Below is a photo of four immatures which are perhaps representative of birds hailing from the Hudson Bay region. Note here how on all of these birds the pale supercilium is not sharply constricted above the eye, with pale areas ‘invading’ the supra (above) loral (lores; area between bill and eye). Immature White-crowned Sparrows are more difficult to place neatly to subspecies level but there are averages which are appreciable upon close study. If one were to make a case for Gambel’s (gambelii) with the immatures photographed, the following suite of characters would be present: a slightly shorter and less swollen bill with a more orangish cast throughout; lateral crown stripes averaging a lighter red; and a loral area which is (typically) entirely pale, lacking constriction in the supraloral region. The percentage of intermediate examples appears highest throughout the Hudson Bay region. This coincides with what James (1991) describes as an area of great introgression. 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 introgression of Gambel’s (gambelii) x Eastern (leucophrys) along the western coast of Hudson Bay. Regarding gene flow, this area is likely acting as a large geographic barrier toward further eastern influence of westerner, gambelii (Todd 1953).
Photo: A group of four immature Eastern (leucophrys) White-crowned Sparrows. Tapadero Sparrow Field, approximately 2.5 km ENE of the Goulbourn Sparrow Field. Full sparrow checklist here: http://ebird.org/ebird/canada/view/checklist/S31810133.
References
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