Geese are difficult to sex compared to poultry like ducks or chickens, which often display clear differences in plumage or physical characteristics. The lack of distinct sexual dimorphism in most goose breeds means visual identification is frequently unreliable until the birds reach maturity. For certainty, a combination of subtle physical cues, behavioral observation, and the anatomical method must be employed.
Observable Physical Differences
Males, known as ganders, often exhibit a slightly larger overall body size than females. Ganders can be 10 to 15% heavier and may have a more robust appearance with thicker, slightly longer necks. Their heads may also appear larger and more angular, contributing to a generally more imposing posture.
In breeds like Chinese or African geese, a fleshy bulge called a “knob” develops at the base of the bill, providing a more reliable visual indicator. The gander’s knob typically grows to be more prominent than the goose’s, particularly after the first year of life. This difference becomes more noticeable as the goose matures. However, many common European breeds, such as Toulouse or Embden, lack this pronounced head feature, making size and neck thickness the only differentiators.
Behavioral and Vocal Clues
Behavioral differences become more pronounced once geese reach sexual maturity. Ganders are generally more assertive and territorial, often positioning themselves between a perceived threat and the female or goslings to act as a protector. This defensive behavior can manifest as aggressive posturing, such as stretching the neck out low to the ground, hissing, or charging toward people or other animals.
Vocalization patterns also offer an observable clue, as the syrinx—the avian voice box—develops differently between the sexes. In many breeds, the gander’s honk tends to be higher-pitched, more shrill, or harsher, while the goose produces a lower, deeper, and sometimes softer honk. Individual variation can make interpreting the sound challenging. During the breeding season, the gander will frequently lead the goose in movement, and dominant, protective behavior strongly suggests a gander.
The Accurate Method of Vent Sexing
The most accurate method for sexing a goose involves a physical inspection of the cloaca, known as vent sexing. This invasive procedure is required because ganders possess a rudimentary phallus that is not externally visible under normal conditions. The female, conversely, has a small, often pointed, rosette of tissue called the genital eminence.
To perform the procedure, the bird must be securely held while the vent is gently manipulated and everted to expose the internal reproductive organs. In a gander, the phallus, which is often corkscrew-shaped, will uncurl and become visible when gentle pressure is applied around the vent. If the bird is a goose, only the soft tissue of the genital eminence will be present.
This technique is most reliably performed on sexually mature birds, as the male organ can be difficult to fully unsheathe in younger individuals. Only experienced handlers or veterinarians should attempt vent sexing. Improper technique carries a significant risk of causing internal injury to the bird, including damage to the phallus or other organs.