Effects of methyl parathion in ducks and duck broods

Nesting ducks (mallards, blue‐winged teal, cinnamon teal and wood ducks) were trapped, equipped with radio transmitters and released on two agricultural fields, both of which were bordered by waterways. One field was aerially treated with methyl parathion at the rate of 1.4 kg active ingredient (a.i.)/ha and the second field was an untreated control. Ducks were located with the aid of radiotelemetry after pesticide application and their activity monitored daily in both fields. Brood abandonment by hens and nesting hen mortality occurred only on the methyl‐parathion‐treated field postspray. Brain cholinesterase levels were significantly depressed in two of three nesting hens. Fifty‐eight percent of the 37 ducklings present in the control field on the day of spray survived to day 22 postspray. Sixteen percent of the 24 ducklings present in the treated field on the day of spray survived to day 22. The average daily rate of duckling loss was also greater in the treated field than in the control field. Nest abandonment rates could not be correlated with methyl parathion application.