produce the pigment, carotene, that makes his tummy yellow; it comes from pigments in the green caterpillars he eats. The more caterpillars he eats and the brighter his tummy, the more likely he is to attract a mate.

Header picture by DKG; others CC0 from pixabay