Foraging Behavior and Survival in the Sierra Nevada Rosy Finch

Abstract

A tendency among naturalists today is to select for study animals which inhabit distant regions or those that are found only in inaccessible places. Remoteness adds appeal; the greatest treasures seem to exist in far off places. The author, realizing that some of the most common and accessible birds are often the least known, still yielded to this inclination, and selected as a subject for study the Rosy Finch (Leucosticte tephrocotis dawsoni) of the Sierra Nevada of California. Canyon, where these observations were made, is situated in the northern part of Yosemite National Park. It is just west of the crest of the Sierra, about thirteen miles north of Tuolumne Meadows, four miles west of Green Lakes Lodge, and fifteen miles south of Bridgeport. A stream, Return Creek, runs through it, first southward and then westward to join the Tuolumne River about fifteen miles east of Hetch Hetchy Reservoir. The greater part of this study was confined to the region of a great cirque which forms the extreme upper end of Canyon. In this report the term Virginia refers only to the Hudsonian and Arctic-Alpine zones of the canyon, of which the major part is included in the great cirque. The cirque is bordered on the east by Pass (10,600 feet) over which supplies were back-packed from our base at Green Lakes Lodge. The remoteness of the country and the difficulties of transportation were partly compensated for by the relief from human interference with the birds and their surroundings. The east side of the canyon is a single steep slope covered with Artemisia tridentata and other plants which are representative of the Great Basin flora. The west side is more typically Arctic-Alpine. The slopes here are broken by rock outcrops, small sedgecovered meadows, occasional moraines, and small lakes. Timberline follows the lower edge of the cliffs. The trees are stunted white-bark pines (Pinus albicaulis), and are concentrated on the small ridges and other high spots on the floor of the cirque. During the early part of the year these stand out like islands surrounded by a sea of snow. The cirque contains several small lakes and one larger unnamed one, about two acres in extent, which we called Leuco Lake. This lake is located on a shelf on the southwest side of the cirque. Observations in Canyon extended from June 14 to July 31, 1936, and from June 14 to July 25, 1937. A reconnaissance of about thirty miles of the crest of the Sierra Nevada north of Canyon was made from May 23 to 31, 1936. Four days of the same year, between August 15 and 19, were spent in Canyon. In 1937 a ski trip into Canyon was made from May 16 to 18 to observe the activity of the birds early in the season. During the first two weeks of January of both 1935 and 1937, I searched for birds on the mountains surrounding Echo Lake (7500 feet) in Eldorado County, but was unsuccessful. Two short trips in late fall were taken into the high country east of Yosemite to observe the habits of the birds at that season. My brother, Wilbur Twining, was my constant companion throughout the two periods of summer observations. Without his assistance this study would have been much more difficult, perhaps impossible. The rosy finch is an opportunist, living throughout the year on whatever happens to be the most abundant and readily obtainable kind of food. The food supply varies with the season and locality, and an analysis of rosy finch food habits must take these matters into consideration.