Pigeons and Rainforest Trees in Tonga: Their Interdependence in Shrinking Forest Remnants

Abstract

Due to extensive prehistoric extinctions of other frugivores, Pacific pigeons are thought to be one of the most important seed dispersers of large-seeded plants in Tonga, yet virtually nothing is known about their interactions with their food plants. I examined their potential for dispersing large seeds by reviewing their known food plants in Tonga and recording defaecations, regurgitations, and movement patterns. Pacific pigeons consume the fruits of at least 38 tree species native to Tonga. The fruits of 25 species and the leaf of an unknown species were newly identified in this study. Most defaecations and all regurgitations contained a single seed of a single species (11% of defaecations contained 2 species) and were located beneath fruiting trees. Pigeons usually regurgitate seeds larger than 20 mm in diameter whilst smaller seeds (≤ 14 mm) were typically defaecated. Based on observed movement patterns and known retention times for Ducula a regurgitated seed could be moved up to 143 m and a defaecated seed 808 m by foraging birds; whilst a pigeon flying continuously could disperse seeds 7.5 km, and 42 km, respectively. Location of dispersed seeds found in this study indicates actual dispersal distances are usually much less than this however. Results from this study suggest Pacific pigeons are excellent potential seed dispersers of large-seeded plants.