the way i was told (and it is descibed in the bird mags) is the other way round.
circular for hens , straight up and down for cocks ??
but anyway , it only works for some people. u have to have the 'gift' !
i have tried it several times and nothing moves !
i watched an old lady in a pet shop (she was the owner) do it over a canary many years ago and in my opinion she was making it move herself !
probably made more sales that way . if u wanted a cock she could swing it and if you wanted a hen she could rotate it ? lol