Some claim that female budgies bite harder than males.
It is difficult to know the exact color of a budgie’s cere if the budgie is under eight months to one year old because ceres change colors until budgies are mature. If, however, you have a young budgie and its cere is brownish in color, you probably have a female budgie.
Male and female budgies can look alike unless you know what to look for when sexing them. One of the easiest ways to tell the difference between mature male and females budgies is to look at the cere. For budgies under eight months to a year in age, this technique might not be foolproof. Another way to determine the sex of your budgie is to notice its behavior with you and with other birds, if possible. You can also listen to the sounds your budgie makes to help determine if it is a male or female.
Look at your budgies' cere. The cere is where a nose would be, sitting just above the bird's beak. A male budgie's cere will be a bright bluish or purple color. Most of the time, their ceres will be larger than a female's cere. If you have an albino, dark-eyed clear, recessive pied, lacewing or fallow variety, the cere will be a brighter shade of violet or pink, according to the Budgie Place.
Female budgies will have less colorful and bright ceres. Most of the time, they will look white, tan or a dull pink color. A female's cere will also be rough in texture, looking like flaky or rough skin.
Watch your budgie. Male budgies are less aggressive than females and males are more outgoing than females. Males are more likely to seem friendlier and receptive to you while females are more temperamental and bossy. If you are watching a group of budgies interacting, notice which ones seem to be friendlier and which ones appear to be more aggressive with each other. Males are also more active overall and bob their heads while they are playing.
Listen to your budgie. Probably one of the easiest ways of knowing whether you have a male or female budgie is to listen to it. Males will sing more than females and females tend to make noises that sound angrier than anything that might be mistaken for a song. Males can sound mad at times, but not nearly as often as females do.