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Breeding Behavior and Nesting of the Eastern Robin

Howard Young
The American Midland Naturalist
Vol. 53, No. 2 (Apr., 1955), pp. 329-352
DOI: 10.2307/2422072
Stable URL: http://www.jstor.org/stable/2422072
Page Count: 24
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Breeding Behavior and Nesting of the Eastern Robin
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Abstract

The breeding behavior and nesting activities of the robin were studied at Madison, Wisconsin, during the years 1947 to 1949, inclusive. Pair formation in the robin apparently does not involve complex vocal, postural or behavioral modifications. Robins are usually monogamous and pair for the breeding season. Rematings in successive years are probably due to chance. Several examples of non-functional sexual activity were noted. Nesting started in early April and extended to late July. Nest construction (32 nests) took from 3 (1 case) to 18 days (1 case) with an average of about 7 days. Nest height (202 examples) varied from 2 to 30 feet with an average of 7.4 feet. Individual birds did not show any preference for a given height range. Nests irt solid plantings were usually peripherally located. The earliest date for a first egg was April 12; the latest date for a first egg was July 22. Oviposition usually started 3 or 4 days after the nest was completed. Eggs were ordinarily laid at the rate of 1 a day; the average clutch was 3.4 ± .05 eggs. Incubation was done by the females; average duration was 12.5 ± days. The earliest fledging was on May 11, the latest on August 18. The average time spent in the nest after hatching was 13.4 ± .13 days, the young leaving before they could maintain level flight. The young are dependent for about 2 weeks after they leave the nest. Fledglings wander widely; some become separated from their parents and are adopted by other adults. Success of robin nests varied from 32 (1949) to 62% (1948) with a 3 year average of 49%. Hatching success varied from 46 (1949) to 66% (1948) with a 3-year average of 58%. The percent of young fledged varied from 61 (1947) to 93 (1948) with a three-year average of 78. Considering each egg as a reproductive attempt, the robins nesting in the Forest Hills Cemetery (1948) were the most successful group, raising young from 58% of their eggs. No relationship was found between nest success and nest density, nor between nest success and nest elevation. A life curve for the robin, including egg mortality, is presented. The longest period of residence on the breeding grounds was 141 days. Analysis of hypothetical population, based as much as possible on field data, suggests that a nesting success, of about 60%, with an average annual production of 5 to 6 young per pair, associated with an approximately 75% mortality among young before autumn, and a 52% per annum mortality among adults, would result in a stable population.

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