Observations of unrelated but ecologically comparable species of sunbirds, Nectariniidae, derived from Malaysia, and honeyeaters, Meliphagidae, derived from Australia in the interstitial region of the eastern Indonesian Islands, indicate that these birds of identical size and similar food habits, are at least in partial competition. A study of the behavior of these birds in the territory of one of the species indicates an unequal numerical ratio between the species and dominant, aggressive behavior by the scarcer species (honeyeater). It is suggested that the behavioral activity of aggressiveness may in itsell serve to limit successful reproduction in addition to other phenomena such as clutch size or nesting success of which so far nothing is known. Any activities of a social or behavioral nature which may serve to limit the reproductive rate of the species may, therefore, have a considerable absolute survival value.