Eggshell Removal by Laughing Gulls

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Abstract
Laughing gulls [Larus atricilla] remove eggshells from their nests at hatching. Flying from the nest was the most common method of disposal, although gulls also walked from the nest with shells, dropped them over the nest rim or used a combination of methods. The gulls'' tendency to remove shells was strong through incubation, but decreased sharply at hatching. On the basis of these findings and other comparative data, it is hypothesized that species disposing of eggshells and producing altricial young will show a strong tendency to do so during incubation, at and after hatching, whereas species whose young are semi-precocial and precocial will show a strong disposal response during incubation, but this responsiveness will be markedly reduced at and after hatching. Gulls habituated quickly to eggshells on the nest rim; if a gull did not remove a shell during the first 10 min of a test, it was unlikely to do so during an hour. The encapsulation of unhatched eggs by eggshells is an important selective factor that favors eggshell disposal.