Do larger frugivores move seeds further? Body size, seed dispersal distance, and a case study of a large, sedentary pigeon

Aim World-wide declines in large-bodied frugivores may change seed deposition patterns dramatically if body mass influences seed dispersal-related traits, such as dispersal distance. We quantified movement patterns and seed dispersal distances by Hemiphaga novaeseelandiae (kereru), the fifth-largest surviving pigeon world-wide. We then reviewed how body mass affects seed dispersal distance among fruit-eating birds globally. Location Taranaki and Canterbury, New Zealand. Methods We radio-tracked 24 kereru, following each bird continuously for up to 8.5 h, for a total of 43 tracking-days during the peak fruiting season (FebruaryApril). We estimated seed dispersal distances for three fleshy-fruited species using a mechanistic model based on kereru movements and seed retention times. We analysed global data for volant avian frugivores to determine the effect of body mass on time spent in fruiting trees, seed retention time, and dispersal distance. Results Kereru were highly sedentary, with an average of 32 +/- 39 (mean +/- SD) minutes and maximum of 315 minutes between flights. Kereru flew a mean of 77 +/- 159 m and maximum of 1457 m in a single flight. They dispersed 6687% of ingested seeds away from the parent plant. Mean seed dispersal distances for Beilschmiedia tawa, Vitex lucens and Pseudopanax arboreus were 95, 98 and 61 m, respectively, with all species dispersed up to 1469 m. For all three species, 7988% of seeds were dispersed < 100 m and < 1% were dispersed > 1 km from the parent plant. Globally, both the mean time spent in fruiting trees and seed retention time increased with increasing frugivore body mass. However, retention time increased faster, and therefore the dispersal distance and percentage of seeds moved away from the parent increased with body mass. Main conclusions Despite sedentary behaviour, kereru disperse many seeds away from the parent plant due to their even longer gut passage time, a function of their large size. Large-bodied frugivores are disproportionately important as dispersers not only because they can swallow larger fruits, but also because they are more likely to deposit seeds away from the parent plant and at greater distances.