Brain cholinesterase activity in fledgling starlings: Implications for monitoring exposure of songbirds to ChE inhibitors

Exposure of songbirds to organophosphate and carbamate pesticides is often determined by comparing the brain cholinesterase (ChE) activity of individuals that have been exposed with that of unexposed birds of the same species (e.g., see Busby et al. 1981, 1982; Hamilton et al. 1981). Knowledge of the normal pattern of ChE development in the brains of nestling and fledgling passerines is a necessary prerequisite for monitoring exposure to ChE inhibitors, and assessing the impacts of these inhibitors on the reproductive success and survival of songbirds. In a previous study, Grue et al. (1981) reported that ChE activity in the brains of wild nestling European starlings (Sturnus vulgaris), 3 to 18 days old, varied significantly with age and appeared to increase toward adult levels at a constant rate. Grue et al. (1981) hypothesized that if brain ChE activity continued to develop at a constant rate, levels in the brains of fledgling starlings about 28 days old would be comparable to those in the brains of adults. The present study was conducted to test this hypothesis.