The very idea of a bird is a symbol and a suggestion to the poet. A bird seems to be at the top of the scale, so vehement and intense his life.... The beautiful vagabonds, endowed with every grace, masters of all climes, and knowing no bounds - how many human aspirations are realised in their free, holiday-lives - and how many suggestions to the poet in their flight and song!
The Writings of John Burroughs: Birds and poets, with other papers (ed. 1904)