Within-colony segregation of foraging areas: from patterns to processes

Abstract

Spatial segregation of foraging areas among conspecifics breeding in different colonies has been observed in several colonial vertebrates and is assumed to originate from competition and information use. Segregation between sub-groups of foraging animals from the same colony (hereafter sub-colonies) has comparatively received limited attention, even though it may have strong impacts on colony structure and individual fitness, and thus on population dynamics of colonial species. Here we (1) used empirical data on a colonial bird and (2) developed an Individual Based Model (IBM) to shed light on the processes driving small-scale spatial segregation of foraging areas. Through the IBM, we tested whether memory and competition alone, without social information use, could explain the observed patterns of spatial segregation. By GPS tracking breeding lesser kestrels (Falco naumanni), we found that foraging areas of individuals breeding in two distinct sub-colonies within a large colony were significantly spatially segregated. Individuals from the two sub-colonies showed different departure bearings and encountered different habitats but did not differ in any fitness- or dispersal-related trait. Yet, individuals from a same sub-colony did not seem to follow departing or returning individuals when leaving for a foraging trip. The IBM showed that such collective spatial segregation does not necessitate any social information use to emerge: personal information and memory may be sufficient to mechanistically explain intra-colony segregation of foraging areas. Our results do not question the fact that colonies act as information centres, and that individuals may rely on social information for foraging. Instead, they suggest that within-colony spatial dynamics, arising from simple mechanisms not involving information sharing, might be widespread in colonial systems. While colonies have long been thought as single cohesive entities, we call for a careful generalisation of foraging data collected over a spatially limited part of colonies.