The Timberline Sparrow (Spizella breweri taverneri) is a taxonomically controversial American sparrow

American sparrow

American sparrows are a group of mainly New World passerine birds, forming part of the family Emberizidae. American sparrows are seed-eating birds with conical bills, brown or gray in color, and many species have distinctive head patterns....

. Usually treated as a subspecies

Subspecies

Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...

 of Brewer's Sparrow

Brewer's Sparrow

Brewer's Sparrow is a small, slim species of American sparrow in the family Emberizidae. This bird was named after the ornithologist Thomas Mayo Brewer.-Description and systematics:...

, it is still considered a distinct species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 Spizella taverneri by many authorities. While the Timberline Sparrow recognizably differs in some details, there is little reproductive isolation

Reproductive isolation

The mechanisms of reproductive isolation or hybridization barriers are a collection of mechanisms, behaviors and physiological processes that prevent the members of two different species that cross or mate from producing offspring, or which ensure that any offspring that may be produced is not...

 between the taxa.

When it was still considered a good species, it was listed as Least Concern by the IUCN.