Avian seasonality at a locality in the central Paraguayan Chaco

Abstract

Abundances of different species of birds were recorded in the central Paraguayan Chaco from August 1989 to August 1990 to investigate seasonal variation at the guild level. Species were grouped into guilds based upon primary diet or water dependence. The number of species (abundant : rare) in each guild is as follows: insectivores (21:35), granivores and folivores (20:6), faunivores (14:13), hydrophilic species (4:28), detritivores (3:1), nectarivores (1:1), and frugivores (0:5). Insectivores show the strongest seasonality (SD = 1.63) followed by hydrophilic species (SD = 1.43), nectarivore (SD = 1.41), faunivores (SD = 1.33), granivores and folivores (SD = 1.20), and detritivores (SD = 0.50). Chi-square tests indicated that differences between numbers of abundant versus rare insectivores (P < 0.01), granivores (P < 0.005), and hydrophilic species (P << 0.005) were highly significant. Results are interpreted in light of ecological and evolutionary processes.