Along with Horned Lark, Song Sparrow, Red-winged Blackbird, American Robin, and a few others species, Savannah Sparrow is one of the “cosmopolitan” North American species. It can be found literally from coast to coast, but, not surprisingly, there is a lot of complexity in their patterns of occurrence between those two shores!
Using the Clements taxonomy that eBird follows, Savannah Sparrow has no fewer than 21 subspecies which fall into up to six groups. Four of those have recently been proposed as species, and a fifth has been considered a species in the past. Three of these groups are real tough to pick out on this map: Belding’s Savannah Sparrow is restricted to Pacific saltmarshes, as is Large-billed Savannah Sparrow. Ipswich Savannah Sparrow breeds on one small island off Canada; but can be found along the length of the Atlantic Coast in coastal dunes. Despite the distinctive habitat of these taxa, we’d need to zoom in to finer scale to really have their patterns of occurrence show up (although the summer Salton Sea sightings refer to Large-billed Savannahs that return to “winter” there in June). However, within the widespread “Eastern” and “Western” groups, there are different breeding populations ranging from the Arctic to the prairies to desert grasslands and mountain meadows. Almost anywhere with knee-high grass, you can find Savannah Sparrows at some season.
This animation is fun to just sit back and watch at a distance. Watch the great grassland areas of the continent pop out in summer. See them stream south in fall, largely avoiding the high mountains of the Sierra Nevadas, Rockies, and Appalachians. Watch for differences in timing in the different regions. Simply enjoy the migration as it happens on the continental scale and reminisce about those big flocks of Savannahs that you kick up in your local grassland patch each fall, and where they might have come from.