Censimento degli Ardeidi in Val Polcevera (Genova).

A census was carried out along the Polcevera and Verde Streams from December 2006 to December 2007 in order to examine the abundance of Ardeidae. Seven species have been observed: Grey Heron (Ardea cinerea), Little Egret (Egretta garzetta), Great White Egret (Casmerodius albus), Night Heron (Nycticorax nycticorax), Squacco Heron (Ardeola ralloides), Cattle Egret (Bubulcus ibis), Purple Heron (Ardea purpurea). The Grey Heron is constantly present in the area and it is the most abundant species; moreover it is the only one breeding in the area. The Little Egret is constantly present too, resulting rather frequent during the migrations, but less abundant in winter and summer. The Great White Egret is much less abundant and, differently from the previous species, it has been observed in the examined area only during the wintering period and sporadically during the spring migration. The other species of Ardeidae have been seldom observed, generally during the prenuptial migration. In addition to the census along the streams, the main Herons\u2019 roosting site in the Polcevera Valley has been monitored from December 2007 to May 2008. The data collected by this last method resulted useful since they have proved the effectiveness of the census along the streams for the Little Egret and the Great White Egret and they allow to assess the real abundance of the Cattle Egret, which can\u2019t be correctly counted by means of the census along the streams, because of the eco-ethology of this species