Peachfaced love birds are not sexually dimorphic. This means that there is no way to tell just by looking at them. There are 3 definite ways to tell the sex of a peachfaced love bird.
1) DNA-Sexing. There are many services online that will perform this for a fee, whether it's sending a toenail clipping or a plucked feather.
2) Surgical Sexing. Certain avian vets can do this, and they use a procedure called avian larynoscopy and they can tell you right away within minutes. They check to see if the bird has male or female organs.
3) Sex-linked mating. If the parents were sex-linked mating, then all females for example would look like the dad, and everything would be female. For example, a Green Opaline male x Normal Green female. All females will be green opalines, and all males will be normal green split to opaline.
Some people also use pelvic sexing, but it is not 100% accurate.
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