Abiotic Factors as Predictors of Distribution in Southern African Bulbuls

The closely related Black-eyed Bulbul (Pycnonotus barbatus), Red-eyed Bulbul (P.nigricans), and Cape Bulbul (P.capensis) occupy parapatric to locally sympatric ranges within southern Africa.We used a multivariate discriminant function analysis to relate the South African distribution of these species at the resolution of a quarter-degree square of latitude and longitude to a suite of six environmental variables extracted from digital models.The analysis correctly classified the distribution of these species for 89% of the 1,426 squares analyzed.Separation on the first discriminant function, which successfully characterized the distribution of P. nigricans, was mainly by the coefficient of variation in mean annual rainfall and mean July minimum temperature.Separation on the second discriminant function, which successfully characterized P. capensis, was mainly by the "normalized difference green vegetation index" (derived from NOAA satellite scans).Using the standardized coefficients for the first discriminant function, a model generated to predict the distribution of P. nigricans at a finer geographic resolution within our Eastern Cape Province study area was 93% successful.The results suggest that the three species occupy distinctly different habitats, as characterized by the suite of six environmental variables that we analyzed.