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The Yellow-crowned Amazon (Amazona ochrocephala) complex includes several forms that are regarded as subspecies by some authorities and as full species by others. Juniper and Parr (1998) recognized three distinct species: the Yellow-crowned Amazon (A. ochrocephala), the Yellow-headed Amazon (A. oratrix), and the Yellow-naped Amazon (A. auropalliata). However, they noted that the status of these taxa was unresolved and that, for example, the presence of forms intermediate between the Yellow-headed Amazon and Yellow-naped Amazon suggests that they might better be treated as belonging to a single species. They also pointed out that clarifying the situation is made more complex by possibly age-related plumage variation and substantial individual variation within currently recognized subspecies. Although Juniper and Parr provisionally recognized three distinct species, for similar reasons Collar (1997) and others have provisionally treated the various forms as members of a single highly variable species. Subsequent molecular phylogenetic studies have revealed even more taxonomic complexity. Investigations by Eberhard and Bermingham (2004) and Russello and Amato (2004) indicated that the Blue-fronted Amazon (A. aestiva) may in fact be nested within the Yellow-Crowned complex (Russello and Amato concluded that the Yellow-shouldered Amazon, A. barbadensis, also falls within this group). Further sampling and analysis by Ribas et al. (2007) provided additional evidence indicating that actual evolutionary relationships among genetic lineages in this group may not be well reflected by the plumage variations by which the traditional taxa are defined (see below). (Ribas et al. and references therein should be consulted for more details.)
As traditionally defined, "Yellow-crowned Amazons" are mainly green with yellow feathers on the forehead and forecrown, sometimes extending onto the lores (the area between the bill and the eyes) and around the eyes. and often with a red spot at the base of the upper mandible (birds in the western Amazon basin have a green forehead). "Yellow-headed Amazons" are similar in appearance but have yellow extending over the entire head (immatures are largely green with little or no yellow on the head and little or no red and yellow on the wing). "Yellow-naped Amazons" have yellow limited to the nape and, sometimes, the forehead and forecrown.
Yellow-crowned Amazons move quietly in the treetops and fly well above the canopy with rapid, shallow wingbeats. They are found in tropical deciduous woodland, tall thorn scrub, humid gallery forest, seasonally flooded forest and secondary riverine growth, mangroves, pine savanna, Maurita palm stands in wetter open areas, cultivated land with remnant groves of trees, and even some suburban areas. They occur mostly in lowlands below 500 m. Nests are in tree cavities at 6 to 15 m. The "Yellow-headed Amazon" is endangered, although some of the other forms are locally quite common (e.g., "Yellow-crowned Amazon" in parts of Peru and Brazil).
"Yellow-headed Amazons" are confined to Middle America in Mexico, Belize, extreme eastern Guatemala, and extreme northwestern Honduras. Feral populations are established in Miami (Florida, U.S.A.) and Puerto Rico. These birds are local and uncommon throughout most of their range, with populations severely depleted by habitat loss and trapping for the pet trade both within and outside the native range. "Yellow-naped Amazons" occur in Middle America in the eastern Pacific lowlands of Mexico, Guatemala (possibly), El Salvador (lower arid tropical zone), Honduras, and Nicaragua to northwestern Costa Rica (from the southern end of the Gulf of Nicoya northward). The "Yellow-crowned Amazon" is found in Panama (and possibly Honduras) in Middle America and in South America south to eastern Brazil and northern Bolivia (it is rare in Trinidad).
(Collar 1997 and references therein; Juniper and Parr 1998 and references therein)