Appearance: sexual dimorphism throughout year Breeding males have green crested heads highlighted with...

Appearance: heavy bodies, short black legs, long S-shaped neck, flat orange beak with bulging black knob...

Appearance: black head with white cheeks, black beak, black s-shaped neck that straightens in flight,...

Appearance: small goose, black head and neck, black beak and eyes, brown wings with black tips, white...

  Appearance: owl-like face; long, rounded tail with white band; small, sharply hooked beak; yellow...

Appearance: sexual dimorphism during breeding season, male looks like female during winter: gray-brown...