Seed dispersal of the Chinese tallow tree (Sapium sebiferum (L.) Roxb.) bybirds in coastal South Carolina

We used seed traps (n = 119) to quantify seed dispersal of the Chinese tall ow tree (Sapium sebiferum (L.) Roxb.) by birds in South Carolina during the October 1995 to April 1996 fruiting season. We tested if crop size, habita t type (spoil area vs. forest) and vee distribution (isolated vs. clustered ) affected the dispersal efficiency and number of seeds dispersed from tall ow 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 sam ple units (1570 m(2); n = 32), birds removed an estimated 675,000 +/- 56,00 0 of 1,681,000 +/- 113,000 seeds, about 40% of the total seed crop. There w as a vend 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. T he most productive unit was the only one to have a persistent seed crop. Th ese findings show that birds in coastal South Carolina use the tallow tree heavily as a food resource and are not generally saturated by present level s of tallow tree seed availability. Fourteen bird species consumed a total of 476 tallow tree seeds. The mean number of seeds probed, dropped, swallow ed and taken away in a beak were significantly different among bird species , as was the mean number of individuals per observation. Species differed i n the estimated numbers of seeds consumed per visit and total seed consumpt ion for the entire fruiting season. Important seed consumers included the n orthern flicker, American robin, boat-tailed grackle, gray catbird and the northern mockingbird. Red-winged blackbirds and boat-tailed grackles were s pecies that dropped many seeds. Heavy use and effective seed dispersal by d ifferent birds have contributed to the invasion success of the Chinese tall ow tree in coastal South Carolina.