Pullet or roo?
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Another thing works for me is using the secondary wing feathers.
I know these are older birds but it still works with young chicks.
Here's a Black Australorp pullet. Secondary wing feather stay together and there will be a gap between the secondary and primary feathers.
Here's a Black Australorp cockerel. Secondary feathers will spread out and there won't be a gap between the secondary and primary feathers.