From August 1977 to July 1979 16 species of parrots were studied at the Nucleo Pioneiro Humboldt (100 19' S, 590 12' W), on the upper Aripuanã river, in state of the Mato Grosso, Brazil. Special attention was directed to mechanisms of resource-patitioning between species.
It was evident that different size and weight give access to different food-items. Referring to weight, the 16 species can be divided into four groups:
Feeding strategies are different within groups: Ara manilata is a pure specialist; Tuit huetii, Brotogeris chrysopterus, pionopsitta barrabandi, Ara severa and Ara ararauna are partial specialists and have relatively long and marrow beaks. With regard to beak proportion, Brotogeris chrysopterus is more specialized than Tuit huetii en the same group of weight.
Species of very similar morphology, such as Ara chloroptera and Ara macao or Pyrrhura rhodogaster and Pyrrhura picta differ in the way they way they use their habitat. Ana chloroptera is observed in the upper layers of forest, near the highest tree tops, more often than Ara macao, Pyrrhura rhodogaster visits dense forest and growth more frequently than Pyrrhura picta. Seasonal differences in abundance and different breeding seasons separate the two Amazona species. Amazona ochrocephala is more common and rears its youngs in the dry season, whereas Amazona farinosa is reproducing and getting commoner in the rainy season.
If differences of one single niche-dimension do not clearly separate the species, a separation will be possible by using a combination of various dimensions.
Plants which produce a great amount of food in a short period of time show a special phenomenon: in such food-plants intra- and interspecific aggression between parrots is suppressed, and it even is possible to observe intra- and interspecific attraction. In this way big groups composed of individuals of various species profit from the rich food supply which otherwise would be wasted to a grest extent. Paticularly P. menstruus and both species of Pyrrhura are "specialized" for such food-plants.