Abstract
Rapid rates of species range extension during the Holocene represent seed dispersal distances of at least 6 to 8 km per generation for North American species ofFagus, Quercus, andCarya, taxa whose fruits are heavy nuts. Occasional seed dispersal by biotic seed predators is necessary for these dispersal distances. One likely agent for dispersal across long distances and habitat discontinuities was the extinct (since 1914 A.D.) passenger pigeon (Ectopistes migratorius). This bird's abundance, capacity for delayed digestion, and nomadic habits strongly suggest an occasional seed dispersal role, although a coevolutionary seed dispersal relationship cannot be inferred from available evidence. The capacity of some heavy seeds for dispersal distances greater than those of most light, wind-dispersed seeds has biogeographic and genetic implications.