It's not always so easy to tell a bird's gender, as not all species lend themselves to easy gender determination. In those cases, the best thing to do is take your bird to an avian veterinarian to determine the gender.
One easy way for the vet to determine a bird's gender is to analyze the bird's DNA using a PCR-based test. This test identifies a bird's gender based on its chromosome pair (ZW in females and ZZ in males). This test is non-invasive, requiring nothing more than a drop of blood or some plucked feathers, and can be performed for any age bird [source: Therion International].
Here's a list of some species that have obvious enough gender differences to easily tell the male from the female without resorting to medical testing:
- Canaries Although these birds are famous as singers, the male canary is the major crooner, and often spontaneously bursts out in song. The female is more reserved and usually only warbles now and then.
- Cockatiels Female cockatiels are generally sweet and reserved, while the males do most of the chirping. They're also the ones who can more easily be taught to talk (although there's no guarantee...) [source: ASPCA Kids]. Another way to know if your cockatiel is male or female is by its color. While most kinds of cockatiels are monomorphic (having no distinguishing coloring between male and female), there are exceptions. For example, the check patches on the male grey cockatiel are brighter orange than on the female [source: Bird Channel].
- Parakeets and budgies The color of the cere, which is the bump just above the nose, differs between the genders. The adult male has a blue cere, while the adult female has a pinkish-brown cere. Note: this is only true for adult parakeets. Young parakeets have a blue cere regardless of their gender [source: Azula].
- Zebra finches The males are generally more colorful than the females, and are more prone to silly antics [source: ASPCA Kids].