Twelve species of keratin decomposers isolated from 923 samples of feathers, nests and pellets of 90 species of free-living birds were clustered in 4 "econs" (numerical ecological groups): (A) Artroderma tuberculatum, A. ciferrii, A. multifidum, A. cuniculi (associated with the birds nesting in hollows); (B) Ctenomyces serratus, Arthroderma quadrifidum, Chrysosporium evolceanui (moderately alkalophilic species associated with the birds having a frequent contact with the soil); (C) Chrysosporium keratinophilum, Aphanoascus fulvescens, Chrysosporium tropicum (alkalophilic and hygrophilic species); (D) Arthroderma curreyi, Aphanoascus terreus (the species common in water habitats and associated frequently with exoanthropic birds). Two simple numerical procedures were used and compared: (1) Jaccard's association coefficient, and Sörensen's complete linkage clustering; (2) Forbes's association coeficient adjusted with chi-square, and the 3-linkage clustering technique. The method (2) seemed to be more effective.