. The Canadian field-naturalist. 232 The Canadian Field-Naturalist Vol. 104 Residues (mg/kg). Residues (mg/kg) DIELDRIN HEPTACHLOR EPOXIDE 5 1 ^ 69 I I I I t t I I' 73 74 75 80 81 83 YEAR Figure 5. Changes in residue levels of organochlorine contaminants in eggs of Gryfalcons in northern Canada. nants could be discerned, although DDE, PCBs, heptachlor epoxide were highest in 1980 and 1981 (Figure 5). There were insufficient data from Atlantic Canada or British Columbia to permit analyses of temporal trends. Although raptors have been used to monitor changes i
. The Canadian field-naturalist. 232 The Canadian Field-Naturalist Vol. 104 Residues (mg/kg). Residues (mg/kg) DIELDRIN HEPTACHLOR EPOXIDE 5 1 ^ 69 I I I I t t I I' 73 74 75 80 81 83 YEAR Figure 5. Changes in residue levels of organochlorine contaminants in eggs of Gryfalcons in northern Canada. nants could be discerned, although DDE, PCBs, heptachlor epoxide were highest in 1980 and 1981 (Figure 5). There were insufficient data from Atlantic Canada or British Columbia to permit analyses of temporal trends. Although raptors have been used to monitor changes in environmental levels of persistent contaminants elsewhere ( Froslie et al. 1986), the extreme variability in both eggs and tissue levels due to individual and geographic differences in diet, migratory behaviour and exposure, makes it difficult to discern trends. From the sparse temporal data available, we can conclude only that dieldrin and DDE occurred at. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ottawa Field-Naturalists' Club. Ottawa, Ottawa Field-Naturalists' Club
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