AMERICAN DIPPERS NESTING NEAR JUNEAU, ALASKA 
1991). There is growing evidence for several species of passerines, includ- 
ing dippers, that calcium can be a limiting factor (see Ormerod et al. 1991, 
Obermeyer et al. 2006). 
The effects of pollution and sedimentation on the American Dippers have 
been studied less than for the Eurasian species. Price and Bock (1983) re- 
ported that a heavy input of sediment into a stream led to reduced density and 
reproductive success of the American Dipper. Feck and Hall (2004) found 
that dipper density decreased with decreasing abundance of favored prey 
insects but was only weakly related to several indices of stream quality. 
Cyanide in mine-tailing ponds has been lethal to many kinds of aquatic birds 
(Henny et al. 1994) and could pose a threat to dippers, including during the 
nonbreeding season, when dippers forage in many kinds of aquatic habitats 
(Willson and Hocker 2008a). Furthermore, mercury from mine tailings has 
detrimental effects on fish-eating birds (Henny et al. 2002), and in our area 
dippers commonly eat fish (Obermeyer et al. 2006, Willson and Hocker 
2008b). American Dippers are known to accumulate organochlorines, 
polychlorinated biphenyls, and heavy metals (including mercury) in eggs and 
chicks (Blus et al. 1995, Strom et al. 2002, Morrissey et al. 2004), though 
Henny et al. (2005) detected no effects of these contaminants on the dipper’s 
reproductive success. Exposure to lead decreases the activity of an enzyme 
essential for formation of hemoglobin and cytochromes (Blus et al. 1995, 
Strom et al. 2002) and can lead to decreased hematocrit and hemoglobin. 
Strom et al. (2002) found that decreased activity of this enzyme is associated 
with higher lead concentrations in the blood of adult and nestling dippers, but 
they did not assess the birds’ survival and reproductive success. For a small, 
active bird, any decrease in hemoglobin and cytochrome is likely to diminish 
its metabolic capacity and reduce its ability to deal with high demands for 
energy. The ability of the American Dipper to cope with heavy metals and 
other pollutants should be examined more thoroughly to assess at what level 
and under what conditions particular pollutants have negative effects 
ACKNOWLEDGMENTS 
The Alaska Department of Fish and Game nongame program funded much of our 
field work from 2004 to 2008. We thank Dave Albert, The Nature Conservancy, for 
the majority of the estimates of watershed area and Eran Hood, University of Alaska- 
Southeast, for instruction on estimating stream flow. Dan Bogan, ENRI at the Uni- 
versity of Alaska-Anchorage, instructed us on sampling of benthic insects in streams, 
and he generously lent equipment. Jamie Womble helped kick-start this program, 
and John Hudson helped with identification of benthic insects. Several field assistants 
hiked many miles, waded mountain streams or bushwhacked along them, and provided 
netting and banding expertise. Cheryl Cook captained the skiff used for the broader 
survey. Librarians at the University of Alaska-Southeast provided invaluable assistance. 
Thanks to Steve Matsuoka and an anonymous reviewer for constructive comments. 
We are also grateful to Maggie Hocker for moral support. 
LITERATURE CITED 
Allen, J. D., Wipfli, M. S., Caouette, J. R, Prussion, A., and Rodgers, J. 2003. Influ- 
ence of streamside vegetation on inputs of terrestrial invertebrates to salmonid 
food webs. Can. J. Fish. Aquat. Sci. 60:309-320. 
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