The dark patch on the chest area is common among Blue and Green IRNs especially males. The reason? I'm not sure but I think it is one of the effects of the genes that give each species their unique appearance. Currently, there is really no practical way for us to study those plumage modifier genes responsible in making birds look like its own species. It just seems like there is more dark pigmentation (melanin) deposited on the chest area. Somewhat similar to Cleartails on this photo:
On Zahir Rana's site "Psittacula World"
http://home.wanadoo.nl/psittaculaworld/ ... rameri.htm he describes Green and Blue IRNs' body plumage as:
"Body: General Green;
Greyish tinge on breast"
So even Zahir notices it like I do on several of my birds. On some, the greyish or darkish breast tinge is subtle and yet on others, it is more pronounced. Here are some more visuals....
Imran's male IRN on the right also shows a pronounced dark chest. The left male doesn't. So I suspect that some IRNs will carry the minor "dark chest" gene and some won't.
