NEW WORLD NINE-PRIMARIED BIRDS
The great majority of modern birds have 10 primaries in each wing,
although the outermost one is often reduced in size. One group of birds has
lost this outermost primary: a huge group of wood-warblers, sparrows,
tanagers, and blackbirds, almost restricted to the New World.
Molecular evidence confirms long-recognized morphological evidence that these
birds are another large monophyletic group in the Passeriformes. Some
authors think they are so closely related to each other that they constitute
only one family, but the current official check-list puts them in separate
families (Parulidae, Thraupidae, Emberizidae, and Icteridae).
Exactly which species belong in each of these four families has not always
been clear! For instance, recent molecular evidence suggests that the
two "tanagers" that nest in North Carolina (Summer Tanager and Scarlet
Tanager) are actually more closely related to other Cardinalidae than to the
hundreds of species of true tanagers in the American tropics (in
the family Tanagridae)!
This huge group of New World nine-primaried passeriforms (over 350 species in
North and Central America alone) has its counterpart in the Old World.
The family Muscicapidae, restricted to the Old World, and its close relatives
the Sylviidae (Old-World warblers) and Turdidae (thrushes) constitute an
assemblage comparable to the New World nine-primaried families. The
evolution of small seed- and insect-eating passeriforms followed parallel but
separate courses in the Old and New Worlds.
In each case, one particular group of each of these big assemblages managed to
colonize the other hemisphere, probably across the Bering land-bridge.
Thus our thrushes and bluebirds are a small set of the Old World assemblage.
Conversely, European and Asian "buntings" are a small set of the New
World assemblage (the New-World sparrows)!
The take-home lesson is that the Passeriformes evolved at least three major
radiations of small birds, each based on a separate continent or hemisphere:
the Australian (crow) assemblage, the Old-World assemblage, and the New-World
assemblage. Thus most of the passeriform birds in North Carolina are
not closely related to those in Europe, Asia, Africa, or Australia, but they
are to those in Brazil and Argentina!