Interesting Dipper behavior

[Jeff Kehoe]

I live in the Big Thompson canyon and see Dippers every day.  On the ice right behind my house a patch of nasty looking foam has been building up just below some open water (see photo).  Every day I see Dippers walking on the ice and picking at the foam.  I figured maybe there are some bugs stuck in it or something.  Anybody have any idea what they might be eating?

[Jeff Kehoe]

I was able to collect some of the foam from the river.  With David Leatherman's help we found that midges (Chironomidae) were stuck in the foam.  This is probably what the dippers were feeding on. Looks like some algae too.  Thanks David!