Organochlorines and reproductive success of birds in orchard and non-orchard areas of central British Columbia, Canada, 1990-91

Most orchards in British Columbia, Canada and the northwestern United States received substantial applications of DDT in the mid-1940s through the early 1970s. Bird eggs were collected from orchard and non-orchard areas in the Okanagan Valley fruit-growing region of central British Columbia during 1990 and 1991 to determine levels of DDT, DDE, and other organochlorines. American robin (Turdus migratorius) eggs from orchard areas contained extremely high levels of both DDE (up to 103 mg/kg) and DDT (up to 26 mg/kg). For robins, tree swallows (Tachycineta bicolor), and house wrens (Troglodytes aedon), levels of DDT and DDE in eggs were significantly higher in orchard habitats than in non-orchard habitats. These data suggest that Okanagan Valley birds were acquiring DDT and DDE burdens locally, and not on their Latin American wintering grounds, as has been previously hypothesized. Ratios of DDE to DDT in robin eggs were quite low (<10), implying that DDT is not breaking down readily in orchard soils and/or that orchards have been receiving recent illicit applications of DDT. There was no evidence of lower reproductive success among tree swallows, house wrens, and bluebirds that nested in orchard versus non-orchard habitats, so the levels of DDT and DDE contained in their eggs (≤0.1 and ≤5 mg/kg, respectively) were probably not deleterious. There was no difference in reproductive success of robins nesting in conventional versus organic orchards. Although we did not have a sufficient sample of non-orchard robin nests, comparisons with data on reproductive success in the literature indicates that despite exceedingly high DDT and DDE concentrations, reproduction was not affected. Levels of other organochlorines (dieldrin, heptachlor epoxide, PCBs) in eggs were low, and usually below the minimum detectable threshold. The high DDE concentrations in these eggs from the Okanagan valley indicate that DDE body burdens of passerines nesting there would probably present a considerable toxic hazard to predators, particularly birds of prey.