Food of the Little Egret Egretta garzetta and of the Great Egret Ardea alba in the Valle Canal Novo (Marano Lagoon, Udine, Italy)

Abstract

The pellets of the great egret Ardea alba and the little egret Egretta garzetta collected in the Marano Lagoon (Udine, Italy) have been studied during a two year period, 2002 and 2004. 654 pellets, collected monthly at the roosts, have been analysed to gather information about the diet of these birds. This study shows an abundant and almost constant presence of remains of invertebrates, expecially insects and other arthropods. Many of them have been identified up to generic, and sometimes to specific level with the help of materials preserved on the Museo di Storia Naturale di Trieste. The great egrets capture mainly micromammals and insects, but also fishes and Polichaeta, instead of the little egrets that feed with a great variety of prey, insects, fishes, Polychaeta, crustaceans, molluscs, arachnids and micromammals. Some pellets made just by macroinvertebrates testify that the great egrets like best these kind of prey, when they are plentiful. The larvae and the adults of big dragonflies, Notonecta and also ground insects, digger insects like Gryllotalpa and cicada’s larvae represent an important component of the diet of the little egrets and contribute also to the diet of the great egrets. The more consistent chitinous fragments were still in a good condition but, because of their resistance to digestive processes, we can suppose a capture by amphibians or fishes plundered in their turn by the birds studied. This study gives detailed informations about the number of the taxa of entomological and ichthiological interest and consequently about environmental diversity.