Rainfall preceding egg-laying - a factor of breeding success in Common Terns (Sterna hirundo).

The temporary reduction of clutch size, egg size and breeding success of the Common Tern during the breeding period of 1983 at the Lower Saxonian Wadden Sea (West Germany) was correlated with heavy rainfalls on the days preceding egg-laying (Figs. 2-4). Possible effective mechanisms and the result that the reduction of clutch size was not observed for colonies at the mainland coast are being discussed (Fig. 4).