White-crowned Sparrows at Discovery Lake

Adult Gambel's White-crowned Sparrow. San Marcos, California. December 14, 2014. Greg Gillson.

White-crowned Sparrows show subtle but definite geographic differences across North America. Along the immediate West Coast (west of the Cascades and Sierra-Nevadas) there are three forms, or subspecies. The Nuttall's White-crowned Sparrow is a resident race along the central California coast. The Puget Sound White-crowned Sparrow breeds west of the Cascades from SW British Columbia to NW California, and winters south along the California coast. The Gambel's White-crowned Sparrow breeds in Alaska and across Arctic central Canada and Canadian Rocky Mountains, and winters furthest south, leapfrogging the other populations to winter from the central and western United States south well into mid-Mexico. This type of leapfrog migration is common in other species as well, where the northernmost breeding population is also the southernmost wintering form.

So here in San Diego, I have only seen the Gambel's form, October to April. Any other form would be rare here.

The 5 different recognized forms of White-crowned Sparrows across North America differ slightly in whether the black stripe continues through and in front of the eye, the dinginess of the underparts, the brightness of the back streaking, the color of the bill, and in song structure.

Five years ago I wrote about telling Puget Sound and Gambel's White-crowned Sparrows apart from an Oregon perspective.

Immature Gambel's White-crowned Sparrow. San Marcos, California. December 14, 2014. Greg Gillson.

Even the immature is identifiable to subspecies. The orangish bill, pale lores, and tricolor back (white, gray, brown) all indicate Gambel's, whether immature or adult.