On the Methods of Resource Division in Grassland Bird Communities

The results of this study make possible the following generalizations. The members of avian communities resident in simple grassland habitats coexist by virtue of differences in habitat preferences and feeding behavior and in very tall vegetation by differences in feeding height. The sum of these ecological differences is constant for all communities. Using only two habitat indexes, vegetation height and its standard deviation, it is possible to predict (1) the number of species, (2) the differences in their feeding ecology, and (3) their relative habitat separation in the community which occupies this habitat. As these predictions are made for South American communities on the basis of the communities studied in North America, and as the predictions hold regardless of grazing or irrigation programs, it is suggested that these communities have a full quota of species which are optimally adapted to their current environment.