Male and female peregrines look similar, but they are not the same. This is frequently observed amongst birds of prey and is called sexual dimorphism. But what are the differences between the genders?
Firstly, females are significantly larger than males and often appear bulkier as well as bigger, whereas males typically have a sleeker, slimmer appearance. This is particularly noticeable when you see a pair side-by-side but not always helpful if you see a single bird since the peregrine is a large bird anyway. This difference in size between male and female birds, with females being larger, is common in birds of prey but is especially obvious in peregrines.
Interestingly, the old name for a male peregrine was a tiercel, which comes from the Latin tertius meaning a third because male birds are around a third smaller than females. The Normans were great falconers and probably introduced this word into English together with many other words associated with falconry including the word falcon itself, but also lure, gauntlet, haggard, and rouse, which all now have other meanings in English. Common phrases such as being ‘under the thumb’ and ‘fed up’ come from falconry as well.
Male peregrines tend to look neater with more sharply defined markings than females, which can look less ‘tidy’. The yellow colouration of the beak and around the face is often brighter in males than females too.
You can see these all three of these differences in the photos above, taken at about the same distance away. The male is on the left and is (1) smaller and sleeker, (2) more neatly marked, and (3) the yellow bill and face are brighter.
A difference that is particularly apparent in this pair is that the male’s back and head are a darker, bluer, colour than the female which is greyer. This is often the case in peregrines, but it is not a very reliable difference in the field because it is determined very much by the quality of the light, and there is a lot of variation between birds in this respect anyway. The pair shown above are very distinctly different, but often the differences are less obvious and there are plenty of female peregrines that are a lot darker than the one in the photo above.
Another important and more reliable difference between males and females can be seen on the chest. This is sometimes quite difficult to photograph because in the wild, peregrines often like to turn partly away from you so that their dark backs blend into the surroundings, making them less obvious. Males and females both have white throats, and males have a white chest too. However, in females the chest usually has a number of thin vertical dark streaks and sometimes spots, and the chest may also be more cream-coloured. This is shown well in the example photo of a female below.
Finally, in the right light, you may occasionally see a faint pink flush to parts of the underside of the male. It’s well-attested, although I must say that I have rarely seen it myself. Females don’t have it.
I hope that’s a helpful summary. There are a few other websites where photos of individual male and female peregrines are compared and you might like to look at these sites too: