Organochlorine pesticide contamination in neotropical migrant passerines.

Organochlorine pesticide levels were determined in Neotropical migrant passerines which have populations reported to be declining. Pesticide residues ranging from 0.385 to 27.4 ng/g were found in 19 of 21 birds, including both Hatch Year (HY) and After Hatch Year (AHY) age classes of nine different species. Eighteen of the 19 birds contained p,p'-DDE, while dieldrin was found in 16 birds and heptachlor epoxide was present in 10 birds. There were no significant differences in pesticide levels between HY and AHY birds, suggesting that HY birds are exposed to pesticides in their diet on the breeding ground or that pesticides are acquired from contaminated mothers, or both. Pesticide levels were not related to gender. Although the effects of these low residue levels on passerine fecundity are unknown, their presence has potential conservation implications for passerines and for the raptorial birds that feed upon them.