Blog

Sub-adult Accipiters?

posted by Jerry Liguori at
on Thursday, June 13, 2013 

A bunch of people have sent me photos asking about "sub-adult" accipiters. The term "sub-adult" can be a confusing term because it is used in various ways depending on what you read or hear, and can have more than one meaning. So I thought I would discuss the term in regards to accipiters (and certain buteos). Also, some references have conflicting definitions or usages of certain terms, so my posts are my opinions/thoughts (although some things are plain fact). And, my goal is to try and keep things simple and easy to understand.

To state bluntly, there is no such thing as a sub-adult accipiter. Accipiters show either a ”juvenile” (1st-year) plumage or “adult” (2nd-year and older) plumage (this is also true for most raptors, i.e. Red-tailed Hawk). The adult plumage is acquired after their first molt, which starts at about one year old and takes several months to complete. Some birds retain a few juvenile feathers after their first molt, but these birds are not “sub-adults”. They are adults, since they are in adult plumage. Besides, there are many birds that don’t retain any (or any obvious) juvenile feathers in their first adult plumage. A juvenile in summer going through its' first molt that has a mix of adult and juvenile feathers is still not a sub-adult. They are birds in "transition" or "molting juveniles". A true sub-adult raptor shows real and certain plumage differences from juvenile and adult. They may not appear completely different, but have basic differences that are diagnostic. For instance, Swainson’s Hawk has a sub-adult plumage that always differs from juvenile and adult (albeit, not greatly).

Be very careful of telling retained juvenile from retained (old and faded) adult feathers, I would be wary of distinguishing these without practice! Knowing molt patterns and sequences helps greatly in confirming ages based on the presence of retained feathers. Eye color can be an indicator of age but not a criteria when used alone for ageing raptors. Eye color usually changes quicker in males than females or between individuals. And eye color tone and rate of change varies between buteo species. For instance, Swainson's, Broad-winged, Red-shouldered, and Rough-legged Hawks tend to turn from pale to dark brown quicker than Red-tailed Hawks...and Ferruginous Hawks take quite a bit longer than all of them.

This "sub-adult" issue has come up more recently due to all the close-up photos on the internet, but seeing this stuff in the field or in flight is much more difficult, and sometimes impossible. Take a look at the birds below, some have a few retained juvenile feathers, some have none, some have 2 generations of adult feathers, some have pale eyes, and others have darker eyes. Would you be able to age these? How about in flight? The particular age of each bird below is less important than the fact that they are all in adult plumage.

And, one question: Why does the term "sub-adult" seems to be used frequently on the internet for accipiters, but no one seems to call a Red-tail with a few retained juvenile feathers a "sub-adult?" I know why...

 Adult Cooper's Hawk
  Adult Cooper's Hawk
  Adult Cooper's Hawk
  Adult Cooper's Hawk
  Adult Cooper's Hawk
  Adult Sharp-shinned Hawk
   Adult Sharp-shinned Hawk
   Adult Red-tailed Hawk
   Adult Red-tailed Hawk

18 Comments:
Anonymous Derek Lyon said...

Okay ... I'll bite ...
Why is "sub-adult" often used for accipiters but not Red-tails.

Oh, and I agree that 'retained feathers' can't be seen on a live moving bird in the field. At a hawkwatch it's sometimes hard enough to just ID the species without worrying about a retained feather. Juvie or adult, done, case closed (Unless the bird is an eagle or Swainson's).

June 13, 2013 at 3:04 PM  
Anonymous Mia McPherson said...

Good question Jerry, I don't know though but I will check back to find out the answer.

June 13, 2013 at 5:35 PM  
Blogger Jerry Liguori said...

Hi Mia

That questiuon at the end was a bit facetious...

June 13, 2013 at 8:25 PM  
Blogger Vic Berardi said...

Great post Jerry and you defined it all very well, thanks!

That term "sub-adult" is so loosely used, and widely misused, it's almost annoying. I wonder sometimes why that is. Maybe it's just a cool thing to say, "I saw a sub-adult blah, blah blah . . ." I don't know. Your definition here explains it very well and in very simple terms, I love it! But back to the coolness thing for a moment, I do think "sub-adult" would make for a great vanity license plate :-)

Keep up the great work you do and sharing these tidbits with all of us!

June 14, 2013 at 6:49 PM  
Blogger Jerry Liguori said...

Thanks Vic, great comments.

It is a bit of an ego thing when people try to be superspecific with raptors, but the bigger issue is when they are incorrect and perpetuate a myth!

