Breeding Biology of the American Goldfinch in Ohio

The American Goldfinch (Spinus tristis) has been rather thoroughly investigated in the Midwest.However, much can be learned by using comparative methods that examine temporal and spatial patterns of variation within the species and between goldfinches and other species.The present investigation is a contribution toward this objective. PRO CEDURESThe study area of 50 acres was inside the city limits of Toledo, Ohio and consisted mainly of wet prairie and deciduous scrub forest habitat.Man-made ditches carry off excess water and although several fields were used to raise wheat and soybeans, the majority had not been tilled for 10 to 20 years.This decline in agriculture gave the goldfinches a good habitat, since fields that had been tilled perhaps two or three years previously had a growth of numerous forbs and thistles.Brushy hedgerows separated the old fields, and these, together with the second-growth vegetation in the fields and ditch banks, supplied numerous nesting sites.The area was studied for three years in the summers of 1963, 1964, and 1965.Daily visits were made in the field from the spring to fall of each year except in 1963, when observations began in late June, and in 1965 when they were ternfinated in late August.Nest dimensions were measured to the nearest one-half centimeter directly after completion and excluded strings of material other than the primary structure.The lesser and greater depth of the nest bowl were obtained.Some nests were measured again after nestlings had fledged to determine the expansion of the nest bowl and its possible effect on nestling survival.Eggs were marked with finger-nail polish in the sequence of laying in 1964 and 1965, and the dimensions of the lesser and greater diameter were measured with calipers to the nearest one-half millimeter.Eggs from all three years were weighed to the nearest one-tenth gram on the day following the laying of the last egg.The egg shape index (Beer, 1965) was calculated for the eggs in sequence of laying and for the total number of eggs.The index is in terms of percent and indicates ratio of length to width.lesser diameter x 100 greater diameterThe time of day when eggs were laid was determined by visiting some nests two or three times.Brown-headed Cowbird (Molothrus ater) parasitism was also recorded.The weights and sizes of eggs and of the egg clutches were compared for different months to find if there was a decline in clutch 26