Abstract
Free-living female red-winged blackbirds (Agelaius phoeniceus) were captured on their nests and given oral doses of 0, 2.37 or 4.21 mg/kg methyl parathion in a propylene glycol carrier during incubation. Birds were released immediately after dosing and observed for 5 h to document behavioral effects, amount of time spent off the nest after dosing and time spent incubating. Each nest was monitored until nestlings fledged or until all nestlings died or disappeared. For each nest, the time of abandonment, hatching success and fledging success were determined. In addition, prefledging weights were obtained for all nestlings in nests at 8 d after hatch. Although methyl parathion caused ataxia, lacrimation and lethargy and significantly depressed cholinesterase activity (>35%) at 4.21 mg/kg, there were no apparent adverse effects on reproduction. Females receiving 4.21 mg/kg methyl parathion were able to return to their nests, resume incubation, successfully hatch their clutch and rear their young. Nestlings of poisoned females did not have significantly different body weights at 8 d compared to controls, indicating that methyl parathion did not disrupt the females' ability to forage and deliver adequate food to nestlings. Band returns from the following year indicated that treatment birds returned and nested in nearly the same proportion as did controls and other red-winged blackbirds occupying the ponds. There was no indication that a single oral dose of methyl parathion (2.37 or 4.21 mg/kg) decreased over-winter survival.
Published Version
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