AMERICAN DIPPERS NESTING NEAR JUNEAU, ALASKA 
confidence interval 0.222-0.446) for years with 22.5 cold days (Figure 4). 
Model-averaged (Burnham and Anderson 2002) estimates were very similar 
to those produced by the best model (Figure 4). The estimated detection 
probability for both the best model and from model averaging was 0.939 
(95% confidence interval 0.758-0.987). 
During the years of this study, 61 (54%) of the 113 banded birds nested 
in only one year and 28 (25%) nested in two years. Only 24 (21%) nested 
in at least three years. 
DISCUSSION 
Dippers typically concentrate their activity on fast, clear mountain streams, 
often on reaches of relatively high gradient, constrained by steep walls (e.g., 
Kingery 1996, Loegering and Anthony 1999). However, we found some 
nesting territories centered on reaches of low gradient and fine substrates 
where anthropogenic structures provided nest sites. Dippers were able to 
nest along glacial streams, probably because they nested early, before the 
heaviest loads of sediment came down, and they commonly foraged in 
nearby tributaries and sloughs with clear water. 
All reaches of the streams we studied run through forested terrain, pre- 
cluding a comparison with the finding of Loegering and Anthony (1999) of 
the dipper’s apparent preference in Oregon for streams through forest over 
those through other habitats. From observations in Alaska and the Yukon 
Territory outside our study area (Darcie Neff, Auke Bay Laboratory, Juneau, 
pers. comm.; Willson pers. obs.), we do not think that American Dippers 
avoid unforested landscapes in our region. 
o 
7 12.75 18.5 24.25 30 
Days < -12o C 
Figure 4. The estimated relationship between probability of annual survival of 
dippers and the number of cold days (<-12° C) that year. Dashed lines indicate the 
95% confidence interval. Triangles are separate yearly survival estimates from model 
[<j>(year), p(.)l, and diamonds are the model-averaged yearly estimates (Burnham and 
Anderson 2002). 
201 
