E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Eagle (in phrases).
Thy youth is renewed like the eagles (Ps. ciii. 5). This refers to the superstition feigned by poets that every ten years the eagle soars into the fiery region, and plunges thence into the sea, where, moulting its feathers, it acquires new life.