SUBSPECIFIC STATUS OF LEAST TERN POPULATIONS IN TEXAS: NORTH AMERICAN IMPLICATIONS
1992; Wilson Ornithological Society; Volume: 104; Issue: 2 Linguagem: Inglês
ISSN
1938-5447
AutoresBruce C. Thompson, Maureen E. Schmidt, S. W. Calhoun, Donald C. Morizot, R. Douglas Slacks,
Tópico(s)Fish Ecology and Management Studies
ResumoAnsrRncr.-Analyses of seven bill, leg, wing, and plumage characters measured from 267 museum specimens of adult Least Terns (Sterna antillurum) revealed significant morphological differences between sexes but not among three subspecies (antillarum, athalassos, and browni) currently recognized in North America. While individual morphometric characters sometimes did not overlap between a pair of subspecies, discriminant analysis employing criteria developed from the complete morphometric data set correctly classified >90% of antillarum specimens but misclassified 39% and 5 1% of athalassos and browni specimens, respectively. Cluster analysis did not segregate specimens into groups consistent with current subspecific taxonomy. Electrophoretic variation in proteins encoded by 50 loci revealed no genetic distinctions between S. a. antillarum and S. a. athalassos for 22 specimens from four breeding sites on the Texas coast, Rio Grande, and Texas panhandle rivers. These data illustrated continued difficulty in distinguishing endangered and nonendangered “forms” of the same species. Distinctions proposed in original descriptions of North American Least Tern subspecies are not sufficiently definitive; we recommend reassessment of subspecies within the entire species taxon. Received 20 May 1991, accepted 22 Oct. 1991. Three subspecies of Least Terns (Sterna antillarum, formerly S. albifions) are recognized from North America (A.O.U. 1957, 1983). Coastal Least Terns (S. a. antillarum) nest along the Atlantic seaboard from southern Maine (Hunter 1975) to Florida, the Gulf Coast, and Caribbean islands (A.O.U. 1957, 1983). Interior Least Terns (S. a. athalassos) breed in the Mississippi Valley; along tributaries of the Missouri, Arkansas, and Red rivers from North Dakota to Texas; and at scattered sites in the Rio Grande drainage of New Mexico and Texas (Hardy 1957, Downing 1980, Whitman 1988). California Least Terns (S. a. browni) are restricted to a breeding range along the Pacific Coast from San Francisco Bay, California, to Baja California, Mexico (California Least Tern Recovery Team 1980). Number and size of S. antillarum breeding populations have declined in recent times owing to disturbance or destruction of nesting and feeding habitat by shoreline development, dredging, diversion and impoundment
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