AMERICAN DIPPERS NESTING NEAR JUNEAU, ALASKA 
substrates harbor more benthic macroinvertebrates than fine substrates (see 
Willson and Hocker 2008a). Categories of gradient followed those of the 
Environment and Natural Resources Institute (ENRI), University of Alaska- 
Anchorage (Major and Barbour 2001), which uses the English system, here 
converted to the metric system: high, >122 cm in 15 m (>4-foot rise in 50 
feet); medium, 30-122 cm in 15 m (1- 4-foot rise in 50 feet); low, <30 cm 
in 15 m (<1 foot rise in 50 feet). We assessed gradients by measuring 15 
m (50 feet) along the stream and sighting horizontally from the upper end 
of the section to the lower; the distance between the water surface and the 
intersection of the horizontal line of sight with a vertical object at the lower 
end of the 15-m section gave the amount of rise. 
We also recorded type of forest canopy (coniferous or deciduous) and 
degree of canopy closure over the stream (ranking the width of the canopy 
opening above each of the five points sampled in a territory core) because 
previous studies documented effects of these variables on stream inverte- 
brates (e.g., Hawkins et al. 1982, Allen et al. 2003, Kelly et al. 2003). We 
do not discuss this information further, however, because it proved relatively 
uninformative: territory cores were distributed quite evenly over the full range 
of both canopy type and closure categories; the sole exception was a lack of 
territories on small streams where canopies were fully closed. 
During the nesting season in 2004 and 2005 we sampled benthic macro- 
invertebrates in the riffles of a number of stream reaches, both occupied (n 
= 21, at various elevations in 14 watersheds) and unoccupied (n = 10, all at 
low elevation) by dippers. In occupied streams we took samples in reaches 
known to be used by foraging dippers and accessible to us; in small, unoc- 
cupied streams we took samples in downstream reaches, where stream flow 
was as high as possible, to minimize the effect of stream size. Sampling took 
place in May (early in the nesting cycle) in 2004 and in June and July (when 
many pairs were feeding chicks) in 2004 and 2005. Sampling methods were 
based on those of ENRI (Major and Barbour 2001). Each sample consisted 
of five subsamples in units about 46 cm square, spread over at least 25 m 
of stream, and pooled. We disturbed the substrate manually to a depth of 
about 5 cm and brushed rocks to dislodge invertebrates, which were swept 
by the current into the kick-net downstream. Macroinvertebrates (>4 mm in 
length) were counted and identified at least to family. Densities are presented 
as numbers per sample. Dippers also pick drifting invertebrates from the 
water column and water surface (pers. obs.), but these potential prey items 
were not sampled. At the same time we sampled macroinvertebrates, we 
also measured the pH and temperature of the water. 
Survival Analysis 
We banded adult dippers with one USFWS aluminum band and three col- 
ored plastic bands for identification of individuals. Birds were caught in mist 
nets placed across the stream while the adults were feeding chicks. Captured 
birds were banded, weighed, and sexed by presence or absence of a brood 
patch (developed by females only). All birds were released on site after be- 
ing banded. Estimated apparent annual survival was based on resighting of 
banded adults the following year. This is, necessarily, “apparent” survival 
because we do not know the frequency of emigration from the study area, 
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