Fleshy-fruited plants are an important component of the invasive flora of the northeastern United States, but few studies have examined how avian frugivory may benefit such plants. European starlings (Sturnus vulgaris) are one of the most abundant avian frugivores in New England, and if effective seed dispersers for fleshy-fruited invasive plants, starlings may participate in a mutualistic interaction which benefits both the invasive plants and birds involved. Here, we investigate the role of European starlings in facilitating the germination of three invasive, fleshy-fruited plants with which they co-occur: Elaeagnus umbellata, Celastrus orbiculatus, and Rosa multiflora. For each plant species examined, less than 20% of the seeds ingested by captive starlings were not voided, and assumed to be destroyed as the result of passage through the digestive system. Starlings retained the seeds of E. umbellata 29 (mean) ± 19 (SD) min, C. orbiculatus 43 ± 20 min, and R. multiflora 27 ± 9 min. We also examined whether ingestion of seeds by starlings affected the germination of E. umbellata and C. orbiculatus seeds. Seeds that were cleaned by hand or regurgitated by birds had the same likelihood of germinating, and were significantly more likely to germinate than were seeds contained in intact fruit. Defecated C. orbiculatus seeds germinated significantly less well than hand-cleaned or regurgitated seeds, but better than those that were contained in intact fruits. We also found that C. orbiculatus seeds ingested by starlings required significantly less time to germinate than those contained in intact fruits. This study shows ingestion by starlings improves germination for both E. umbellata and C. orbiculatus seeds, and that starlings retain seeds long enough for seed dispersal to occur. Studies to determine the extent to which starlings feed on these plants, and the distances which seeds are moved, are needed.
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Vol. 136 • No. 3