canberrabirds

yet another unexpected visitor

To: <>
Subject: yet another unexpected visitor
From: "Philip Veerman" <>
Date: Mon, 1 Aug 2011 22:47:57 +1000
Do all males, when they reach (about) 4 years old, commence the process of changing to adult plumage (& beak colour), or are some left "permanently" in immature type colours? There are several examples of animals that do not fully achieve mature or reproductive status, because perhaps they don't have territory or social status.
 
Philip
 
-----Original Message-----
From: Geoffrey Dabb [
Sent: Monday, 1 August 2011 2:01 PM
To:
Subject: RE: [canberrabirds] yet another unexpected visitor

More important than what it is, for information purposes, is my suggested approach (put forward for discussion).

 

First, adopt a common terminology.  Are we going to use ‘juvenile’ for any pre-mature bird, or, as I suggest, reserve the term for true juvenile (first plumage) birds and use eg ‘ímmature’ for birds from second plumage and before maturity.

 

Secondly, get the most informative image.  Is the below the best available?

 

Thirdly, look for signs that the bird is a true juvenile (first plumage) bird.  The below is evidently not in that category.

 

Fourthly, examine the bill for signs of yellowing.  (Not entirely clear in the below.)

 

If the bill is entirely black, the bird could be a 2/3 year bird of either sex or a female between 2 years up to and including maturity.

 

If the bill has signs of yellowing it is a male from 4 years to short of maturity.

 

Information about relevant behaviour or help from someone with expertise on plumage differences might be able to advance the matter further.

 

By the way, I sent my earlier message to Danny Rogers who added the comment: 

 

I would incidentally be surprised if males were completely consistent in the age at which plumage and bare part changes occur - in other species of bird in which long delayed maturity occurs there usually turns out to be some variation - in part probably driven by social and territory status, but perhaps with lots of other interacting causes too.”

 

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