The foraging ecology and feeding behaviour of the grey heron (Ardea Cinerea) in the Camargue, S. France

Abstract

Foraging patterns of breeding Grey Herons were studied in the Camargue. Most individual birds used several different and widely dispersed feeding sites during the season. Some birds abandoned certain foraging sites but no seasonal trends were detected. There was evidence of both flock and territorial feeding at different sites. Birds were observed feeding in a number of different food patches (discrete feeding sites). There was evidence that the biomass intake rate influenced how long a bird would remain in a patch. When this was high, birds remained in patches, conversely when the rate was low birds left to feed elsewhere. Departures from a breeding colony to the feeding grounds were clumped. Birds leaving the colony together were likely to go to the same feeding site more often than birds leaving successively, but not together. I t is argued that the colony may have been used as an information centre. The diet of chicks in different colonies was compared. The proportions of the important prey types from different colonies and from different broods were different. There was evidence that adults sometimes pre-digest large prey so that their small chicks can consume prey that would normally be too large for them to eat. An experiment on prey selection provided evidence that chicks could select between two prey types which differed only in the irrelative profitability. The chicks consumed the most profitable prey type first. When the relative profit ability of the prey types was reversed, the chicks reversed their selection. This may be an adaption to maximise prey intake rate in the face of sibling competition. The results are discussed in relation to the success of the birds at different stages of their life cycle. The implications for the conservation of the species are considered.