Taxonomy
As noted above, this species was formerly included in B. striata, which at that time was erroneously known as B. striatus. The Early Pleistocene B. validipes, whose fossil remains were discovered in Florida, might have been the ancestor of the Green Heron as the living species seems to replace the extinct relative in the fossil record.
Subspecies distinction is uncertain at best. The color variation between populations is less pronounced than between birds of the same population. Migratory populations are longer-winged than those resident year round, but this cannot be used to delimit subspecies as it is quite obviously is a consequence of differing habits and can be expected to undergo convergent evolution in unrelated populations of this species that just share the same habits. Thus, thorough molecular phylogenetic studies would be required to resolve the question of subspecies delimitation.
The following subspecies are commonly listed, though the validity of most of them is seriously disputed:
- Butorides virescens anthonyi
- Breeds in the USA west of the Rocky Mountains, south to northern Baja California Peninsula, Mexico. Some resident, most migrate to western Mexico in winter.
- Butorides virescens bahamensis
- Bahamas. Resident.
- Butorides virescens frazari
- Southern Baja California Peninsula, Mexico. Resident.
- Butorides virescens maculata – formerly maculatus
- Southernmost USA through Central America to central Panama, Caribbean. Resident.
- Butorides virescens virescens
- Breeds from southeastern Canada to central and southern USA east of the Rocky Mountains. Winters from southernmost USA to northern South America.
Much of the dispute hinges upon the distinctness of the Caribbean and Central American populations, the second taxon in this species to be described. To describe the two most extreme views, some authors assemble the bulk of the mainland population in the nominate subspecies but treat the parapatric populations as distinct subspecies, while others place all resident populations in maculata and all migratory ones in virescens.
Read more about this topic: Green Heron