tag="{http://www.w3.org/1999/xhtml}a">[A] Specimens in worn breeding plumage.

Measurements of our five adults from the barrier island are presented in Table 3 for comparison with those of C. s. semipalmatus and C. s. inornatus given by Ridgway (1919:316-319). Like the specimens from Cameron County examined by Sutton (op. cit.), our birds are intermediate in size between average-sized individuals of the two named subspecies. In color and pattern, we find that our specimens in breeding plumage fall within the range of variation of C. s. semipalmatus as exemplified by five specimens in nearly identical states of wear and fading in the Museum of Natural History.

On the basis of the evidence presently available, we are reluctant to follow Sutton (1950:136) in assigning breeding birds from the Gulf coastal region to C. s. inornatus, a name otherwise applied to a population of birds breeding inland, in northwestern North America south to central Utah and Colorado and east to South Dakota (and formerly to western and southeastern Minnesota and Iowa; see A.O.U. Check-list, 1957:190). The intermediate characters of birds breeding in coastal Texas and Tamaulipas probably represent not the results of actual genetic intermixing of the two named populations but, rather, an adaptive response of the eastern coastal stock (C. s. semipalmatus) to environmental modalities distinct from those operating elsewhere within the range of the eastern coastal population or on the inland population. Accordingly, we tentatively use the name C. s. semipalmatus for our Tamaulipan specimens, realizing that the patterns of geographic variation in the species do not lend themselves well to taxonomic treatment by the trinomial nomenclatural system. The need for a comprehensive analysis of geographic variation in this species, based, if possible, on proper segregation of age classes along the lines followed by Pitelka (1950) for Limnodromus, is obviously indicated.

PLATE 5

Map of coastal Tamaulipas, showing the barrier island and localities mentioned in text. Stippled areas are extensively marshy.

(Click on image for larger view.)

PLATE 6

Fig. 1.—Croton and Fimbristylis on stabilized dunes; the Laguna Madre and surrounding alkaline flats and clay dunes are visible in the background. Habitat of Road-runner, Ord kangaroo rat, and keeled lizard.