I have no anecdotes about River Otters eating birds. But, Dalquest's
"Mammals of Washington" has a pretty good account of River Otters catching
on to the bat collecting activities of the author. In the San Juan Islands,
Dalquest would shoot a bat out of the air above the water and the River
Otters got so keen to what was going on that they would speed to the dead
bat and eat it before the author could retrieve it.

If they relish bats, they probably like birds, no?

Kelly McAllister