Why do starlings’ beaks change colour?

Acrucial part of avian anatomy, birds’ beaks are used as tools, weapons and much more – including communication. Beaks are formed from the jaw bones, covered with a skin-like layer toughened with keratin, and it is this layer that stores the pigments that provide colour to the beak.

Melanin gives starlings their dark winter beaks, but from November (later in migrant starlings) these start transitioning to yellow, ready for males to establish their breeding territories. This yellow coloration comes from carotenoid pigments, which the starlings cannot produce themselves but instead gain through their diet.

Since carotenoids also play an important role in avian immune systems, the intensity of yellow can be used by starlings as an insight into each other’s condition and potential parenting skills. A nice bright beak suggests a healthy bird. This is known as an honest signal, as the starlings are unable to manipulate its message – they’re forced to show their true colours.