Australian Lyre Bird

I have inherited a lot of stamps and am trying to look through them a few at a time basically to see if there are differences which may show that some are valuable. I have a jumbled mixed collection some from a serious collector and others from amateurs.
I have found 2 lyre birds stamps that look different re the shading on the left and have read that these could be valuable. Could someone give me some advice on this one please.

There are several threads about the lyre bird stamps already on this forum. Check this one out:

https://goscf.com/t/24480&whichpage=1