IUCN Red List classification of critically endangered species

Acipenser naccarii (Adriatic Sturgeon)
The Adriatic sturgeon is on the “critically endangered” list, and is indicated as being “possibly extinct,” as of a 2009 assessment (IUCN, 2017a). This is a species of sturgeon found exclusively in the Adriatic, both in fresh and sea waters. At its most robust, the species once had a range that extended as far south as Corfu, and as far inland along the Po River at its delta. It may even have been found in Spain, although evidence for this is inconclusive. The species was also located seasonally in the Venetian lagoon. There have been attempts to reintroduce the species to some areas, like Greece and also along the Po and other Italian rivers, but those efforts at population restoration have been unsuccessful. Since 1988, fish farming have successfully enabled the Adriatic sturgeon to spawn, but there is no evidence of wild spawning. The Adriatic sturgeon should be spawning in freshwater rivers.
The biggest threat to the Adriatic sturgeon is overfishing, and especially of catching the fish too young to reproduce. Another major threat has been the barriers to entry to its reproductive routes, such as dams along the Po River. This threat is being mitigated via the building of fish passages to allow the sturgeon to swim past the dams. The Allee effect, habitat competition, and water pollution are also threats.
Amazilia boucardi (Mangrove Hummingbird)
The mangrove hummingbird is described as being medium-sized for the species, and characterized by its green and bronze-green coloring. In fact, male and female have similar coloring with the female having more green spotting on the throat than the male, which has a turquoise-green throat. It is listed as being “endangered.” The mangrove hummingbird is endemic to Costa Rica, in a very narrow range of the Pacific coast “from the head of Golfo de Nicoya to Golfo Dulce,” (IUCN, 2017b). It has “patchy distribution” throughout the coastal mangrove areas, with current population estimates at about 2,150-4,150 mature individuals (IUCN, 2017b). Its preferred food source is the flower of the Pacific mangrove Pelliciera rhizophorae, but the species is not found in all areas along the coast with this type of mangrove. Also, the mangrove hummingbird has been spotted in adjacent areas that do not have this mangrove species. They nest between October and February.
The most significant threat to the mangrove hummingbird is habitat destruction, caused by human activities like the construction of commercial shrimp ponds and also logging for charcoal production, illegal cutting of the mangrove, dyke construction, and road construction. Pollution may also be a problem in some areas. Habitat loss may worsen as there have been trends towards increased real estate development along this coast. Sea level rises also threaten to reduce the habitat area for this species.
Amazona imperialis 
The imperial parrot, or imperial amazon, is a species of parrot endemic to the island of Dominica in the Caribbean. It is described as being “spectacular,” with purple and green coloring. In spite of moderately successful conservation efforts, the species is still listed as being “endangered,” partly because its habitat range is so small. It occurs primarily in the mountainous regions of the island such as Morne Diablotin. The preferred habitat of the imperial parrot is montane and elfin forest, where it nests in tree cavities and breeds during the dry season, between February and June. There are an estimated 250-350 individuals total, or 160-240 mature individuals. However, the parrot conceals the entryway of nest cavities, making it difficult to observe its nesting habits.
Primary threats to this species include habitat loss, especially as forest is cut down to make room for banana plantations. Hurricane damage and competition for nesting sites may also be a threat. Until the 1990s, people used to trap the bird for sale as pets or food, but this practice has been all but eliminated thanks to a successful public education program.











References

IUCN (2017a). Acipenser naccarii. http://www.iucnredlist.org/details/224/0
IUCN (2017b). Amazilia boucardi. http://www.iucnredlist.org/details/22687562/0
IUCN (2017c). Amazona imperialis. http://www.iucnredlist.org/details/22686411/0