June 14, 2013 at 6:53 PM  
Anonymous Anonymous said...

The reason "sub-adult" has been used for accipiters is because it was published as such, but has not been published for Red-tails. Sometimes things are singled out but not treated equally when it pertains to other species in the identical way. Whether correct or incorrect.

June 16, 2013 at 7:19 PM  
Anonymous Anonymous said...

Man I love that second-to-last Cooper's hawk with wings on the down stroke. Those new flight feathers coming in under the old looks crazy!

Jamie C.

June 18, 2013 at 8:17 AM  
Blogger Jerry Liguori said...

Thanks for the compliment Jamie.

So glad you like my posts! Send me raptor pics if you want me to post them, or if you want to make a guest blog....

Lig

June 18, 2013 at 8:31 AM  
Anonymous Ian Maione said...

Jerry, how has slower development in eye coloration in females been established? I can only imagine it would have to be through observations of captive or falconry birds? I have observed local female Coopers hawks which have had more orange eye coloration than dark red - I've tended to assume this denotes a relatively young bird. One year the female had full adult chest plumage but lighter orange eye color. I anticipated she would develop darker coloration the next year, but she was replaced by a new (juvenile) female. Last year's breeding female was in full juvenile plumage with yellow eye color, but this year (I'm pretty sure it's the same bird again) her eye color has progressed to orange/red, but is still noticeably lighter than the male's.

June 22, 2013 at 7:28 PM  
Blogger Jerry Liguori said...

Hi Ian

Yes, captive birds have helped in this incident, included with nesting observations such as yours, and comparisons of many males and females (especially in their first adult plumage) in-hand at banding projects. It is neat that you have documented nesting birds and kept close tabs on them, it is a reliable way to learn certain things.

June 22, 2013 at 8:48 PM  
Anonymous Ian Maione said...

This is my breeding female - she is a pretty good example of an individual with fairly orange but not full red eye coloration:

http://www.flickr.com/photos/79774811@N00/9195615448/sizes/o/in/set-72157634333555960/

By contrast, here is a shot of her last summer (with the disclaimer that without bands I can't be 100% sure it's her again, but I think this is very probably). She had just started her molt and you can see the start of a few adult chest feathers coming through. However eye color is much yellower. She is also a good example of a breeding bird in juvenile plumage.

http://www.flickr.com/photos/79774811@N00/7627061230/sizes/h/in/set-72157630486983450/

July 2, 2013 at 5:53 PM  
Blogger Jerry Liguori said...

Ian

That is awesome! I love seeing birds and their progression from one year to the next....thanks for the links and thanks for checking out the site. Please keep checking in and adding to it.

July 2, 2013 at 6:08 PM  
Anonymous William Dove said...

There seems to be research that supports males having darker eye coloration than females in some accipiter species. Acquiring the darker coloration sooner and attaining a richer red. It is supposedly not a guarantee on gender, however.

William

July 5, 2013 at 7:16 PM  
Blogger Jerry Liguori said...

Yes, absolutely William.

Most males change quicker than females and typically get the very dark eyes. Females can get dark red eyes as well, but some never do. Thanks for your comments!

July 5, 2013 at 7:28 PM  
Anonymous Ian Maione said...

I recently found this Coopers nest cam - unfortunately the young are pretty close to fledging and they probably will be around for a few more days tops, but this is the first such view I have come across for Coopers.

http://www.livestream.com/coopershawkwebcam?utm_source=website-channelpage&utm_medium=related

July 17, 2013 at 2:42 PM  
Blogger Jerry Liguori said...

Ian

That is awesome! A big clutch too, thanks for sending this link.

July 18, 2013 at 6:04 AM  
Anonymous H.Gomaa said...

The third photo from the top is rather interesting. That particular bird seems to be sporting a full adult red eye but is clearly going through it's first year molt from juvenile to adult. You can easily see that in the tail - the two center feathers are the beautiful slate blue of the adult with the brilliant white terminal edge, while the rest are clearly still in brown, immature plumage coloration. I didn't think either of the sexes acquired that full red eye so quickly. Any opinions?

November 10, 2013 at 6:37 PM  
Blogger Jerry Liguori said...

Hi H. Gomaa

Send me your e-mail at jerrylig@hotmail.com and I'll share some more photos with you of different ages and eye colors...thanks for the interest in my blog

November 10, 2013 at 8:06 PM  

Post a Comment

Subscribe to Post Comments [Atom]

<< Back to Previous





Powered by Blogger

Subscribe to
Posts [Atom]