Dynamics of Warbler Assemblages during Migration

We investigated among- and within-year community-level patterns in the phenology of wood-warblers (Parulidae) in old field/deciduous forest habitat in western Pennsylvania. The numbers of each of 29 species of warblers captured in mist nets were summed over six-day intervals from January 1981 to December 1985, and the data for spring and fall periods were analyzed separately by detrended correspondence analysis (DCA). Despite substantial annual variation in species abundances, patterns and rates of species turnover were consistent across years. However, within-year patterns differed qualitatively between seasons; in fall, species turnover was unidirectional (species replaced each other in sequence), whereas in spring it was bi-directional (community composition in late spring came to resemble that earlier in the season). Timing of migration was also associated with the general regions in which species either bred or wintered. DCA proved to be a powerful tool for analysis of dynamic community patterns.