Once your bird is a few weeks old, you will be able to determine the sex by looking at its cere (the nose and nostril are). In normal circumstances, a hen’s is brown, and a cock’s is blue. During the mating season, the hen’s cere will become enlarged and scaly and the cock’s becomes a darker shade of blue. Simple!
Despite this basic rule, there can still be some complications. Sometimes a hen’s cere will be blue, this is because their breeding hormone levels are low. When birds are ill their cere will also be this light blue, or sometimes even just white with a slight hint of blue. Interestingly, in the wild a hen’s cere is light blue, only turning brown during the nesting season. In younger hens, the cere is a light blue with white around the nostrils.
Male birds, although nearly always rocking a blue cere, may have a brown or browny-pink cere if his breeding hormones dip below the norm, or if he is ill. An ill male may also develop a yellow-greenish tinge around the nostril area. In an immature cock, the cere is a blueish pink or light purple.
The clue is in the cere - a female's is brown, and a male's is blue
Some parakeets are harder to sex. Albino, Lutino and Mottled birds usually have off-white, light pink or blueish pink ceres, and males of some of the pied varieties have light pink, blueish pink or white ones. With there being so many variations of this little bird, there is always a chance that your parakeet will have an “ambiguous” cere color. However, in 90% of cases, the brown-or-blue rule will apply.
Despite all these complications, cere color is by far the easikest way to sex your bird. There are also a few gender-related differences in voice and behaviour too; but these are not as consistently “male or female” as cere color. If you do happen to inherit an adult bird of unknown sex with an ambiguous cere, pay special attention to bonding behavior - any excessive head-bobbing means your bird is likely to be a male, and nay excessive squawking, rather than chirruping and singing indicates that your bird is female.
Young Parakeet Sexes
Younger birds of all types are much harder to sex than adults. At around three weeks old, cocks develop a blueish-pink cere, sometimes verging on lilac, and females have a blueish-white one, usually with a hint of pink around the nostrils. If the young birds belong to the Albino and Lutino group, you will not be able to sex them without an internal examination - which is something you should never attempt in any circumstances. Time will deliver the answer, and there is no need to interfere with a still-developing bird.