Eggshells of Arctic Terns from Finland: Effects of Incubation and Geography

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Abstract
Eggs (74) from 7 colonies of Arctic Terns (S. paradisaea) in the Quark and the Bothnian Bay of Finland were collected in 1981 shortly after laying and immediately before hatching. Shell thickness, weight, thickness index and egg wt index were determined and compared with the same characteristics of 200 eggs collected between 1874 and 1935. No significant differences were found in these measures of egg thickness between recent and museum shells from the same geographical areas. Shells of museum specimens from different geographical regions did show significant variations. The weight and the wing and tarsus length of the embryos correlated negatively and significantly with all measured characteristics of the shell except its thickness when the shell membranes were present. During the incubation period, the shell''s thickness (without membranes) decreased 8%; thickness index and weight decreased 4%; and the shell''s thickness with shell membranes present decreased 1-2%. These changes are discussed in the light of pesticide related reproductive failure.