Publication Date


Document Type


First Advisor

Southern, William E.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Biological Sciences


Ring-billed gull


A study was conducted in 1971 to determine if Ring-billed Gull (Larus delawarensis) adults are capable of recognizing their own chicks. Fifty nests, 50 adult pairs, and 128 chicks were marked and/or tagged for individual recognition. Observations of these birds indicated that some form of recognition system was present in this species. Only 4 (8%) natural permanent adoptions were recorded. In the remaining cases, (92%), the adults fed their own young exclusively from day of hatching until 30 days of age. Further investigations were made during 1972 to determine if adults were capable of discriminating between their own chicks and other juveniles present in the breeding area. Fifty nests were selected for observation, and the associated 50 adult pairs and 130 chicks were marked individually for identification. Chicks were substituted into nests from day of hatching through 10 days of age. A total of 100 trials were made representing 200 adult responses and 178 chick responses. By the time chicks were 9 days old, adults were capable of recognizing their own offspring, and strange chicks always were rejected and driven out of the nest territory. All substituted chicks, less than 9 days old, that approached vocalizing non-parents were accepted. Those that ran from the nest territory when adults vocalized were rejected. After the adults' own chicks were 9 days old, they rejected all strange chicks, regardless of the chicks' response to vocalizations. The selective advantages of a system of individual recognition are discussed for this colonial species.


Includes bibliographical references.


v, 39 pages




Northern Illinois University

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