Seed dispersal is a critical ecosystem process for maintaining the integrity, diversity and structure of ecosystems. Understanding disperser movement is a key part of the seed dispersal process for vertebrate-dispersed plants, however we often ignore how variation in movement might alter seed dispersal. Nevertheless, temporal variation in disperser distances will impact how far seeds of different species are dispersed throughout the year. This is particularly important in novel ecosystems where plants and their dispersers have not evolved together and a decoupling between plant phenology and long distance dispersal events may occur. Here we examine temporal variation in movement of the three key vertebrate dispersers on the island of Oahu, Hawaii; a location where all native frugivores have gone extinct. Our study species range in body size, gape size, diet preference, and density. We examined disperser movement by radio-tracking 30 individuals (220 observation periods) from October 2015 to December 2016. We examined how time of day, month, wet vs dry season, breeding vs. nonbreeding season, and species impact the distance an individual moved per hour.
Red-whiskered bulbuls (Pyconotus jocosus), the largest of our species, moved, on average, at a faster rate (306 m/hr) than Japanese white-eye (Zoeterops japonicas, 215 m/hr) and red-billed leiothrix (Leiothrix lutea, 212 m/hr). We used AICc model selection to determine if movement rate changed through time and found that the models containing species (AICc weight = 0.45) and species and breeding season (ΔAICc=1.6, AICc weight = 0.2) performed well. Red-whiskered bulbuls and red-billed leiothrix moved more during the breeding season (317 m/hr and 220 m/hr respectively) than the nonbreeding season (254 m/hr and 190 m/hr respectively), while Japanese white-eye moved more during the nonbreeding season (230 m/hr) than the breeding season (206 m/hr). Based on our results, plant species that fruit and are consumed by red-whiskered bulbuls during their breeding season (Feb-Aug), when birds are moving farther, will have the greatest dispersal potential, followed by plants that fruit and are consumed by Japanese white-eyes during the nonbreeding season (Aug-Jan). Plants that are consumed by red-billed leiothrix, are more dispersal limited during their nonbreeding season (Sep-Mar). Our work here indicates that understanding temporal variation and interspecific differences in disperser movement is critical for understanding the impact invasive dispersers have on native plant communities.