Effects of pcb's, pcdd's and pcdf's on reproductive success, and morphological, physiological and biochemical parameters in chicks of the Common term (Sterna hirundo) : a joint research performed in 1991/1992 : part I: Field study

Eight colonies. spread over the country and in areas differing in degree of contamination were selected. This enabled a comparison of colonies in a range from 'relatively clean' to 'heavily contaminated'. In these colonies two groups of possible effects were considered: ecological and toxicological. In this report the ecological studies will be presented. The ecological studies included all parameters of breeding biology potentially affected by contaminants. These are: laying date, clutch size, egg volume, laying interval, incubation time, hatching success, growth of young, developmental abnormalities in young, fledging success. Together with factors like food availability, weather, predation etc. these parameters determine the final breeding success. Breeding success in the colonies has to be compared with data from other colonies, especially with those from (relatively) unpolluted areas. A detailed analysis of breeding biology data is required in order to assess the factors causing differences between colonies. Of course other factors than pollutants have to be taken into account at this point as well. Especially the phase in which losses occur and the cause of these losses provide important information on which factors mainly determine breeding success.