If you want to know whether your bird is a male or female, there are a few different ways to go about sexing. Considering that hormonal behaviors can cause issues it can be important to know how your bird will react to certain stimuli.
The first thing to determine is if your bird is dimorphic- in which males and females do not look the same. The above Eclectus parrots are probably the most striking example of sexual dimorphism. In most species it isn’t quite so pronounced. Budgie males have a blue cere, while females’ can range from white to tan to crusty brown. In cockatiels the male has a yellow head and the female does not. Indian ringneck males have a ring around their neck. Kakariki males are about 15 grams heavier than hens, have a stockier body, and wider beak. Even if a bird is dimorphic, if it is not the wild type color then sexing may be difficult. For instance, in cockatiels you can rarely sex lutino, albino, or pied birds visually. Lutino ringnecks can still be sexed, but pieds cannot. You need to know not only the species but the color mutation in order to accurately sex your bird.
If a bird cannot be visually sexed, or if it is too young (most need to molt into adult coloration before sexing can be done), then you need to use one of the methods below.
DNA sexing is easy and non-intrusive. Avian Biotech is the company I use. You can go on their website and ask for a testing kit. There are a few different methods: blood, eggshell, and feather. I prefer blood collection, as you can easily do it while grooming and it doesn’t involve plucking (yes, plucking!) 5-7 feathers.
All you need to do is restrain your bird as you would for grooming (see instructions here). Make sure you have Kwik Stop or flour on hand to stop the bleeding! When you clip a toenail, clip it a little further up than normal. You’re intentionally trying to clip the quick. When it starts to bleed, touch the nail to the circle on the blood card. You don’t need much. Mail it out, along with payment (currently about $25) and you’ll get your results back within a day or two after they receive the sample.
This method is usually requested by breeders who want to know the actual health of the gonads and other organs. The bird is briefly anesthetized, a small incision is made and a scope is inserted into the body to allow a veterinarian to observe the internal organs. After the bird is sexed, a tattoo is placed on the wing corresponding with the sex. Males are tattooed on the right and females on the left.
Sexing by behavior is not always accurate, especially if you are a pet owner with two birds of the same sex, in which case one may potentially exhibit more opposite sex characteristics. That said, I’ve found it very useful in sexing my own birds. Cockatiels and Indian ringnecks can usually be sexed long before they molt into their adult coloration. This is the Indian ringneck mating display. Both sexes demonstrate very specific body language and behaviors (in both videos the hen happens to be yellow). This is male cockatiel behavior. It takes experience though as you need to know what to look for in a particular species.