Organochlorine Residues in Aquatic Birds in the Canadian Prairie Provinces

A survey was conducted of organochlorine residues in 21 aquatic bird species at 31 locations in Alberta, Saskatchewan and Manitoba. As DDT and DDD residue levels from analyses without PCB separation proved to be unreliable, they were omitted from the results. DDE and dieldrin levels were higher in eggs of larids and fish-eating birds than in those of geese and ducks, presumably reflecting different trophic levels between those two groups of birds. Interspecific differences of DDE, dieldrin, HE and f BHC residues observed in larids and fisheating birds at the same breeding localities may reflect interspecific differences of feeding habits. DDE, dieldrin and PCB levels may be predicted in tissues of California Gull females when known in their eggs. Residue levels in eggs closely resembled those in the livers of females at the time of laying. Shell thickness was significantly and inversely correlated with the concentration of DDE in 40 Great Blue Heron eggs from Alberta, but no significant correlation was found between the concentration of PCBs and shell thickness in those eggs.