ABSTRACT The Cape Parrot Poicephalus robustus and the Grey‐headed Parrot P. fuscicollis suahelicus have recently been recognized as separate species, each with unique habitat requirements; the former a forest species endemic to South Africa, and the latter a woodland and savannah species with a wider distribution in Africa. We tested the hypothesis that stable isotope ratios can be used to identify dietary partitioning in the diet of these two species. We analysed carbon, nitrogen and hydrogen stable isotopes in feathers (three feathers each from seven individuals and one feather from five individuals) from these species at three sites along a north–south gradient; two sites c. 90 km apart where the two species each occur, and a site c. 685 km further south where the Cape Parrot occurs. Carbon and nitrogen isotope values of feathers were similar for the two geographically separated Cape Parrot populations, which were significantly different to values for Grey‐headed Parrot. Low variation within individuals, within each population, and within species reflected unique biome associations for each species. Hydrogen isotope values, on the other hand, reflected location along a north–south hydrogen isotope gradient. Our results support the hypothesis that stable light isotopes are a valuable tool in providing insight into the specialist and biome associated diets of two closely related parrot species.
Symes et al. (Mon,) studied this question.