There is quite a big difference in size between the tiercel and falcon. Tiercel in French means a third and therefore the male is a third smaller than the female. This size difference is common in all birds of prey and is called sexual dimorphism. It is even more acute in the peregrine falcon than any other falcon. You can really see the difference in size when the pair at the Falls of Clyde sit near each other on their favourite branches on the oak tree above the eyrie.
The other differences are the falcon at the Falls of Clyde has a long dark moustache and distinctive white cheek patches whilst the male has a dark hooded appearance and no cheek patches and a short moustache. The male’s upper beak and talons tend to be a brighter yellow than the females. He also tends to look a bit smarter than the female. She always looks a bit ruffled and scruffy.
Tom – Species Protection Officer