A Song for APRIL 20

Previous Day  List of Days  Next Day

Click the sonogram to hear and see the sound.

This sweet and rather delicate song is common in my neighborhood this time of year, as the wintering Yellow-rumped Warblers color-up and start rehearsing for their big show up in the northwoods. This an abundant species. Most winter in the U.S., and most of the eastern subspecies, called the Myrtle Warbler, nest in Canada, with spruce-fir forests in the eastern U.S. also used. Probably this singer is a Myrtle, but I can't say for sure because I didn't see him, and I don't think the western Audubon's and eastern Myrtle forms are separable by songs, which are varied and plastic. Myrtles are also documented to copy Nashville Warbler songs, and I think Audubon's does it to.

Males of the two forms are easily distinguished in the field, and the females are not too difficult, but the taxonomy of their lineage is nontheless vexed, or maybe hexed. Back in the day when hybridization was considered a no-no for good species, the two forms, then considered separate species, were lumped into the Yellow-rumped Warbler. That became the status quo, but a flurry of "molecular phylogenetic" research (think of it as the ancestry.com of the bird world) in recent years has given us the following delicious dynastic scenario: First there was one species, then what is now Goldman's Warbler, in Guatemala, became isolated geographically and thereby genetically distinct. Then the western mountain population and the boreal forest populations were separated by glaciers, the eastern form becoming the Myrtle Warbler. Then these two populations rejoined and hybridized, creating Audubon's in the U.S. and Canadian mountains, while the ancestral western form remained in the mountains of Mexico. It is known as the Black-fronted Warbler. Experts on the situation consider the Myrtle sufficiently distinct to be a separate species, but it is not clear what to do with Audubon's, which grades into the Black-fronted and hybridizes with Myrtle in a narrow band where the boreal forest meets the Rocky Mountain forests. Should there be three species or four? Myrtle may not regain species status until more research is done on gene flow between Black-fronted and Audubon's populations. So, for now it's Yellow-rumped.

April 20, 2014 was a nice recording day in my front yard in Waggener Terrace. Go to the Ebird list to check out the other birds that were singing that morning.

Previous Day  List of Days  Next Day
Email: web at archmcallum.com