Owing to extensive prehistoric extinctions of large frugivores, Pacific Pigeons (Ducula pacifica) are thought to be one of the most important seed dispersers of large-seeded plants in Tonga, yet little is known about their interactions with their food plants. We reviewed their known food plants and recorded defaecations, regurgitations, and movement patterns of this species over 11 months in Tonga. The fruit of at least 38 native plant species and the leaf buds of one species are eaten by Pacific Pigeons in Tonga. Most defaecations and all regurgitations contained a single seed of a single species. Pigeons usually regurgitated seeds larger than 20 mm in diameter whereas smaller seeds were typically defaecated. On the basis of observed movement patterns in Tonga and retention times for Ducula, most seeds are probably dispersed away from fruiting trees (85% of regurgitated seeds, 99% of defaecated seeds), but within 50 m of the crown. Distances of more than 100 km are theoretically possible for defaecated seeds, although pigeon behaviour is likely to limit this maximum. Results from this study suggest Pacific Pigeons are excellent seed dispersers in Tonga.