Date: 5/4/18 7:13 pm From: Ted Floyd <tedfloyd57...> Subject: [cobirds] Let's document Myrtle x Audubon's Warblers in Colorado
Hey, all. Earlier this Friday evening, May 4, I saw a couple of Myrtle x Audubon's Warblers at the University of Colorado South Campus near Tantra Road, Boulder County. Which got me to thinking about something...
Away from the breeding grounds, Myrtle and Audubon's Warblers co-occur across a huge swath of western North America, easily a million square miles. Yet *The Sibley Guide* informs us that hybrids are rarely detected away from the breeding grounds. I have no reason to doubt the overall accuracy of that statement, but I also note that, at least here in eastern Boulder County, hybrids (or intergrades, if you prefer) are legion.
Here's the deal. Even though Myrtles and Audubon's spread out across a vast region when they're not breeding, that's not necessarily the case for their hybrids. By analogy, consider the enormous winter range of the Dark-eyed Junco vs. the quite limited range in winter of White-winged Junco. (White-winged Junco in winter occurs chiefly in the ponderosa pine belt of the Colorado Front Range.) I wonder if Myrtle x Audubon's hybrids are similarly range-restricted. For what it's worth, I never knowingly saw a Myrtle x Audubon's hybrid in all my years of looking at Myrtle and Audubon's warblers in New Mexico (1992-1994) and Nevada (1999-2002).
It would be cool if we could say with some precision where Myrtle x Audubon's warblers go when they're off the breeding grounds. Definitely here in eastern Boulder County! But how much more extensively?
Here's a photo of one of the hybrids I saw this evening: