Relationships between behavior and the inhibition of acetylcholinesterase in birds exposed to organophosphorus pesticides

Effects of sublethal acute doses of the organophosphate chlorfenvinphos on the behavior of captive starlings ( Sturnus vulgaris ) were investigated in four experiments. Effects were more complex and occurred at lower levels of exposure than in previous avian studies. Altered posture was associated with inhibition of brain acetylcholinesterase (AChE) activity to less than about 88% of the normal level. Reductions in flying and singing, and increased resting, were associated with inhibition of AChE to below 61 % normal. Substantial recovery of normal behavior occurred within 5 h of treatment. Feeding activity was reduced for over 8 h in birds with AChE inhibited to less than about 73% normal, accompanied by a proportionate loss of body weight. Flying activity was initially depressed for 1 to 2 h but then increased above normal levels. Singing of isolated males in response to the playback of recorded song decreased in proportion to the inhibition of AChE. Performance of a foraging task was unaffected by inhibition of AChE to as little as 57% normal. A review of relevant studies suggests that only broad generalizations, of limited practical value, can be made about the relationship between AChE inhibition and behavioral effects.