Breeding herons and egret have been monitored annually since 1972 throughout Northwestern Italy, over an area of 57,591 km2 with the greatest surface of rice cultivation in Europe (about 2,000 km2). The total number of heronries increased from 40 in 1972 to 130 in 2013, in pace with an increase in the number of nests that peaked in 2000 to 23 times the initial number for Grey Herons, 4 times for Little Egrets, and a similar increase for the other species. But since 2000, a decreasing trend has become evident. In order to check whether this decline could be due to a diminished availability of prey, in turn linked to the rapidly changing rice cultivation practices, we studied the following topics, and compared the 2013 results with those obtained by identical techniques in 1980, 1990, 1995 and 2000 on the same study areas. 1) Changes in chicks diet for each of the 7 breeding herons and egrets; a great diminution occurred in some staple prey that use mainly ricefields for reproduction (amphibians) and an increase in new prey of recent colonization (the invasive Procambarus clarkii). 2) Changes in the surfaces of rice with little or no submersion, studied using satellite imagery; compared to almost 100% submersion until 1990, and to 70% submersion around 2000, the surfaces of submerged ricefields in 2013 were reduced to <50% at any given time during the breeding season. 3) Foraging success of the adults in rice fields, and their density in agricultural versus seminatural foraging habitats. A modeling is under way of the influence of these changes in prey availability, of the climatic changes, and of other factors, on these declining heron populations.