EFFECTS OF SUBLETHAL EXPOSURE TO AN ORGANOPHOSPHATE ON THE FLYING PERFORMANCE OF CAPTIVE STARLINGS

Organophosphorus compounds are widely used as pesticides and there hav e been many reported cases of the unintentional poisoning of wild bird s (Grue et al. 1983). These compounds inhibit cholinesterases includin g acetylcholinesterase (AChE), an enzyme which is essential for the no rmal functioning of both the central and peripheral nervous systems (G rue et al. 1983). Previous studies have shown that a fall in brain ACh E activity to 50% of normal can bring about changes in bird behavior ( Grue and Shipley 1981; Grue 1982; Grue et al. 1982; White et al. 1983; Gallindo et al. 1985; Kreitzer and Fleming 1988). The relationship be tween bird behavior and AChE over the range between 50% and 100% of no rmal AChE activity was investigated by Hart (1993). At low levels of e xposure there were subtle effects on behavior including changes in fly ing activity, singing behavior and posture. For example, at relatively low levels of exposure (AChE activity reduced to 88% of normal), bird s spent less time standing on one leg, perhaps because of impaired bal ance. Such effects of sublethal exposure may damage birds' survival or reproductive success. Slight effects on coordination during flight ma y increase the risk of collisions and possibly make a bird more vulner able to predation (Hunt et al. 1992). Less efficient flying may also r educe foraging success which could endanger the survival of adults and any nestlings they are feeding. This study tested whether flying perf ormance of captive starlings (Sturnus vulgaris) was affected by low le vels of the OP chlorfenvinphos (2-chloro-1-[2,4-dichlorophenyl]-vinyl diethyl phosphate). We measured birds' abilities to avoid collision wi th obstacles in the flight path between two food dispensers. Starlings were chosen as they have been the subject of previous studies on OP's and behavior (Grue and Shipley 1981; Grue 1982; Grue et al. 1982; Har t 1993). Chlorfenvinphos was used as we already have some understandin g of the relationship between exposure to this compound and the behavi or of starlings (Hart 1993).