Effects of methylmercury exposure on the behavior of captive-reared common loon (Gavia immer) chicks.
Behavioral effects resulting from exposure to dietary methylmercury (MeHg) have been reported in studies of several wildlife species. However, quantifying the impact of contaminant exposure on wild populations is complicated by the confounding effects of other environmental stressors. We controlled confounding stressors in a laboratory study to quantify the level of dietary MeHg exposure associated with negative effects on the fitness of captive-reared common loon (Gavia immer) chicks. We evaluated the effect of MeHg on loon chick behavior by employing several assays, including measures of righting reflexes, responsiveness to taped parental calls, reaction to frightening stimuli, and estimates of time activity budgets. Evidence suggested that as chicks aged, those exposed to nominal dietary dose levels of 0.4 and 1.2 microg Hg/g wet-weight in food (average estimated delivered dietary level of 0.55 and 1.94 microg Hg/g, respectively) were less likely (p < 0.01) to right themselves after being positioned on their backs during outdoor trials (> or =37 days old) compared to chicks on the control diet. We detected differences (p < 0.05) in several response variables with respect to source of eggs. Chicks from nests on low-pH lakes tended to spend more time on resting platforms, spent less time in the shade, were more likely to walk across a platform upon release and do it quicker, were less responsive to a frightening stimulus, and exhibited less intense response to parental wail calls than did chicks from neutral pH-lakes. Rapid MeHg excretion during feather growth likely provides loon chicks protection from MeHg toxicity and may explain the lack of behavioral differences with dietary intake. Lake source effects suggest that in ovo exposure to MeHg or other factors related to lake pH have consequences on chick behavior.