EVENNESS OF ABUNDANCE IN BIRD COMMUNITIES

1. The evenness of abundance is a summary statistic describing the relative abundances of the species that comprise a community. Evenness of abundance is high when the different species have similar abundances. 2. Evenness of abundance in bird communities tends to vary with habitat type, with number of species, with average size of species, and to a lesser extent with variation in size of species. Communities in more complex habitats have more even abundance distributions, as do those with more species, with smaller species and with a greater variation in body mass. 3. When evenness of abundance within communities is calculated separately for different taxonomic groups of birds, some taxa typically have more even abundance distributions than others. Taxa in which the different species tend to have similar abundances are generally those which are species-rich or those with relatively low adult survival rates. 4. Competition is a potential explanation for the described patterns in evenness. Taxa and communities which have uneven abundance distributions tend to be those in which intra and inter-specific competition may be strongest.