Can the grey literature help us understand the decline and extinction of the Near Threatened Eurasian otter Lutra lutra in Latium, central Italy?

To trace the local extinction of the Eurasian otter Lutra lutra in Latium, central Italy, and examine the causes of the species' disappearance, we reviewed and classified information from both the scientific and grey literature according to the reliability and geographical accuracy of the records. The temporal and spatial patterns of 160 records from 23 geographical subunits from 1832 to 2006 suggest that the species collapsed between 1960 and 1975; two different extinction patterns were revealed by a set of multivariate analyses. In northern Latium the species collapsed because of several independent local threats. In central and southern Latium the species collapsed because of catastrophic habitat alteration (land reclamation during the 1930s) that negatively affected the source population. After this event the species went extinct in hilly and mountainous areas, where several population sinks occurred. We presume that this latter process drove the remnant otter subpopulations to extinction in central Italy, emphasizing the role of an extinction vortex in causing the collapse of this metapopulation rather than the classical threats recognized for this species. The value of the grey literature for a posteriori historical analysis of local extinction dynamics is highlighted by this research.