His flight is solid and impetuous, without any intermission of
wing-beats,--one homogeneous buzz like that of a laden bee on its way
home. And while thus buzzing freely from fall to fall, he is frequently
heard giving utterance to a long outdrawn train of unmodulated notes, in
no way connected with his song, but corresponding closely with his
flight in sustained vigor.
Were the flights of all the ouzels in the Sierra traced on a chart, they
would indicate the direction of the flow of the entire system of ancient
glaciers, from about the period of the breaking up of the ice-sheet
until near the close of the glacial winter; because the streams which
the ouzels so rigidly follow are, with the unimportant exceptions of a
few side tributaries, all flowing in channels eroded for them out of the
solid flank of the range by the vanished glaciers,--the streams tracing
the ancient glaciers, the ouzels tracing the streams. Nor do we find so
complete compliance to glacial conditions in the life of any other
mountain bird, or animal of any kind. Bears frequently accept the
pathways laid down by glaciers as the easiest to travel; but they often
leave them and cross over from canon to canon.
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