East of the Great Plains, an interesting variety of migrant White-crowned Sparrows can be observed. Some birds are “classic” examples of their respective subspecies; leucophrys to the east, gambelii to the west, but many migrants throughout this broad geographic area show intermediate characters.The percentage of intermediate examples begins to increase from the central tundra east to Hudson and James Bay (Banks 1964). This coincides with what James (1991) describes as an area of introgression between the western and eastern subspecies. East of the Rockies, gene flow throughout the trans-canadian population of White-crowned Sparrows appears largely fluid and unrestricted by geographic barriers, at least through to Hudson and James Bay. In his classic, detailed study, Banks (1964) determined that the proportion of dark-lored birds increased quite dramatically east of this area, suggesting there is a significant “disruption” to the apparent free-flowing introgression of gambelii & leucophrys along the western coast of Hudson Bay. Regarding gene flow, this area is likely acting as a substantial geographic barrier toward further eastern influence of westerner, gambelii (Todd 1953).
A fun & challenging winter project — I’ll have the full, very detailed post up by Spring 2016!
Figure 1: Two examples below are straightforward and “classic”, field guide-style representatives of their respective subspecies; four are not. Can you determine which is which? Photo Credits: (L to R; top to bottom): Nicole Richardson, Dan Ripplinger, Cog2012, Katie Fuller, John Picken, Marty Jones. Locations, L to R, top to bottom: New Liskeard, Ont; Missouri, USA; Iowa, USA; Long Point, Ont; Chicago, USA; Indiana, USA.
Note: this project is nowhere near possible without the aid of a great many excellent photographers. I am deeply indebted. Many thanks 🙂
Banks, R.C. 1964. Geographic variation in the White-crowned Sparrow Zonotrichia leucophrys. University of California Publications in Zoology 70:1-123.
James, R.D. 1991. Annotated Checklist of the Birds of Ontario. Second Edition. Life Sciences Miscellaneous Publications. Royal Ontario Museum, Toronto.
Todd, W.E.C. 1953. Further taxonomic notes on the White-crowned Sparrow. Auk 70: 370-372. https://sora.unm.edu/sites/default/files/journals/auk/v070n03/p0370-p0372.pdf