Help with Cooper's Hawk age

I am trying to get a better undstanding of how to determine the age of the Cooper's Hawks that come by the water trays we leave out in the desert behind our place. I know the juvenile has white vertical streaking underparts with yellow eyes (1st or 2nd year?). Some have orange eyes or red eyes with a darker orange horizontal streaking (3rd or 4th year adults?). I have posted 4 different Cooper's in the following images and I am curious about their ages.
Thanks for any help on this.
Regards,
Jim

1st hawk

2nd hawk

3rd hawk - this hawk is the largest of all the hawks including the older hawk with orange eye.

4th hawk

Even my two guides to hawks (both by Bill Clark and Brian Wheeler) don't provide info on aging other than the obvious streaking vs barring, head color, and eye color. Adult eye color goes from orange to red as the bird ages; juvenile birds have pale greenish-yellow to yellow eyes. They don't mention it but birds just out of the nest have pale blue eyes.

Your first three images are juveniles; the last image is an adult.

There are a couple extremely detailed books used by bird banders that might give more information but I've never bothered to get them.

Edited: I managed to skip the third image in my reply and clarified my response to avoid any confusion.

Peter Pyle has written a two volume set of guides to aging birds. Pyle is relied upon by bird banders to ID gender and age in captured birds. But Pyle's techniques are really only useful if you are a bander and have the bird in the hand.

More generally, the on-line Birds of North America is authoritative and well worth the modest subscription price.

Peter Pyle - that's who I was thinking of but couldn't conger up - Thanks Jim.

Thanks Rich and Jim. This is the second year in a row that I see a lot of Cooper's activity in the desert behind our place. Around mid August and for the next 4-5 months they will be around then they seem to move on. On my walk this morning I was watching 2 juveniles fly from tree to tree harassing the Gambel Quails.

First off, I’ll make a plug for the Pyle guides. They’re definitely not for everyone—they are incredibly dense, with lots of abbreviations, almost more like reading a code than a sentence—but they can be very useful to any birder. They are especially valuable to the bird photographer, who (like the bird bander) has the opportunity to see exceptional plumage detail which is not visible in the field under most circumstances. These details can provide insight into age, sex, molt, and all sorts of cool stuff.

As an anecdote, I learned from the Pyle guides to tell 1st winter ravens from adults by looking for molt limits in their greater coverts. This was cool, because when I saw a raven playing with chunks of snow, I looked closer and saw it was a 1st winter bird, playing with the first snow it had ever seen. Cool!

The following applies equally well to ageing both Sharp-shinned and Cooper’s Hawks.

First of all, size has no bearing on age. When a bird takes its first flight, its overall dimensions are essentially the same as an adult (this goes for all species). It may be a bit more slender or lighter-weight, but its size is full-size. In fact, many juvenile/immature raptors have longer flight feathers (wing and tail) than the adults, making them appear slightly larger/lankier. In the case of these species (and many hawks) size may provide a clue as to sex, not age. Females of these species are larger than males.

Briefly, immature Coops/Sharpies are brown with brown streaks on the breast and yellow eyes; adults are gray with orange bars on the breast and red eyes.

First calendar year: both accipiters have a brown overall plumage. Brown on the back, brown vertical streaks on the breast. In a very young bird the iris is gray, then turns yellow.

Second calendar year: The iris gradually transitions to a more orange color. Some bluish gray adult feathers may begin to appear at just about any time. Prior to molt, a 2nd calendar year bird may look very much like a 1st calendar year bird, but the 2nd year bird will show more worn plumage and probably an oranger eye. In late summer, the bird undergoes a complete (or nearly complete) molt into adult plumage, slaty gray on the back (females may be somewhat browner) with orange horizontal barring on the breast. An adult’s iris is red (in a Coop it may be an orangey red).

Once the bird is in adult plumage late in it’s second year, it’s difficult to do any reliable further ageing, but a bird that has a few retained brown juvenile feathers or a yellower orange iris during fall or winter would be a second calendar year bird, and then into the following spring and summer would be third calendar year (but use caution in making these determinations, especially on eye color alone, which can be variable and tends toward being sort of oranger red in adult Coops than in Sharpies).

With all that said, your first three are immature (1st or 2nd calendar year) and the last is in adult plumage (2nd calendar year or thereafter).

Another book to look at is Hawks from Every Angle - may not give you specific years in age but gives a lot of info regarding clues to determine adults and male/females

Here are two photos of a 2nd calendar year Cooper's Hawk that has nearly completed its molt into adult plumage. The photos were taken on 27 Aug 2010.

The photo above shows the orange barring on the breast and gray back of an adult. The iris is quite orange, and will probably get a little redder. If you look very closely at the secondaries (on the lower portion of the right wing), you can see a mix of fresh adult gray feathers and some older, browner, heavily worn juvenile feathers. A few brown feathers are still showing in among the other gray feathers on the wing coverts also. Notice the very fresh unworn white tips to the tail feathers, and that one of the outer tail feathers is shorter than the other, suggesting it is still growing in. Among the breast feathers, look closely and you'll see at least two remaining feathers with brown vertical streaks among all the new ones with orange horizontal barring.

a second view of the same bird, showing a few worn brown juvenile feathers among the fresher gray adult ones.