Thinner eggshells of dipper ( Cinclus cinclus ) eggs from an acidified area compared to a non-acidified area in Norway

Abstract

Eggs of dippersCinclus cinclus from a chronically acidified area in Southern Norway were compared with eggs from a non-acidified area in Central Norway. There were no differences in egg size, as measured by volume, weight, length and calculated surface area, between the two areas. Eggshells were 7.0% lighter and 6.1% thinner, as measured by the Ratcliffe index and 7.0% as measured by the eggshell index (shell weight/surface area) in Southern Norway than in Central Norway. The Ratcliffe and eggshell indices were highly correlated. Scanning electron micrographs showed that the palisade layer of eggshells of eggs from the acidified area was 10.7% thinner than that of eggshells of eggs from the non-acidified area. Eggshell vapour permeability was not significantly influenced by area. Since the moderately lower thickness in Southern Norway was not accompanied by higher vapour permeability, this indicates that the reduced eggshell thickness did not cause desiccation of dipper eggs in the acidified area. The possibility of underestimating the environmental effects of acidification on dippers is discussed.