Low establishment success of alien non-passerine birds in a Central Italy wetland (Selva di Paliano: Latium)

The establishment success of exotic populations is typically analyzed as a binary response (success/failure), with the route taken by populations to their eventual outcome only rarely considered. This is especially true for wild populations, as well as for failed introductions. Therefore, we present a brief analysis of failed introductions of non-passerine bird species in a wetland of Central Italy. Only four species were able to reproduce independently from humans, but three of them went rapidly extinct because of poaching. The grey-headed swamphen Porphyrio p. poliocephalus, native to Western India and Pakistan, is the only species still present within the study area, despite the fact that it is in substantial decline. This high extinction rate may be due to (i) low propagule pressure, (ii) strict dependence on food supplied by man, (iii) poaching and (iv) lack of suitable nesting sites. Our study provides new evidence for the hypotheses that establishment success has been long overestimated, and that propagule pressure is a critical parameter in promoting the establishment of a non-native species in a new territory.