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Frugivorous birds are important in the dispersal of many fleshy-fruited plant species, including invasive plants. Consequently, we investigated three native frugivorous avian species’ role in potential dispersal and germination success of the invasive American bramble (Rubus cuneifolius) in South Africa, particularly in terms of amount of fruit ingested, transit time, and their effects on seed germination. Three common species of frugivorous bird species were predicted to positively affect the spread of invasive R. cuneifolius. The bird species (speckled mousebirds Colius striatus, red-winged starlings Onychognathus morio and dark-capped bulbuls Pycnonotus tricolor) were fed R. cuneifolius fruit in captivity and amounts ingested were determined together with transit times. Seeds that were excreted and/or regurgitated by the three bird species, manually extracted seeds, and control whole fruit were then planted and their germination assessed daily. Although the three bird species varied in the amount of fruit consumed (~ 10–30 g), there was no significant difference in amount of R. cuneifolius fruit eaten per gram body mass among the species. Bird-ingested seeds emerged a mean 21–23 days after planting, while the seeds from the whole fruit took longer to emerge (mean 28 days). Germination of seeds ingested by the respective bird species was significantly higher (~ 60–75%) than seeds manually removed from fruits (~ 52%) or seeds in whole fruits (~ 7%). This suggests that removal of pulp and seed coat abrasion by the birds increased germination success. The three bird species all had R. cuneifolius seed transit times greater than 20 min, demonstrating their potential to disperse seeds a distance away from the parent plant. The results showed that the three bird species increased the germination success and suggests they are potentially important dispersers of the invasive R. cuneifolius.

Avian frugivores play a key role in seed dispersal of many plant species, including invasive alien plants. We assessed the effect of gut passage on the germination of selected invasive alien plant species in South Africa. Fruits of four fleshly-fruited invasive alien plant species: Solanum mauritianum, Cinnamomum camphora, Psidium guajava, and Morus alba, were fed to two species of indigenous turacos, Knysna (Tauraco corythaix) and purple-crested (Gallirex porphyreolophus) turacos, and to invasive rose-ringed parakeets (Psittacula krameri). Seed retention time was determined as this can influence both seed dispersal and germination success. Germination success of ingested seeds was compared with that of manually de-pulped seeds, as well as to seeds in whole fruit. The germination success of seeds of all the invasive plant species increased significantly after ingestion by both turaco species compared with seeds from whole fruits. Germination success of manually de-pulped seeds did not differ significantly from that of turaco ingested seeds. In contrast, seed passage through the digestive tract of rose-ringed parakeets significantly reduced germination success and viability of ingested invasive plant species. Our results suggest that Knysna and purple-crested turacos are legitimate seed dispersers of fleshy-fruited invasive plants, while rose-ringed parakeets are mainly seed predators. Although seed predation by rose-ringed parakeets negatively affects the reproductive success of these plants, it is unlikely that this will suppress the spread of these invasive alien plants in South Africa as they are already well established. Furthermore, they can facilitate dispersal by seed regurgitation and dropping uneaten fruits away from the parent plant. Similar trends could be expected for indigenous seeds that rose-ringed parakeets feed on and therefore these birds remain a negative influence within invaded ecosystems.