Friday, August 7, 2009
Warbler Guy, do you know why New World warblers are usually more colorful than Old World warblers?
(Townsend's Warbler, above)
Good question, Antoine (in Richmond, VA).
The answer is not obvious nor proven in scientific research.
My explanation relates to how birds evolved and new species became established throughout North America (i.e., a portion of the New World) over eons of time.
As a first step, think about the geographic spot or “epicenter” where our North America wood-warblers originated. That area is the Appalachian Mountain region that served as breeding areas to which tropical species of wood-warblers (such as the colorful Yellow and Black-Throated Green Warbler, to name just two of many species) began migrating and breeding within the distant past.
In turn, new, evolving wood-warbler species spread throughout North America as they colonized habitat when the glaciers melted within northern latitudes 12,000-18,000 years ago. Generation after generation of breeding isolation of these new, pioneering populations from one another allowed distinct appearances to flourish as new species.
So, for instance, “sister,” look-alike, colorful species such as the Black-Throated Green, Hermit, Townsend’s, Golden-Cheeked, and Black-Throated Gray Warbler are considered close first-cousin relatives – though all primarily breed in distinct geographical areas throughout North America that do not overlap.
In fact, experts consider these five warblers a “super species,” with the Black-Throated Green the initial precursor from which the other four look-alike species evolved and spread west and north throughout North America from their Appalachian origins.
As for the generally drab, uncolorful appearance of Old World warbler species (Sylviidae family) that primarily breed in Eurasia, their evolution occurred in a similar fashion to the aforementioned progression of our New World North American wood-warblers (the majority of which occur in the Parulidae family). That is to say, one or more drab, uncolorful original warbler species in the far past were the root species of the evolutionary tree from which other multiple species evolved and spread throughout Europe and Asia.
In short, it’s mere geographical luck that the USA’s location is within the latitudinal migration pathway that colorful neotropical/equatorial New World species chose as they evolved their migrational routes from the south in search of northern breeding territories.