Guess on if one of my Buff Orpingtons is a Roo!

[free range possum]

else am guessing but...I

This is incredibly interesting! I am now so excited to try it out on my own to confirm or not. I'm sure it takes an expert eye to get used to the method, but it would be so great if it works! I love helping people with the sex of birds and this would be awesome for a backup on tough ones to tell. Sometimes I just feel one is a cockerel based on what I thought was just facial bone structure, but maybe it was the eyes I was subtly picking up on all along!
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Maiden female birds haven't laid so their opening isn't bigger when feeling it.With pigeons, they are already small openings so it's pretty hard. Male birds do tend to look up with stretched necks. But the inner eye corners and fold (I'm guessing helps protect her as she turns eggs when old enough to brood) has been pretty consistent once I got this figured out.. Pigeons, sometimes get tired of brooding when it's hot, and a freindly pair of females will sometimes appear to be a couple but this has worked well. The differences are subtle till you catch on.. but The visible inner eye duct corners and slight fold have been consistent on females. It could be fun for you to explore that and hope it helps! Lots of pigeon people don't know this, but I like visiting with my birds and noticed this year's ago. Good luck and share!