Monitoring and Assessment of Swainson's Hawks in Argentina Following Restrictions on Monocrotophos Use, 1996-1997

During the austral summer of 1995-1996, about 6000 Swainson's hawks were found dead in the Argentina Pampas. Since most of these were attributed to the use of the organophosphate pesticide monocrotophos, the use of the compound was excluded for the 1996-1997 austral summer in the northern part of La Pampa. Of the 133 hawks monitored for organophosphate pesticide exposure only two showed signs of exposure to insecticides having anticholinesterase activity. The two having inhibited cholinesterase recovered. Washings of feathers and feet turned up one feather having dimethoate residue. None of the other washings showed the presence of organophosphate pesticides. Compared to reference values from North America, the hawks in Argentina had low acetylcholinesterase values in plasma. However, total and butyrylcholinesterase values were similar. No mortality of hawks was noted in the exclusion zone, although mortality of hawks continued outside of the zone.