17 December 2012

A Nomenclature Correction on Ageing Near-adult Birds

It's been brought to my attention that the usage of the term "4th cycle" may be a bit misleading. I often use 4th cycle for birds that are very close to being adults, but may show a few signs of immaturity. For instance, this American Herring looks mostly adult, less its pink bill with black subterminal markings that are a bit more defined than a winter adult. Also note the sparse black marks on the tail:

 
Milwaukee, WI. 02 December 2012.
 
Another example of what I would call a 4th cycle is this Thayer's with just a few specks on the uppertail and the black subterminal marks on the bill:
 
Lake County, IL. 16 December 2012.
Although these individuals may very well be in their 4th plumage cycle, there is no definite way to prove that without more evidence from banded individuals. How can I be sure this isnt' a very advanced 3rd cycle, or even a somewhat retarded 5th cycle? So, from this day forward, I've chosen to abandon the usage of "4th cycle" without inserting a disclaimer such as "possible 4th cycle". Alvaro Jaramillo first brought this to my attention and argued the term "near adult" is much more informative and less assuming - I agree!

I do feel, however, that we should continue ageing 1st, 2nd and 3rd cycle birds as such since we know so much more about what each generation of those feathers should look like, for the most part. I am tentatively choosing to label birds with marked tails, tertials and sub-adult like bills "3rd cycles". I will be happy to adjust the usage of this term if anyone can provide me with a 4th cycle+ example of a bird showing these features. Although there may be some guess-work involved here as well, it's a convenient system that we as field observers must have in order to communicate.

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