This one dropped into our yard for a couple of days, but seems to have moved on. They are an uncommon winter visitor and migrant in California. They are famous for negative assortative mating between the two color morphs. White-striped morphs prefer to mate with tan-striped morphs and vice versa. However, this species does not cleanly separate into tan and white striped morphs in the winter when there is more of a continuum of head stripe color variation, possibly to facilitate flock cohesiveness (Atkinson & Ralph 1980). This individual appears intermediate but may lose the slight tan color by Spring.
Reference:
Atkinson, C.T. & Ralph, C.J. (1980). Acquisition of plumage polymorphism in White-throated Sparrows. The Auk. 97: 245-252.
