Page:Condor16(5).djvu/21

Sept, 1914 211 A STUDY OF THE STATUS OF CERTAIN ISLAND FORMS OF THE (?ENus SALPINCTES By H. S. SWARTH (Contribution from the Museum of Vertebrate Zoology of the University of California) F SCARCELY less interest than those susceptible types of animals which, covering a vast expanse of territory, show wide variation in re- sponse to the difference in surroundings at different points, are the forms occasionally observed, just as wide ranging, and over a similarly varied region,. but still remaining uniform in appearance over most.or all of their habitat. Perhaps as striking an example of the latter class as exists in North America is the Rock Wren (Salpinctes obsoletus), the unyielding nature of whose characteristics is in strong contrast to the adaptability shown by other members of the same family of somewhat similar distribution, Thyromanes for instance. The present study, begun by the writer partly at the instance of Mr. Grin- nell, to ascertain, if possible, the true status of certain series from the Santa Barbara Islands, is based mainly upon the collection of Salpinctes contained in the Museum of Vertebrate Zoology of the University of California. In addi- tion to these specimens there were available the series from the Grinnell, Mor- eore, and Swarth collections, on deposit in the same institution; and also the collections of F. S. Daggett, and of George Willett, in the Los Angeles Museum of History, Science, and Art. The Grinnell, Daggett, and Willett collections contain large suites of skins from the Santa Barbara Islands. Of exceptional value and interest is a series of twenty-five skins kindly loaned me by Mr. John E. Thayer, containing birds from certain of the islands, including topo- types of S. obsoletus pulverius in newly acquired autumnal plumage. Much of the other island material available consists of spring and summer specimens, more or less worn and faded, and these fresh fall specimens give opportunity for comparisons not possible before. I wish here to express my appreciation and gratitude to those persons concerned for the privilege of' assembling and studying the material from the above mentioned collections. Perhaps the one feature brought most strongly to the writer's attention is, as mentioned above, the indifference shown by the species Salpinctes obso- letus to conditions forming absolute barriers to many other animals. It is true that our knowledge of the genus Salpinctes is rather unevenly distributed. By the latest authority on the group (Ridgway, 1904, pp. 643-653) it is regarded as composed of four species, one of these being divided into six subspecies, three mainland and three island forms. Of all these divisions of the genus, one subspecies, S. obsoletus obsoletus, is fairly well known, while it is probably safe to say that none of the others is thoroughly understood. It is evident, how- ever, that taking the distribution of the genus as a whole, extending from Cen- tral America over western North America to southern Canada, it is only at the southern limits of the range that there is any tendency toward a separation into well differentiated forms. Here, in a relatively restricted and unvaried portion of America, occur four recognizable forms, as contrasted with the one (S. obsoletus obsoletus) ranging over that part of the North American mainland which comprises about three-fourths of the habitat of the entire genus. Study of the range of the North American Rock Wren (S. o. obsoletus)