Tweets,
Contacted Roarke Donnelly who did his Master's on Dipper behavior in Utah on
the lakes discussion we've been having. He agreed on Rob's hypothesis about
flying up to lakes during breeding season and taking it back downstream.
Below are Roarke's comments:

"Regarding the dips...When I studied dippers in NE Utah, they did roam to
headwater lakes after breeding season. I never found a nest on a lake,
but I primarily looked for nest along rivers. I concur that most birds
observed on lakes during the breeding season are either floaters or
nesting on the stream and ferrying food from the lake to the nest below.
The Utah population had pretty strict nest site requirements (e.g.,
inaccessible midstream boulder or sheer streamside rock face). In
Montana, they appear to be more flexible regarding nest site selection
and will occasionally nest among roots in stream banks. I suppose that
means the Montana birds might also nest along a bank on a lake."

Scott Downes
downess at charter.net
Yakima WA