'Endangered' in relation to a particular migratory species means that the migratory species is in danger of extinction throughout all or a significant portion of its range (Source: CMS Art. 1e) and clarified in Res. 5.3. as meaning 'facing a very high risk of extinction in the wild in the near future' (in order to achieve maximum compability with IUCN Categories of threat)

Animals, birds, fish, plants or other living organisms threatened with extinction by natural or human-induced changes in their environment. (Source: GEMET/TOE/KOREN) [...] unless steps are taken to change the cause of threat and decline. (Source: GEMET/BRACK)

A taxon is Endangered when the best available evidence indicates that it meets any of the criteria [A to E] for Endangered, and it is therefore considered to be facing a very high risk of extinction in the wild.(Source: IUCN RED LIST criteria, 2001)