Tuesday, April 27, 2010
Warbler Guy, do all our returning eastern wood-warblers fly over the Gulf of Mexico during spring migration?
(Nashville Warbler, above. Note it’s often difficult to see its light brown-orange cap, though its prominent eye-ring and absence of wingbars are good field marks.)
“No,”(Byron in Laramie, WY) is the quick answer.
Although the majority of East Coast and Midwest breeding wood-warblers fly over the Gulf upon returning to the USA, there’s at least three that fly around the Gulf:
Nashville, Mourning, and Canada.
That is to say, these three “Circum-Gulf” migrating species use an overland route by arriving in the USA via Mexico.
The non-breeding season range of the Nashville Warbler is primarily in Mexico, so they have the least amount of miles to travel as migrators. Moving north in spring, they typically always arrive earlier than Mourning and Canada in northern Midwest and Eastern latitudes. In fact, among the 30 or so wood-warblers that birders observe annually in northern latitudes, Nashville may be considered an early arrival among the vanguard. Some of the Mexican wintering Nashville travel to the West Coast for breeding and are considered a different subspecies.
Canada and Mourning, on the other hand, are known as later arrivals in the warbler migration parade. Canada comes all the way from southern Central American and northern South America, so it makes sense that its route through Mexico takes longer than many other warbler species.
Patient birders often have to wait even longer into May to see Mourning. That’s because it winters almost exclusively in northern South America. Winging north requires Mourning to travel more miles than most arriving Nashville and Canada populations. As a result, Mourning usually doesn’t appear in its breeding territory until mid-May, often later in some spring seasons.
If, for example, cold weather occurs throughout much of May and northerly breezes prevail, then Mourning may not arrive until late May in portions of its northern nesting areas. Only Blackpoll is known to arrive later during these inclement seasons when many other warbler species may also arrive later than usual.