How do we know falcon Zooey’s age?

How do we know that falcon Zooey is two years old? Peregrine falcons have two distinct age-related plumages: juvenile and adult. Juvenile falcons have heavily barred underparts and brownish topsides (“brown birds”), mature falcons have pale undersides with black-barred bellies and blue/slate topsides (“blue meanies”), and two-year-old falcons like Zooey have a mix of adult and juvenile feathers. I love this stage!

Tail Feathers (Retrices)

Like all peregrine falcons, Zooey has twelve tailfeathers that are numbered one to six from the two symmetrical deck feathers at the center of her tail.  If you look closely, you’ll see that her right-side R3 feather is browner and more ragged than the rest of her grey-and-slate white-tipped tailfeathers. Tailfeather molt in raptors almost always begins with their central or deck feathers (R1), followed by R2, R6, R3, R4, and R5 on each side. It’s a little unusual that Zooey replaced R4 and R5 before R3, but tailfeather molt is more variable and asymmetrical than wing feather molt.

Primary and Secondary Wing Feathers (Remiges)

Let’s talk about Zooey’s wings! Falcons have 10 primary feathers that are numbered down from the top (P10) to the bottom (P1). These rigid, controllable feathers provide most of a falcon’s forward thrust and are more asymmetrical towards the leading edge or top of its wings. Falcons replace their primaries in two directions: from P4 inward to P1 and from P4 outward to P10, sometimes replacing P4 and P5 at the same time. Wing molt is very symmetrical: birds replace the same feathers at the same time on either wing. Based on what little we can see of her wings, it looks like she has yet to replace P6 through P10, but we can’t be sure given that we don’t have her in hand.

Like all falcons, Zooey has 13 rounded, symmetrical secondary feathers. These feathers overlap, giving her the lift she needs to stay aloft during flight. They are numbered inward from S1 to S13, the wing feather closest to her body. Falcons also replace their secondary feathers in two directions: inwards from S5 to S13, and outwards from S5 to S1. Zooey’s S1 feather is still brown, which isn’t surprising: S1 is often the last secondary feather that falcons replace.

Body Feathers (Coverts)

Raptor Identification, Ageing, and Sexing tells us that raptors begin molting 7 to 10 months after fledging. Molt starts at their heads and proceeds down through their bodies. No particular order is given beyond that, but Zooey is clearly molting from her head on down.  Note that she still has the pale ‘eyebrows’ we sometimes see in younger birds.

How do Zooey’s feathers compare with mate Newman’s? We get a very nice look at them in this video!

Understanding when and in what order falcons, eagles, and hawks replace feathers can teach us a lot about molt, even at a distance!  If you’d like to learn more, check out these resources:

  • In-Hand Guide to Diurnal North American Raptors. Hawkwatch International published this guide for banding station staff. It is not a ‘read’ in the usual sense of the word, but has invaluable information about identifying, aging, sexing, and properly documenting raptors.
  • Raptor Identification, Ageing, and Sexing: This is another excellent guide! It doesn’t have many photos, but has excellent information on plumages, field guides, the use of molt as a tool in ageing, and the use of behavior in field identification.
Did You Know?
  • I used ‘R’ numbers instead of ‘T’ numbers for Zooey’s tailfeathers because the In-Hand Guide to Diurnal North American Raptors uses R (for retrix). The Guide has set the gold standard for identifying, sexing, and aging raptors in the field and we will be using their format from here on out.
  • Birds can control and rotate their primary feathers like fingers, changing their body shapes, trajectories, speeds, and flight styles literally on the wing! Unlike other feathers, remiges are anchored to bone with strong ligaments so they can withstand the demands of flight and be precisely positioned. Learn more about them here: