The avian seed dispersal system of eastern red cedar (Juniperus virginiana)

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Abstract
The avian dispersal system of red cedar, a low-quality, fleshy, cone-producing, woody plant, was investigated in southwest Virginia over a 2-year period. The red cedar cones ripened from late August through early October and persisted on the trees through May of the next year. Predispersal cone predation amounted to 0.9 and 3.1% of the total cone crop in 1980–1981 and 1981–1982, respectively. The proportion of the cone crop removed by avian dispersers was constant from year to year despite large differences in crop size. Active dispersal took place between November and March. Eight species of avian dispersers were identified. Single consistent feeders, such as the yellow-rumped warbler, accounted for slow, sustained removal of red cedar cones, whereas flock feeders, such as the cedar waxwing, European starling, and American robin, were responsible for rapid removal of entire cone crops. Bird-passed seeds showed 1.5–3.5 times greater total germination than manually depulped seeds. Average dispersal efficiency, defined as the proportion of the cone crop dispersed away (≥ 12 m) from the parent tree, was 68%. The high dispersal efficiency of red cedar may be explained in part by the short duration of visits paid by avian dispersers to cone-producing trees, the high mobility of these dispersers, and the relatively long transit times for ingested seeds. High efficiency combined with enhanced germination of ingested seeds may promote the rapid invasion of abandoned pastures by red cedar in the southeastern United States.