|Yellow-rumped Warbler (Myrtle), Dendroica coronata coronata, Click to Enlarge|
This male was of the "myrtle" sub-species. Some sources suggest that, like the red and yellow-shafted Northern Flickers, these sub-species were divided by the last North American glaciation. Those birds on the west of the glaciation became Audubon's warblers (or red-shafted Flickers) and those on the east became Myrtle's warblers (or yellow-shafted Flickers). Now that we are in a warming period these populations can hybridize and Calgary is close to the zone of hybridization, according to my copy of Peterson's Warblers. While this is probably fairly dry stuff to the non-biology geeks among you, I once heard someone (I fairly sure it was John Acorn but I could be mistaken), draw a wonderful analogy explaining how the distribution of species and genetic diversity illuminates the physical history of the planet. I think it's pretty amazing that this little bird can express not only the current health of our world but also its past as well.