Head shape: Male geese tend to have a longer and more squared-off head shape, while female geese have a shorter and more rounded head shape.
Neck length: Male geese typically have a longer neck than female geese.
Colors: Male geese may have more vibrant and colorful plumage than female geese. This is especially true in the case of wing coverts, which are bright white in male geese and grayish in female geese.
Bill size: Male geese tend to have a larger and thicker bill than female geese.
Behavior: Male geese tend to be more aggressive and vocal than female geese. This is especially true during the mating season when male geese will defend their territory and mates.
DNA Test: If all else fails, a DNA test can be performed to definitively determine the sex of a goose.