COMPARATIVE-STUDY OF THE SIGNS OF INTOXICATION AND CHANGES IN ACTIVITY LEVEL OF RED-WINGED BLACKBIRDS (AGELAIUS-PHOENICEUS) EXPOSED TO DIMETHOATE

Non-target wildlife are frequently exposed to organophosphate pesticid es such as dimethoate. While the causes of mortality have been reviewe d, much less is known of the potential danger of sublethal exposures t o these pesticides. In this work, the impact of lethal and sublethal d oses of dimethoate on red-winged blackbirds was investigated using two different approaches: visual symptoms of intoxication and fluctuation s in daily activity level. A series of symptoms was recorded in order of appearance with oral doses of dimethoate ranging from 0 to 1000 mg kg(-1) BW. Doses greater than or equal to 2 mg kg(-1) BW induced atara xia, followed by pilorection and dehydration (defecation and diarrhea) . Neuromuscular disfunctions and breathing complications appeared at 3 mg kg(-1) BW. Muscle paralysis and death were first observed with 5 m g kg(-1) BW, and all birds that ingested doses superior to 28 mg kg(-1 ) died. LD50 was estimated at 9.9 mg kg(-1) BW. Signs of intoxication lasted from 1.5 to 12.5 h. In contrast, the birds' activity level was affected during several days with doses lower than 6.7 mg kg(-1) BW. T wo opposite responses were observed: doses greater than or equal to 1. 34 mg kg(-1) BW initiated a 68-73% decrease in activity level, whereas doses less than or equal to 1.34 mg kg(-1) BW initiated a two-fold in crease in activity level These results suggest that the symptoms of in toxication may be useful to assess the degree of intoxication, and tha t the birds activity level is a more sensitive tool to estimate the ti me necessary for complete recovery. (C) 1997 Elsevier Science B.V.