A few living birds use their wings extensively as weapons. The steamer ducks of the South Atlantic are large, powerful birds with heavy, bright orange, horny knobs on the wings of both sexes. These are used by both sexes in display and fighting. Steamer ducks (especially males) fight a lot among themselves for mates and territory, and they often kill other species of water birds, holding them by the neck and beating them to death with the wing knobs. Some species of steamer duck are flightless; in other species, the males are often too massive to fly, even though juveniles and females can fly well. Selection has favored fighting ability over flying ability for many steamer ducks. Flight is perhaps less important for them than for many birds, because they live in shoreline habitats where food is plentiful all year round.

References:

Livezey, B. C., and P. S. Humphrey. 1985. Territoriality and interspecific aggression in steamer-ducks. Condor 87: 154157. PDF of this paper

Nuechterlein, G. L., and R. W. Storer. 1985. Aggressive behavior and interspecific killing by flying steamer-ducks in Argentina. Condor 87: 8791. PDF of this paper

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