Visual Differences Between Male & Female Adults

[JLeigh]

My female guinea has a "humpback" close to her rump that the male doesn't have. Is this a male/female thing or just a genetic luck of the draw? It's very pronounced.

 

[PeepsCA]

That's referred to as the bustle, only the Hens develop it, so yah, it's a female thing. It's more pronounced during the laying season/warmer months, and especially noticeable right before she's going to lay her egg for the day.