Spatial patterns in army ant foraging and migration: Eciton burchelli on Barro Colorado Island, Panama

Abstract

Eciton burchelli colonies alternate bouts of central place foraging with periods of migration according to a set rhythm. When these army ants forage from a central nest site they separate neigh-bouring raids by using a pattern similar to that used by many plants in spiral phyllotaxis. During the intervening periods of migration, raids and emigrations are orientated to lower the probability that the raid path will cross itself and also to separate the successive bouts of central place foraging. This orientation has been analysed by a series of alternative, analytical models which reveal that the navigation is achieved by each day's raid and emigration being constrained to take roughly the same compass bearing as these activities on the previous day. An E. burchelli colony transferred to the previously Eciton-free and prey rich Orchid Island, exhibited temporal and spatial foraging patterns insignificantly different to colonies on Barro Colorado Island. The predetermined foraging patterns of E. burchelli are abandoned only when colonies fail to emigrate on some days and subsequently migrate in a radically different direction. This behaviour may be due to colonies avoiding areas marked by others, and could account for the absence of observed intraspecific collisions. By avoiding their own earlier raid paths and those of conspecifics, colonies of E. burchelli increase the amount of new ground they encounter. © 1983 Springer-Verlag.