AMERICAN DIPPERS NESTING NEAR JUNEAU, ALASKA 
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Occupied during study 
Known to have been occupied 
Not occupied 
G Glacial runoff streams 
L Lake-fed streams (natural) 
B Bog -fed streams 
(All other streams fed mainly by snowmelt) 
5 + - 1 0 
Individual Streams 
Figure 2. Streamflow (90% exceedance estimates in cubic feet per second, cfs) and 
occupancy by nesting dippers. Heights of vertical bars indicate streamflow, and 
streams are arranged on the x axis from smallest to largest. Streams originating in 
muskeg bogs (B), glaciers (G), or lakes (L) are indicated; all others originate in alpine 
zones. 
and one was occupied once in the recent past (Figure 2). Dippers nested on 
all monitored streams with exceedance > 1 cubic foot per second (n = 20) in 
at least two of the five years of our study. Nesting dippers were not found on 
any streams originating in muskeg bogs, including one of apparently suitable 
size. All three streams of glacial origin had nesting dippers, and all fledged 
young successfully in at least some years during this study. 
Stream reaches occupied by nesting dippers had higher densities of ben- 
thic macroinvertebrates (mostly Ephemeroptera, Trichoptera, and Plecop- 
tera in all samples) than unoccupied streams (Wilcoxon rank-sum test, normal 
approximation, June and July 2004 and 2005, score = 2.7, P = 0.0067; 
May 2004, score = 2.1, P = 0.016), but densities of macroinvertebrates in 
samples from many occupied reaches of streams were similar to those in 
unoccupied streams (Figure 3). 
Territory and Nest-Site Characteristics 
The width of the stream channel in the core of 52 dipper territories aver- 
aged from 2 m to >16 m. Most territory cores were located on medium- to 
high-gradient reaches whose substrates were chiefly bedrock and boulders 
or cobbles (Table 1). 
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