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A long-term study was initiated in 1992 to investigate whether elevated Hg exposure measured in Wisconsin common loons was associated with reduced reproductive performance or survival. Adults loons (n = 99)and chicks (n = 56) were captured on 45 lakes during 1992 and 1993, each was individually color-marked with plastic leg bands, and blood and feathers were collected for Hg analysis. Adult return rates and reproductive outcome were then recorded for the 45 lakes from 1993 to 1996. A significant linear relationship was observed between lake pH and log-transformed adult blood Hg (r2 = 0.22, p < 0.01) and chick blood Hg (r2 = 0.56, p < 0.001) concentrations. Egg Hg concentrations (mean = 0.9 q 0.3 mu g Hg/g fresh weight) were within the range associated with reduced hatching success or reduced survival of embryos or hatchlings in other sensitive avian species. Chick production was lower at lakes where chick blood Hg concentrationswere elevated. However, no relationship was observed between levels of adult Hg exposure and reproductive performance or annual adult return rates (an index of survival). Establishing a cause-and-effect relationship between Hg exposure and loon fitness is complicated by the negative correlation between lake pH and Hg exposure and potential confounding with other influences on productivity that may also be related to lake pH. [ABSTRACT FROM AUTHOR]

Total Hg concentrations were determined in blood and feather samplesof breeding common loons (Gavia immer) and their chicks from 24 lakes in Ontario with a range of water chemistry and fish Hg concentrations. In paired comparisons, males had significantly higher blood (p < 0.005) and feather (p < 0.05) Hg concentrations than their female mates. Sex differences in Hg concentrations were attributable to size differences between the two sexes and to the possible transfer of Hg toeggs by females during egg-laying. Significantly higher blood (p < 0.001) and feather (p < 0.01) Hg concentrations were found in adult loons compared to their chicks. Adult blood Hg concentrations were significantly correlated with those of their chicks (r = 0.62, p < 0.05).Adult blood concentrations averaged about 13 times those of corresponding chicks. Both adult and chick blood Hg concentrations were positively correlated with fish Hg concentrations (r = 0.71 and 0.51, respectively), indicating that adult loons in central Ontario, like theirchicks, probably feed mainly on their breeding lakes and reflect thefish Hg concentrations of those lakes. Three of 24 lakes had 20- to 50-g fish (mainly perch and sunfish) with Hg concentrations at or exceeding the critical concentration (0.3--0.4 mu g/g wet weight or ~ 1--2 mu g/g dry weight) reported to cause reproductive impairment in loons. Monitoring Hg in blood (adult and chick) and feathers (chicks only) is useful for assessing the local bioavailability of methylmercury and the degree of current dietary Hg exposure in loons and other piscivorous birds. [ABSTRACT FROM AUTHOR]

The common loon (Gavia immer) is a high-trophic-level, long-lived, obligate piscivore at risk from elevated levels of Hg through biomagnification and bioaccumulation. From 1991 to 1996 feather (n = 455) andblood (n = 381) samples from adult loons were collected between Juneand September in five regions of North America: Alaska, northwesternUnited States, Upper Great Lakes, New England, and the Canadian Maritimes. Concentrations of Mg in adults ranged from 2.8 to 36.7 mu g/g (fresh weight) in feathers and from 0.12 to 7.80 mu g/g (wet weight) in whole blood. Blood Hg concentrations in 3 to 6-week-old juveniles ranged from 0.03 to 0.78 mu g/g (wet weight) (n = 183). To better interpret exposure data, relationships between blood and feather Hg concentrations were examined among age and sex classes. Blood and featherHg concentrations from the same individuals were significantly correlated and varied geographically (r2 ranged from 0.03 to 0.48). Blood and feather Hg correlated strongest in areas with the highest blood Hg levels, indicating a possible carryover of breeding season Hg that is depurated during winter remigial molt. Mean blood and feather Hg concentrations in males were significantly higher than concentrations in females for each region. The mean blood Hg concentration in adults was 10 times higher than that in juveniles, and feather Hg concentrations significantly increased over 1 to 4-year periods in recaptured individuals. Geographic stratification indicates a significant increasing regional trend in adult and juvenile blood Hg concentrations from west to east. This gradient resembles U.S. EnvironmentalProtection Agency-modeled predictions of total anthropogenic Hg deposition across the United States. This gradient is clearest across regions. Within-region blood Hg concentrations in adults and juveniles across nine sites of one region, the Upper Great Lakes, were less influenced by variations in geographic Hg deposition than by hydrology and lak [ABSTRACT FROM AUTHOR]