Influence of Seed Processing by Frugivorous Birds on Germination Success of Three North American Shrubs

Abstract

Abstract Coevolutionary models of the interactions between fruiting plants and avian seed dispersers have been influenced by the assumption that regurgitation and defecation of seeds have diffferent effects on seed coats, and consequently seed germination. We evaluated how the manner of seed processing affects seed germination by feeding fruits of three bird-dispersed shrubs, spicebush (Lindera benzoin), chokecherry (Prunus virginiana), and arrowwood (Viburnum dentatum), to captive cedar waxwings (Bombycilla cedrorum) and thrushes (Turdus migratorius, Hylocichla mustelina, Catharus guttatus and C. minimus). Cedar waxwings defecate all seeds, whereas thrushes regurgitate most seeds. For all three shrub species and all five bird species, there were no differences in germination success between seeds manually cleaned of pulp, and cleaned, bird-passed seeds, regardless of whether seeds were regurgitated or defecated. However, seeds of Lindera and Prunus that were defecated by cedar waxwings and planted with f...