Nutrition of Tree Sparrows during Winter in Central Illinois
1967
West, George C.
Stomach analyses of 131 tree sparrows (Spizella arborea) were made from birds collected from November through March, 1954—1959, near Urbana in Champaign County, Illinois. Simultaneously, 119 collections of seeds from the ground and 452 collections of seeds falling into seed traps were taken and the dry weight in grams per hectare per winter and the relative proportion of different species of seeds available by weight calculated. Seedfall occurred throughout the winter, but in the majority of species 75% or more of the seedfall occurred from September through November. Once on the ground, only 40% of the seeds of most species remained in a condition usable by birds the following year. Grass seeds, primarily Setaria spp., made up 77.7% of the winter diet. However, grass seeds made up only 38.8% of the seeds available on the ground and 44.6% of the seeds falling to the ground during the winter. Tree sparrows selected seeds of low gross energy content in comparison with those seed species not selected. The heat of combustion per gram dry weight of the average stomach contents did not change significantly during the winter and averaged 4690 cal/g. The average projected existence energy requirements of wild tree sparrows during winter was found to be 27.38 kcal/bird/day or equivalent to approximately 7.88 g of seeds (of the average winter diet) per day. On this basis it is possible for individual species of seeds to support flocks of 10 to 20 tree sparrows per hectare for the winter season in central Illinois.
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