Studies on Deciduous Forest Animal Populations During a Two-Year Period with Differences in Rainfall

Publisher Website
Google Scholar
Abstract
A study of the invertebrate population of Trelease Woods, Urbana, Illinois, from Sept., 1933, through Oct., 1935, is presented. The invertebrate population was influenced by rainfall, temp., etc. The total herb-shrub population was larger in 1934, when rainfall was below normal in May and temps. for Mar. through Oct. were above normal, than in 1935, a yr. in which rainfall was above normal and temps. were lower than average. The ground-inhabiting species showed greater populations in the wet summer of 1935. Due to the large over-wintering population of 1934, the vernal (Mar. 1-May 31) population on the herbs and shrubs was greater in 1935 than in 1934. The aestival-autumnal (June 1-Oct. 31) population of resident spp. in 1935 was only 75% of the population for that period in 1934. Factors which influence migration of invertebrates into and out of hibernation are analyzed. The winter and migrant population of birds ranged from 400 to 600 on the 20-hectare area of woods and was 70% insectivorous. On one occasion robins took 5/6 of the hibernating insects in an area of 10 hectares. However, the largest number of migrating birds arrived when the migrating insect population was moving into or out of the woods; this population was probably 20 times that consumed by the birds. Examination of stomach-contents of birds indicated that the Lepidoptera, Hemiptera, larger Diptera, and Hymenoptera were the insects most often eaten; flea-beetles and other small forms were utilized to some extent.