🪶 Raptor Biology & Terms · 7 min
Sex, size and age class
Why this matters
Every legal question about what you may trap turns on age class, and every practical question about weight turns on sex. These words are not decoration, they are the categories the license is written in.
By the end of this lesson you will be able to
- Explain reversed sexual dimorphism and how reliably it separates the sexes
- Define eyas, brancher, passager, haggard and intermewed
- State why haggards are not taken for falconry
The females are bigger
In most raptor species the sexes look alike in colour, and the reliable difference is size: females are larger. In the bird-eating species the gap is dramatic, with males of some species about one third smaller. That is where tiercel comes from, the male being a "third" smaller.
Not every species hides the difference in plumage. The American Kestrel is the falcon in which sexual dimorphism shows in both coloration and pattern. Adult Merlins also differ by sex in colour, though immature Merlins of either sex look the same. And no common falconry species is entirely without sexual dimorphism, which is why "none of the above are correct" is the answer when the exam offers you Kestrel, Red-tail and Peregrine.
Age classes, which are also legal classes
| Term | Means |
|---|---|
| Eyas | A nestling, and by extension a trained bird of any age that was taken as a nestling. A five-year-old bird can still correctly be called an eyas. |
| Brancher | A young bird that has left the nest or eyrie but stays in the immediate vicinity. In New York you will meet branchers of falconry species in June. Great Horned Owls breed in January or February, so their branchers come months earlier. |
| Passager | A raptor captured on its first southward migration, so a bird in immature plumage and of known age. First-year birds caught in non-migratory situations count as passagers too. |
| Haggard | A wild adult, in adult plumage. |
| Intermewed | A bird that has been kept a full year and molted in captivity. Literally "an interval in the mews." |
Why haggards are off limits
Not because they are old, and not only because they are hard to train. Young birds of prey suffer more than a 70% mortality rate before breeding age. The birds that made it to adulthood are the breeding stock, and the settled consensus of falconers and regulators in the United States is that they stay in the wild. In New York this is not merely an ethic: a falconer who captures a raptor in adult plumage must immediately release it at the site of capture.
From the field
You trap a red-tail in late October. Its tail is brown and barred rather than red, its eyes are pale, and it is clearly a first-year bird. What is it, and may you keep it? It is a passager, in immature plumage, of known age, taken inside the September 1 to January 31 window. As an Apprentice with a sponsor present, this is precisely the bird the license allows. Had the tail been brick red, you would be untying the bird where you stood.
This lesson is part of the NY Falconry Exam course. Open it in the course to answer the retrieval checks that go with it, track what you have read, and quiz the whole unit. Lessons, quizzes and the glossary are free.