Fluctuations in chick diet of the Squacco Heron Ardeola ralloides in southern France: changes over the last 30 years

Abstract

Capsule The composition varied between colony site, month and year. Aims To determine the diet composition of chicks and its variations in 2000 and 2001. To look for any changes over the last 30 years. Methods Chick regurgitates were analysed to determine which Order contributed most to the diet, by frequency and by biomass. Results During 2000 and 2001 chick diet was dominated by insects (92% and 70% by biomass, respectively), mainly Coleoptera (60% and 41%) and Orthoptera (27% in both years). The dry mass of Orthoptera, Coleoptera adults, Odonata and amphibians differed significantly between breeding sites, months and years.The proportion of invertebrates (in biomass) increased from 36.5% in 1970 and 31% in 1971 to 95% in 2000 and 90% in 2001 whereas the proportion of amphibians decreased in the same time from 49% and 33% in 1970 and 1971 to 5.0% and 9.5% in 2000 and 2001, respectively. Conclusion The proportion of prey types differed bewteen colony sites and months. Major changes were found in the diet composition between the early 1970s and 2000s. The possible hypotheses for the observed differences are discussed.