Blackstone Edge

Kestrel male

In flight in dull conditions I often find I cannot sex a Kestrel. Helpfully perching, this bird's grey head and prominent moustache are clear, although the grey is quite pale and might be difficult to see in flight. And the back has spots not bars. But books often say a male Kestrel's back is brick-red, and that's not the case here: it is the same brown as a female's back. Do colours darken as a bird ages?