A study of bird species diversity (BSD) on three seral stages characteristic of secondary succession on the New Jersey Piedmont was done during the winter of 1968—69, the spring of 1969, and the summer of 1969. The seral studies were a 2— to 33—year—old field (the herbaceous field), a 30—year—old field (the cedar field), and a climax oak—hickory forest (the oak forest). Two study plots, each with an area of 2 hectares, were chosen within each seral stage. Diversity indices were calculated using the Shannon—Weaver information formula, H'=—‐Σpilogepi. The species count (species richness) was found to account for many of the differences in BSD between the seral stages. The evenness with which species were numerically distributed (equitability) was found to be lowest and to be lowest and to have its greatest influence on the diversity index in the herbaceous field, due to the presence of large flocks of non—nesting species. Equitability was higher and more constant in the cedar field and oak forest. Territoriality was thought to account for the higher equitabilities observed in summer. In winter, the more rigorous environment was thought to be a factor in lowering the equitability at least in the cedar field.Equitability was not lowered as much in the oak forest, possibly due to aggregations of birds into mixed species flocks. The cedar field and oak forest were qui te different in the seasonal patterns of equitability. Both species richness and equitability were concluded to be important parameters in ecological study.