Diets of Kauai’s invasive rose-ringed parakeet (Psittacula krameri): evidence of seed predation and dispersal in a human-altered landscape

Rose-ringed parakeets ( Psittacula krameri ) are the world’s most successful introduced parrots, and > 2000 individuals reside on Kauai, Hawaii. These birds destroy crops, but impacts to other native and non-native species are largely unknown. Our study objectives on Kauai were to determine: (1) diets of rose-ringed parakeets at five sites ( n = 9–25 per site), by sex, through crop and gizzard analysis and carbon and nitrogen stable isotope analysis, and (2) whether birds are dispersing or depredating seeds. We found 100% of birds ( n = 64) were eating plant material and 80% of their diet was seed; males had more food in their crops and gizzards than did females. Corn ( Zea mays ) was eaten by 67% of birds and averaged 31% of mass in crops and gizzards. Invasive yellow guava ( Psidium guajava ) was eaten by 97% of birds and averaged 30% of their diet. Parakeets are potentially dispersing yellow guava seeds, as 66% of birds had intact guava seeds, and each bird had an average of three intact seeds. Diets differed statistically among sites. Parakeets from Lihue Airport did not have any corn, and isotopic carbon values also supported low feeding on corn by birds at Lihue Airport. No seeds of native plants were identified in rose-ringed parakeet diets. Our findings of a diverse plant diet, frequent seed predation, and potential to disperse invasive species’ seeds implies that land managers in agricultural, urban, and natural areas should be concerned with the current expansion of these invasive birds on Kauai and elsewhere.