Ecological investigations revealed differences in breeding success of cormorants (Phalacrocorax carbo) between two colonies in The Netherlands In this study the possible role of organohalogen pollutants was investigated. Thirty‐nine cormorant eggs were collected from two colonies with marked differences in contamination Seventeen cormorant eggs were hatched in an incubator. The respiration rate was monitored regularly during the incubation. Hatchlings were euthanized at day 1 Several morphological parameters were measured PCBs and polychlorinated dibenzo‐p‐dioxins (PCDDs) and dibenzofurans (PCDFs) were analyzed in the yolk sac Blood and liver were collected for analysis of cytochrome P450, ethoxyresorufin‐O‐deethylation (EROD) and pentoxyresorufin‐O‐depentylation (PROD) activities, vitamin A, and thyroid hormone levels. Residue levels differed two‐ to five‐fold for PCBs and 25% for PCDDs and PCDFs between both colonies Birds from the most contaminated colony showed an increased in ovo respiration rate, increased cytochrome P450 and EROD activity, and reduced plasma thyroid hormone and hepatic retinyl palmitate levels. Large interindividual differences were observed for all parameters The data were compared on an individual basis (n = 17) to detect any concentration‐effect relationships. Significant (p < 0 05) concentration‐effect relationships were observed for EROD induction, plasma free thyroxine reduction, yolk sac weight, relative liver weight, and head size. It is concluded these compounds may, at least in part, have played a role in the observed low breeding success of cormorants

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Ecological investigations revealed differences in breeding success of cormorants (Phalacrocorax carbo) between two colonies in The Netherlands In this study the possible role of organohalogen pollutants was investigated. Thirty‐nine cormorant eggs were collected from two colonies with marked differences in contamination Seventeen cormorant eggs were hatched in an incubator. The respiration rate was monitored regularly during the incubation. Hatchlings were euthanized at day 1 Several morphological parameters were measured PCBs and polychlorinated dibenzo‐p‐dioxins (PCDDs) and dibenzofurans (PCDFs) were analyzed in the yolk sac Blood and liver were collected for analysis of cytochrome P450, ethoxyresorufin‐O‐deethylation (EROD) and pentoxyresorufin‐O‐depentylation (PROD) activities, vitamin A, and thyroid hormone levels. Residue levels differed two‐ to five‐fold for PCBs and 25% for PCDDs and PCDFs between both colonies Birds from the most contaminated colony showed an increased in ovo respiration rate, increased cytochrome P450 and EROD activity, and reduced plasma thyroid hormone and hepatic retinyl palmitate levels. Large interindividual differences were observed for all parameters The data were compared on an individual basis (n = 17) to detect any concentration‐effect relationships. Significant (p < 0 05) concentration‐effect relationships were observed for EROD induction, plasma free thyroxine reduction, yolk sac weight, relative liver weight, and head size. It is concluded these compounds may, at least in part, have played a role in the observed low breeding success of cormorants