Warbler Ecology: Diversity, Similarity, and Seasonal Differences in Habitat Segregation

Abstract

Parnell (1969) gathered data on foliage type and habitat zone preferences of warbler species during spring migration and the immediate postmigratory period. Occurrences of species were recorded in four data sets: (i) foliage type, spring migration; (ii) foliage type, postmigration; (iii) habitat zone, spring migration; and (iv) habitat zone, postmigration. The present study is a re—analysis of Parnell's data by a number of statistical methods. The species that are most broadly distributed within the habitat have indices of ecological diversity (H) or niche breadth, of from 3 to 5 times greater than the most narrowly distributed forms. There is no correlation between H in foliage types and H in habitat zones within seasons, but there are significant correlations for H between spring migration and post—migration samples within vegetational subdivisions. Average H is not significantly different between seasons for either foliage type or habitat zone data. The dominant component of H is the number of vegetational subdivisions occupied, rather than the equitability of distribution within subdivisions. Ecological similarity (S = complements of average Euclidian distance in hyperspaces defined by vegetational subdivisions) among species is assessed by cluster analysis of each data set. S among species is not correlated between foliage type and habitat zone occurrences within seasons, but is correlated between spring migration and postmigration samples within vegetational subdivisions. Average ecological distance among species is greater in the reproductive season than during spring migration for both foliage type and habitat zone data. Increased segregation among species in the breeding season may be due to the reduction in the number of warbler species in the study area during that time, seasonal shifts in behavior as regards interaction of species, or simple population differences.