An Eight-Year Study of Avian Seed Dispersal to an Artificial Water Source

I monitored seed deposition to an artificial water source (i.e., bird bath) for 8 years in suburban Georgia to provide insight into the fruiting phenology of bird-dispersed native and non-native plant species, determine seed-dispersal distances, and identify the most likely avian seed dispersers. I recorded 2807 seeds of 25 bird-dispersed plant species in the bath. Native plants (16 species) comprised 79.6% of all seeds, while non-native invasives (NNI; 8 species) and ornamentals (1 species) made up 14.6% and 5.9%, respectively. The frequency of overall seed deposition peaked in late summer (July–September), with a second peak in winter (January–February); seed number per month mirrored this pattern. Diversity and abundance of seeds from NNI plant species peaked in late winter, after the peak of native plant species, and NNI species were absent from August to October. Based on the distance to the nearest fruiting specimen of each species, birds likely dispersed seeds to the water source from within 25 m for 8 species, while the seeds of 17 species came from >25 m. Of the 33 bird species visiting the bird bath over 2 years, the likeliest seed dispersers were Sialia sialis (Eastern Bluebird) and Turdus migratorius (American Robin), followed by Sayornis phoebe (Eastern Phoebe), Setophaga coronata (Yellow-rumped Warbler), Toxostoma rufum (Brown Thrasher), and Mimus polyglottos (Northern Mockingbird). The use of artificial water sources as seed traps could be attractive due to the method's simplicity, low impact on birds, high yield, scalability, capacity for year-round study, and potential for understanding important aspects of avian seed dispersal, from fruiting phenology to forest restoration.