Abstract
The stomach contents of 402 adult male and 248 adult female red-winged blackbirds (Agelaitis phoeniceas) were analyzed for their total dry weight and caloric values to determine daily rhythms and seasonal changes between June 24 and September 10, 1966. The stomach contents were analyzed qualitatively by identifying and estimating the proportion of each food type. The mean caloric value of food in male redwings showed three peaks during the day and was significantly ( P < 0.01 ) higher before noon than after noon. Mean caloric intake of female redwings showed three peaks during the morning but no major peaks were demonstrated in the afternoon. Intake levels in tlle females were also higher in the morning. Mean caloric intake in June at the end of the breeding season was 211 cal/[bird gram X day] and in September, prior to autumn migration, was 246 [cal/bird gram X day]. Daily and seasonal peaks of the total energy intake represented changes in quantity of food consumed and changes in caloric content of ingested food. Daily and seasonal rhythms in activities of birds have been reported by many n7orkers. Among these studies are phenomena associated with bio-energetics. NIorning and late afternoon feeding peaks in birds, reported by Lees ( 1948 ), Beer (1961), Schmid (1965), and Morton (1967) represent the replenishing of depleted food reserves in the morning, and the rebuilding of food reserves towards evening in preparation for the night. Kendeigh ( 1949) and West (1960) have shown productive energy to be highest between April and October, when such energy-demanding activities as nesting, incubation, defense of territory, feeding of young, molting, and migration are undertaken. Thus it is logical to assume that daily and seasonal rhythms in bird activities are paralleled by daily and seasonal changes in energy consumption and must be related to internal energy requirements and external energy availability. The present study was designed to determine the daily and seasonal pattern of gross energy consumption in free-living, 1Present address: U. S. Bureau of Sport Fisheries and Wildlife, Blackbird Research Laboratory, Box 2097, Sandusky, Ohio 44870. adult red-winged blackbirds. The diet of redwings was also analyzed to compare southern Ontario results with the dietary shift in red-winged blackbirds as reported by Beal ( 1900 ) and Bird and Smith ( 1964 ), to ascertain the amount of corn in their diet, and to determine the frequency of insect occurrence. We wish to thank E. D. Bailey for providing the calorimetry equipment and for helpful criticisms; A. T. Cringan, A. L. Middleton, and K. Ronald for suggestions on the manuscript; D. H. Pengelly for aid in identification of the insect food; and F. H. Montgomery for assisting in the identification of plant food. This study was supported by the Ontario Graduate Fellowship Program and the Ontario Department of Agriculture and Food.
Published Version
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