The main purpose of many protected areas (PAs) is the long-term preservation of biodiversity and ecosystems. In Europe, several PAs have been established to protect wetlands, which are a key habitat for biodiversity and ecosystem services, but have undergone dramatic destruction and degradation. Because of drainage, reclamation and conversion, many wetlands now occur as habitat remnants, and are often protected by PA networks. However, the effectiveness of such networks in conserving biodiversity had been rarely assessed.

In our, work, we have evaluated the effectiveness of a system of PAs comprising 26 small wetlands for the conservation of wetland birds over three decades. We investigated the changes in species’ occurrence in the period (1989–2019) within the wetlands of the network, and related it to the species’ degree of ecological specialization. 10 out of 23 species increased their occurrence rate, seven remained stable and six declined. The number of habitats that a species use was a predictor of the occurrence trend: species relying on one or a few habitats (i.e. specialized species) declined, whereas the generalists ones, i.e. those using a plurality of habitats, increased. Several species that are rather common in most of their European range increased, e.g. mallard Anas platyrhynchos, grey heron Ardea cinerea, coot Fulica atra and moorhen Gallinula chloropus. Less common species that also underwent an increase in their occurrence rate were black kite Milvus migrans and common sandpiper Actitis hypoleucos. The species with declining trend in occurrence rate were species with an unfavourable conservation status in Italy (two bad, three inadequate, one unkwnon). Even more relevant, they were mostly species with more specialized habitat requirements within the study region, such as water rail Rallus aquaticus, great reed warbler Acrocephalus arundinaceus and reed bunting Emberiza schoeniclus. Mute swan Cygnus olor appeared stable.