 More recently, it has been split into the present clade and the thick-billed fox sparrow.These have quite similar plumage, but can be readily distinguished according to mtDNA sequence and haplotype data (Zink 1994).However, these results were considered tentative (Rising & Beadle 1996) until more molecular data and apparent lack of wide-ranging hybridization coupled with ecological differences and adaptations led to confirmation of their distinctiveness (Zink & Kessen 1999); this group appears to be most closely related to the red fox sparrows (Zink & Weckstein 2003 "contra" Zink 1996), judging from biogeography.