Impact of invasive alien birds on seed germination

The invasive rose-ringed parakeet

The invasive rose-ringed parakeet (Psittacula krameri) (Photo credit: Niraj V. Mistry)

A recent study by C·I·B student, Vuyisile Thabethe and colleagues assessed how the germination of invasive seeds are influenced after being eaten by indigenous, Knysna (Tauraco corythaix) and purple-crested (Gallirex porphyreolophus) turacos, and invasive, rose-ringed parakeets (Psittacula krameri). To test this, fruits of four invasive alien plants: bugweed (Solanum mauritianum), camphor (Cinnamomum camphora), guava (Psidium guajava), and mulberry (Morus alba), were fed to the rose-ringed parakeets and turacos. The seeds from each birdís excreta or regurgitation were removed and planted in separate trays.

The indigenous purple-crested turaco

The indigenous purple-crested turaco (Gallirex porphyreolophus) (Photo credit: John del Rio)

Vuyisile found that seeds passing through the gut passage of the two indigenous birdsí had higher rates of germination. In contrast, seeds passing through the digestive tract of rose-ringed parakeets had lower rates of germination. The results suggest that turacos are seed dispersers of these fleshy-fruited invasive alien plants, while rose-ringed parakeets are seed predators. Damage to the seeds can be caused by the parakeets crushing them while feeding and/or destruction of viable seeds in the digestive tract.

“Although parakeets are not promoting the spread of invasive alien plants, indigenous plants may suffer similar fates and have reduced germination rates,” says Vuyisile Thabethe, lead author of the study. She adds, “This is perhaps one of the first studies highlighting the destructive behaviour of rose-ringed parakeets on indigenous fruiting plants in South Africa.”

The indigenous Kynsna turaco

The indigenous Kynsna turaco (Tauraco corythaix) (Photo credit: Sam Woods)

Read the paper:

Thabethe, V., Hart, L., Wilson, A-L., & Downs, C.T. 2015. Ingestion by an invasive parakeet species reduces germination success of invasive alien plants relative to ingestion by indigenous turaco species in South Africa. Biological Invasions DOI: 10.1007/s10530-105-0932-1

For more information, contact Vuyisile Thabethe at or Prof. C T Downs at