Hi All,

Janet suggested I send this reply I made to her off list might be 
helpful for others on the list so I am forwarding it:

Hi Janet,

I am not prepared for more than the cliff notes version of this. A 
family-by-family run down would take a lot of time.

First the terms themselves:
1. Juvenile. Generally this applies to birds post-fledging to early 
independence. The trouble is some birds hold a full coat of juvenal 
(note spelling) plumage well into their first winter (e.g. gulls and 
shorebirds [in the same order: Charadriiformes]). Long-held juvenal 
plumage is rare in passerines (although traces sometimes stick around on 
stray individuals) so its most typical of non-passerines such as 
waterbirds and raptors. These days, as birders become more 
molt-conscious, there is tendency to refer to birds with these long-term 
juvenal plumages as "juveniles" as distinct from "first-cycle" or 
"first-alternate", or "first-summer" whatever.

2. Immature. While this is not wrong, it's imprecise, since it only 
means a bird that is not sexually mature. The old Peterson guides leaned 
on this term to cover all of those nasty pre-adult plumages and age 
classes, and the usage stuck with many birders over the years. For birds 
with really long immaturity it's a handy catch-all, especially if you're 
unsure of plumage sequence and molt stage -- what do you call a 
five-year-old Wandering Albatross anyway besides fifth year or fourth 
cycle? You get the idea.

3. Subadult is a good term for a bird that's just short of full sexual 
maturity, e.g. a four-year old Bald Eagle or your Red-shoulder. It's 
kind of poor for a two-or-three -year-old gull.

Banders have their own terminology. They refer to birds as "HY" 
(hatch-year), "AHY" after hatch year or "SY" (second-year) if you can 
tell the age by plumage or other criteria, then "ASY" (after 
second-year) unless you can go further, then it goes on to "TY", "ATY", 
etc. I like to try to keep things clear in my posts by using reasonably 
current molt terminology (e.g. "first cycle" or "first basic" depending 
on how old fashioned I am feeling) or something easy to understand such 
as "one-year-old" or some such. I hope the above discussion seems helpful.

Take care,

Walter Ellison

23460 Clarissa Rd
Chestertown, MD 21620

410-778-9568

Observing Nature is like unwrapping a big pile of presents every time you take a walk.


Janet Millenson wrote:
> Based on its plumage, the Red-shouldered Hawk that's been hunting in our 
> yard lately isn't an adult; presumably it fledged in 2007. So how should I 
> describe this bird -- "juvenile"? "immature"? maybe even "subadult"? 
> Different references seem to use different terms for the same thing.
>
> Can anyone explain the precise meaning of these terms, and how they apply to 
> various families of birds? Thanks.
>
> Janet Millenson
> Potomac, MD (Montgomery County)
> 
> ----------------------------------------------------------------
> "Look at the birds!" -- Pascal the parrot
>
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