eedom and can expand their niches in the absence
of related types of similar ecologic scope. For example, Miller
(1955a:158-159) reported that Hairy Woodpeckers occurred only casually
in the Sierra del Carmen and that the Ladder-backed Woodpecker has
spread out and seems to occupy the niche or niches usually characteristic
of the Hairy Woodpecker. Changes usually thought of as of subspecific
character seem to be taking place between the Ladder-backed Woodpeckers
of the Sierra del Carmen and of other areas, possibly because the
Ladder-backed Woodpecker in the Sierra del Carmen is extending its
ecologic sphere more than in areas where the Hairy Woodpecker exists.
Restriction in dispersal due to geographic isolation has probably
hindered gene flow, thus allowing rapid local adaptation, recognizable
in variation at the infraspecific level. Miller (_loc. cit._) listed
other birds that have expanded their ecologic scope; his work should be
referred to for further details.

The following birds are associated with this province: Black Vulture,
Scaled Quail (_C. s. pallida_), Turkey, Elf Owl, Green Kingfisher,
Hairy Woodpecker (_D. v. icastus_), Ladder-backed Woodpecker (_D. s.
cactophilus_), Wied's Crested Flycatcher, Buff-breasted Flycatcher,
Vermilion Flycatcher (_P. r. flammeus_), Black-crested Titmouse (_P. a.
dysleptus_), Cactus Wren (_C. b. couesi_), Curve-billed Thrasher (_T.
c. celsum_), Blue-gray Gnatcatcher (_P. c. amoenissima_), Hutton's
Vireo (_V. h. carolinae_), Summer Tanager (_P. r. cooperi_), and
Black-throated Sparrow (_A. b. opuntia_). Several kinds of birds, such
as the Band-tailed Pigeon, occur in the "pine islands" in this province
rather than on the desert floor.

There remain several kinds of birds that are not especially associated
with any one or two of the above-named provinces. These birds are
widely distributed and vary geographically without corresponding to the
Biotic Provinces. Examples of these species are: Black Phoebe (_S. n.
semiatra_ in northern Coahuila; _S. n. nigricans_ in southern Coahuila),
Violet-green Swallow (_T. t. lepida_ in northwestern Coahuila; _T. t.
thalassina_ in southeastern Coahuila), Black-eared Bushtit (_P. m.
lloydi_ in northern Coahuila; _P. m. iulus_ in southeastern Coahuila),
White-breasted Nuthatch (_S. c. nelsoni_ in northern Coahuila; _S. c.
mexicana_ in southern Coahuila), Brown-throated Wren (_T. b. cahooni_
in northern Coahuila; _T. b. compositus_ in southern Co