03/06/2026
There are a lot of species where the adult males and females look different, this is known as sexual dimorphism. Some famous examples would be peacocks and peahens; the males have the beautiful blue plumage and striking tail, whilst the females are brown all over. Male mallard ducks have a stunning blueish green head and the females are brown. This sexual dimorphism can also be seen in some bird of prey species.
Female adult Eurasian Kestrels are rusty brown all over, whilst the adult males have a blueish grey head and tail. Whilst the males may look prettier, it’s actually not very helpful colouration and is known as a maladaptive trait. This means it is not helpful to survival. The blue feathers make camouflage more difficult, making them an easier target for predators and competition. However, this characteristic does have its silver linings! It can be quite attractive to the females; the blue head and tail signifies a mature and healthy male. The females want to pass on the best genetics onto their young, so by seeing that this male has survived with this maladaptive trait, they must have some pretty good genes. It suggests that they are good at hunting and evading predators as they have been able to survive despite this unhelpful plumage. The female also wants to be provided for and protected, so again, a male who can survive on his own with this trait must be a great kestrel husband. The brighter the blue colouration, the more attractive the male is to the female as it suggests he is well fed.
You may notice that our female kestrel, Nora, looks a bit unusual! She has the typical rust red back, but a blue tail, and no blue head? We assume Nora is female based on weight- in birds of prey, the general rule is that the females are approximately a third of the size larger than the males (another form of sexual dimorphism!). The animal kingdom can be a little bit random, so based on weight and behaviour, Nora could be a female with a weird tail. We could get her DNA checked, but that requires plucking feathers. I personally am not willing to upset Nora, she’s only just started to accept me! -Cerys
📸- Simon Bird
