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Show -. Notes on Food Habits of the Thick-billed Red-winged Blackbirds in Utah' By JEAN H. LINFORD2 Specimens of the subspecies Agelaius phoeniceus fortis Ridgway, collected from Northern Utah, have bills that are moderately long and stout, but very sharp-pointed and without any noticeable curve of the culmen. The ratio of bill depth to length was 0.53 and 0.57 respectively for four adult males and A considerable degree of specialization for seed-eating two adult females. is thus shown, although the original adaptation evidently was for insect food. The manner of feeding is rather slow, and "deliberate" as compared with that of the Brewer Blackbird, Euphagus cyanocephalus (Wagler). Except during the breeding season the red-wings tend to feed in flocks; in September and October these have been estimated to consist of as many as two to three hun dred birds of both sexes and of all ages. During the winter months smaller flocks (usually less than one hundred) have been observed foraging in patches of sedge and cocklebur that were present along the edges of open bodies of In such patches many seeds of these plants are exposed through the water. rapid melting away of snow immediately after it has fallen. These seeds and those of sunflower were the chief sources of winter food. In order to de termine which kinds of food were taken at various months of the year, numerous observations on feeding birds were made and in most cases notes were recorded in regard to plant and animal materials available in the locality on the date that specimens were collected. Stomach contents of forty-five birds were analyzed, these being taken chiefly from Northern Utah areas during various months of the year. Although the number of stomachs ex amined was insufficient for drawing very general conclusions, the kinds of organisms taken as food on the various dates of collection were determined. Also certain general tendencies were noted from field observations. The re sults of the stomach analyses are given below. Three specimens were taken October 14, 1933, from a point along the Jordan River three miles northwest of Salt Lake City. One stomach con tained 42 sunflower seeds (H elianthus annus L.), 665 salt grass seeds (Echi nochloa crusgalli subsp.), 3 unidentified seeds, and 3 adult Diptera, (Antho myiidae 2, and Ortalidae 1). The other two stomachs both contained numer out pieces of sunflower seeds. One stomach had in addition 2 salt grass seeds, while the other had 1 sedge seed (C arex sp.). Two additional specimens were taken from the same locality on October 21, 1933. The stomachs contained the following seeds: 14 of salt grass, 1 of sedge, numerous sunflower seed hulls, and 6 other unidentified seeds. The stomachs of two birds collected November 19, 1933, from the Bear River Bay Bird Refuge contained 6 seeds of sunflower, 126 of sedge, pieces of approximately 3 cocklebur seeds (Xanth ium sp.), and 17 additional unidentified seeds. Two stomachs obtained from specimens taken January 14, 1934, at a point six miles south of Salt Lake Data taken largely from the writer's unpublished master's thesis: "The Life His tory of the Thick-billed Red-winged Blackbird, Agelaius phoeniceus fortis, Ridgway, in Utah," University of Utah, 1935. Acknowledgments are due to pr. A. M. Wood bury, Dr. R. V. Chamberlin, and Dr. W. P. Cottam for guidance and assistance during work on this thesis. Teaching Assistant in Zoology (1937-38), Utah State Agricultural College, Logan. . 2 91 |
