Instructions
Compare the bird in question to a few females from the flock or to the female you would like it to bond with. Males are generally 3 to 6 inches taller than females of their species. It may be difficult to use this method if the bird is not yet fully grown.
Observe how the bird interacts with you and with other geese. A male will usually hiss and flap his wings when you approach, while a female will generally be less disturbed. A gander will also attempt to protect any females that may roam from the flock and sometimes herd them back into the flock, while a female may actually try to go off by herself if she is attempting to nest.
Examine the genital area of the goose in question, if you can. Hold the bird upside down, being careful to restrain the head and beak. Carefully separate the cloaca, the genital fold. A male will have a one-half-inch-long penis inside the fold, while a female will have a flat area.
Consult a veterinarian before attempting to introduce a new goose to your geese if you are still in doubt about the sex of the animal.
How to Tell a White Male Goose From a Female
Geese are very social animals that are happiest living in flocks or bonded pairs. It is possible for you to introduce a new adult female into a flock. It is also possible to encourage an adult male, known as a gander, and a female goose to form a bonded pair. It is, however, not advisable for you to introduce an adult male to another adult male's flock or pair, as males will attack any gander they were not raised with. There are several species of white geese throughout the world. In some species, it is easy to tell a goose from a gander by simply observing, but others require a closer examination.