amaulipas
(Goldman and Moore, 1945:354).

Migrant birds from the eastern flyway and less commonly migrants from
western North America pass through northeastern Coahuila. The following
breeding birds seem to be associated with this province: Harris' Hawk,
Bobwhite (_C. v. texanus_), Scaled Quail (_C. s. castanogastris_),
Yellow-billed Cuckoo, Groove-billed Ani, Green Kingfisher,
Golden-fronted Woodpecker, Hairy Woodpecker (_D. v. intermedius_),
Ladder-backed Woodpecker (_D. s. symplectus_), Vermilion Flycatcher
(_P. r. mexicanus_), Cave Swallow, Gray-breasted Martin, Black-crested
Titmouse (_P. a. atricristatus_), Carolina Wren, Long-billed Thrasher,
Curve-billed Thrasher (_T. c. oberholseri_), Blue-gray Gnatcatcher (_P.
c. caerulea_), Hutton's Vireo (_V. h. carolinae_), Bell's Vireo (_V. b.
medius_), Yellow-throated Vireo, Red-eyed Vireo, Summer Tanager (_P. r.
rubra_), Olive Sparrow, Cassin's Sparrow, and Black-throated Sparrow
(_A. b. bilineata_).

_The Sierra Madre Oriental Biotic Province._--Southeastern Coahuila is
in this province that includes mountains in southern Nuevo Leon,
southwestern Tamaulipas, and eastern San Luis Potosi. Areas classifiable
as Canadian, Transition, Upper Sonoran, and Lower Sonoran in life-zone
are found in this province. This region of Coahuila receives the
highest rainfall; this is evidenced by the luxuriant growth of boreal
plants living in the higher places there (Baker, 1956:131). Spruce,
pine, and aspen occur at higher elevations and oaks, thorny shrubs, and
grasslands are present lower down.

Birds of central or southern Mexico reach the southern part of
Coahuila; the Thick-billed Parrot, Hooded Yellowthroat, and
Rufous-capped Atlapetes are examples. A boreal forest on the higher
slopes of the mountains of southeastern Coahuila is suitable for
certain northern birds such as Goshawks, Pine Siskins, and Brown
Creepers. Some species of birds ordinarily associated with western
North America are present in Coahuila only in its southeastern part;
striking examples of disjunction in range thus occur. Probably sometime
in the past these birds were distributed throughout most of Coahuila.
When this area became arid, these species disappeared from all of
Coahuila except from the high mountains in the southeastern part. For
example, Steller's Jay and the Scrub Jay are absent in the Sierra del
Carmen of northwestern Coahuila but do occur in southeastern Coahuila.

Migrants of the eastern f