Seed Dispersal of the Chinese Tallow Tree (Sapium sebiferum (L.) Roxb.) by Birds in Coastal South Carolina

• Published in: The American midland naturalist Vol. 144; no. 1; pp. 202 - 215
• Main Authors: RENNE, IAN J, GAUTHREAUX, SIDNEY A, GRESHAM, CHARLES A
• Format: Journal Article
• Language: English
• Published: Notre Dame University of Notre Dame 01-07-2000; American Midland Naturalist
• Subjects: Animal behavior; Birds; Contents; Forest canopy; Forest ecology; Forest habitats; Forest trees; Fruits; Plants; Seed dispersal; Seeds; Tallow; Trees
• ISSN: 0003-0031; 1938-4238
• DOI: 10.1674/0003-0031(2000)144[0202:SDOTCT]2.0.CO;2

We used seed traps (n = 119) to quantify seed dispersal of the Chinese tallow tree (Sapium sebiferum (L.) Roxb.) by birds in South Carolina during the October 1995 to April 1996 fruiting season. We tested if crop size, habitat type (spoil area vs. forest) and tree distribution (isolated vs. clustered) affected the dispersal efficiency and number of seeds dispersed from tallow trees. Traps captured 55,275 seeds and 107,993 functional locules; birds removed 48.8% of the available seeds. After scaling for canopy area of sample units (1570 m2; n = 32), birds removed an estimated 675,000 ± 56,000 of 1,681,000 ± 113,000 seeds, about 40% of the total seed crop. There was a trend for forest units to have greater dispersal efficiency than spoil area units but isolated and clustered trees were similar. Crop size was not a significant predictor of dispersal efficiency in either habitat but was an excellent predictor of the number of seeds dispersed in both habitats. The most productive unit was the only one to have a persistent seed crop. These findings show that birds in coastal South Carolina use the tallow tree heavily as a food resource and are not generally saturated by present levels of tallow tree seed availability. Fourteen bird species consumed a total of 476 tallow tree seeds. The mean number of seeds probed, dropped, swallowed and taken away in a beak were significantly different among bird species, as was the mean number of individuals per observation. Species differed in the estimated numbers of seeds consumed per visit and total seed consumption for the entire fruiting season. Important seed consumers included the northern flicker, American robin, boat-tailed grackle, gray catbird and the northern mockingbird. Red-winged blackbirds and boat-tailed grackles were species that dropped many seeds. Heavy use and effective seed dispersal by different birds have contributed to the invasion success of the Chinese tallow tree in coastal South Carolina.