. The Canadian field-naturalist. Natural history. 1970 Vermeer and Reynolds: Pesticide Residues in Birds 127 Table 10.—DDE and dieldrin residue ratios in tissues of 20 California Gulls from Edmonton and Joseph and Miquelon Lakes, Alberta in 1969. Tissue DDE Dieldrin comparisons Mean ratios ± SE Coefficient of correlation Mean ratios ± SE Coefficient of correlation Fat/liver Fat/brain Liver/brain ± ± ± ** ** ** ± ± ± * ** ** mon Terns. Although one highly contaminated gull, heron or tern may bias a mean composite s
. The Canadian field-naturalist. Natural history. 1970 Vermeer and Reynolds: Pesticide Residues in Birds 127 Table 10.—DDE and dieldrin residue ratios in tissues of 20 California Gulls from Edmonton and Joseph and Miquelon Lakes, Alberta in 1969. Tissue DDE Dieldrin comparisons Mean ratios ± SE Coefficient of correlation Mean ratios ± SE Coefficient of correlation Fat/liver Fat/brain Liver/brain ± ± ± ** ** ** ± ± ± * ** ** mon Terns. Although one highly contaminated gull, heron or tern may bias a mean composite sample, nevertheless a pooled sample is better than a single sample as an indicator of the degree of organochlorine contamination of a population. Two Great Blue Heron eggs with and DDE residue levels at Chip Lake, for example, had the highest DDE levels of all aquatic bird eggs collected. If one egg, low in DDE residues, had been sampled, there would be no indication that some herons at that locality were highly contaminated. The variation in individual DDE residue levels was smaller in Double-crested Cormor- ants than in Great Blue Herons, California Gulls and Common Terns (Table 7). Intraspecific variation in mean DDE residues between differ- ent localities was also smaller in cormorants, as well as in pelicans, than in California Gulls, Ring-billed Gulls, Common Terns, Herring. Y= - 0 4246 X r= ; 0 20 40 60 80 100 120 140 160 180 200 220 240 ppm ODE Figure 5. Relation between DDE concentrations and shell thickness in forty Great Blue Heron eggs from four Albertan heronries in 1969. Gulls and Great Blue Herons (Table 2). This may be related to the almost exclusively fish diet of cormorants as compared to the only partly fish diet of the gulls and herons. Cormor- ants probably are more restricted to feeding in deeper waters than terns, which have been observed feeding in very shallow bays as well as in ponds adjacent to the lakes where
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