AMERICAN DIPPERS NESTING NEAR JUNEAU, ALASKA 
but the observed fidelity of breeding dippers to a site and watershed implies 
that emigration was low. 
We fit a series of Cormack-Jolley-Seber mark-resight models (Williams 
et al. 2001) to the observations of dippers. These models estimated annual 
survival (()>) and detection probabilities (p); ((> is the probability that a bird 
alive and in the study area in one year is still alive and in the study area 
the following year, and p is the probability that a bird alive and in the study 
area during a year is detected during the surveys in that year. All marked 
birds were adults of unknown age (n = 113), so estimates apply to adults 
but are not age-specific. Because we suspected that survival might be a 
function of winter weather, we used the number of days with temperatures 
<-12°C as an index of weather conditions, a criterion chosen arbitrarily 
(-12°C « 10°F; local weather stations record temperature in Fahrenheit). 
Such cold days were numerous in months with average temperatures <1°C, 
a criterion applicable to the White-throated Dipper (C. cinclus) of Eurasia 
(Loison et al. 2002, Ssether et al. 2000; see Willson and Hocker 2008a). 
Temperatures were available from multiple local sources, all near sea level 
(see Willson and Hocker 2008a); when sources differed in the number of 
cold days, we used the minimum plus 0.5 (i.e. , >10 days became 10.5). 
Because only one marked bird (female) had a gap in its sighting history (i.e., 
resighted after having been unobserved for >1 year), we assumed that the 
probability of birds being resighted did not vary by year or sex [i.e., p(.)]. 
Initially, we fit a model that allowed survival probability to vary by year and 
sex, including sex-specific effects of the number of cold days (i.e., separate 
survival estimates for each year for each sex with weather affecting the sexes 
differently). After fitting the initial model, we fit simpler models that pooled 
survival estimates by sex or year or excluded the effect of number of cold 
days. We evaluated the fit of our most general model [(j)(year x sex + cold 
days x sex), p(.)] (i.e., we estimated an overdispersion factor c; Burnham 
and Anderson 2002) by using the median c goodness-of-fit procedure in the 
program MARK (version 5.1). We compared models by using the change 
(A) in the small-sample version of Akaike’s information criterion adjusted for 
lack of fit (i.e., QAICc) (Burnham and Anderson 2002), which we used to 
estimate each model’s weight, a measure of support for each model relative 
to the other models considered. 
RESULTS 
Streamflow and Occurrence of Nesting Dippers 
Dippers occupied territories on many of the streams in our study area 
(Figure 1). However, nesting dippers were not observed on streams with 
an estimated summer low-flow exceedance of less than about 0.4 cubic 
feet per second (n = 10; Figure 2), even though several of these streams 
had cliffs and boulders seemingly suitable for dipper nests (as judged from 
known nest sites). One of these small streams had been used for nesting at 
least once in the past. 
Seven of 10 streams with exceedances between 0.4 and 0.99 cubic feet 
per second were usually occupied during this study, two were not occupied, 
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