 Rodrigues solitaires grew to the size of swans , and demonstrated pronounced sexual dimorphism . Males were much larger than females and measured up to 90 centimetres ( 35 inches ) in length and 28 kilograms ( 62 pounds ) in weight , contrasting with 70 centimetres ( 28 in ) and 17 kilograms ( 37 lb ) for females . Its plumage was grey and brown ; the female was paler than the male . It had a black band at the base of its slightly hooked beak , and its neck and legs were long . Both sexes were highly territorial , with large bony knobs on their wings that were used in combat . The Rodrigues solitaire laid a single egg , that was incubated in turn by both sexes . Gizzard stones helped digest its food , which included fruit and seeds . 
