Effects of exposure to an organophosphorus pesticide on the behavior and use of cover by captive starlings

Abstract

Abstract It has been suggested that reduced behavioral activity of birds exposed to anticholinesterase pesticides could bias measures of exposure in field studies if the worst-affected individuals were underrepresented in samples collected by shooting or netting. To assess the likely scale of such biases, European starlings (Sturnus vulgaris) were housed in large aviaries containing simulated bushes made from natural vegetation. Each bird was given a near-lethal dose of the organophosphorus pesticide chlorfenvinphos, and the proportion of time spent in and out of cover was recorded before and after treatment. Use of cover by exposed birds increased significantly 0 to 7 h after treatment, whereas feeding and flying activity decreased. On the following day, there was little difference in the use of cover by exposed and control birds. Mathematical models were used to estimate the effect of these behavioral changes on the sampling of birds from wild populations. The results confirm the potential for sampling bias to occur after acute pesticide exposure. This bias is reduced in samples taken over 24 h after exposure, but delayed samples are unlikely to be representative of cholinesterase (ChE) inhibition at the time of maximal effect. When poisoned birds seek cover, it is more difficult to find casualties in field trials and the probability that dead birds will be found and recorded in wildlife casualty monitoring schemes is reduced. We conclude that considerable caution is required in using ChE activity as an indicator of exposure in avian field trials.