In mammals, age-related greying happens when the hair roots stop producing pigments.
It may in part reflect a decline in body condition, but can also signal dominance – think of a silverback gorilla.
In fact many birds, including jackdaws and robins, can go grey too. There’s even some evidence that greying birds make more attractive mates – perhaps because experience is such an important factor in nesting success.
But if greying is less obvious in birds than in mammals, that might be because the colours in birds’ plumage are often produced by the microscopic structure of the feathers, which reflects light at different wavelengths, rather than pigments.