Movement of Coconut Crabs, Birgus latro, in a Rainforest Habitat in Vanuatu

Abstract

Patterns of movement in the coconut crab, Birgus latro (L.), were studied using mark-recapture and radio-tracking techniques at a number of sites in the rainforest regions of eastern Santo, Republic of Vanuatu (South Pacific). Movement was assessed both for crabs caught and released in one place (indigenous) and for crabs caught and then released at a new location (introduced). Recapture rates in eastern Santo were very small ( < I%), whereas on the small islet sites (area <2 ha) the rate approached 20%. There were no significant relationships between distance moved and either time at liberty or size of the individuals for introduced crabs. But for indigenous crabs, size of individual was negatively correlated with distance moved. Recapture rates of introduced and indigenous crabs were similar , but introduced crabs moved significantly further from their point of release. Almost all radio-tagged crabs moved from their point of release; smaller crabs tended to move further. On eastern Santo, only two of five radio-tagged crabs were located again ; both had moved over 250-m away from their release point. On the islet sites, all radiotagged crabs were found again at least once; some of these returned to a number of different sites, indicating that B. latro seems to be able to home to particular locations. Nonetheless, dispersal of animals from an area, at least after handling, is a common feature.