THINNER EGGSHELLS OF DIPPER (CINCLUS-CINCLUS) EGGS FROM AN ACIDIFIED AREA COMPARED TO A NON-ACIDIFIED AREA IN NORWAY

Eggs of dippers Cinclus cinclus from a chronically acidified area in S outhern Norway were compared with egg's from a non-acidified area in C entral Norway. There were no differences in egg size, as measured by v olume, weight, length and calculated surface area, between the two are as. Eggshells were 7.0% lighter and 6.1% thinner, as measured by the R atcliffe index and 7.0% as measured by the eggshell index (shell weigh t/surface area) in Southern Norway than in Central Norway. The Ratclif fe and eggshell indices were highly correlated. Scanning electron micr ographs showed that the palisade layer of eggshells of eggs from the a cidified area was 10.7% thinner than that of eggshells of eggs from th e non-acidified area. Eggshell vapour permeability was not significant ly influenced by area. Since the moderately lower thickness in Souther n Norway was not accompanied by higher vapour permeability, this indic ates 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.