The Fox Sparrow breeds in Boreal and mountain habitats throughout the north and the West. In winter, they migrate south or to lower elevations and are then found throughout the North American continent and into northernmost Mexico. This is a highly geographically variable species, and it has been suggested that it is best to separate it into various species level units. There is a northern form, the only one that is obviously reddish (and therefore “fox colored”) which is found from Alaska to Newfoundland as a breeder; this is also the most extensively migratory form and it may be known as the Red Fox Sparrow. The other three forms are in the West. One that breeds throughout the Rocky Mountains is grayish above with a rusty tail and a standard sized bill, it is the Slate-colored Fox Sparrow. Farther south and west in the Cascades – Sierra of Oregon and California is a similar looking bird but with an oversized bill. This is the Thick-billed Fox Sparrow. Finally in coastal Alaska south to the Pacific Northwest is a very dark and overall brownish form, the Sooty Fox Sparrow. Apart from visual differences, there are marked differences in vocalizations and molecular data that suggest that the various forms are distinct entities. However, the molecular data (and morphology of some birds) does suggest that hybridization between forms does occur here and there. The jury is still out, and whether one considers this a single and variable species or four separate species is to some extent a philosophical one.