In his earlier years Burroughs worked as a teacher and a farmer and for nine years as a clerk in the Treasury Department, Washington, D.C. In 1867 he paid tribute to his friend Walt Whitman in the book Notes on Walt Whitman as Poet and Person. In 1871 Wake-Robin, the first of his books on birds, flowers, and rural scenes, was published. Two years later he moved to a farm in the Hudson River valley and, from various retreats, wrote for half a century on nature subjects. His later writings showed a more philosophic mood and a greater disposition toward literary or meditative allusion than did his earlier work. His chief books, in addition to Wake-Robin, are Birds and Poets (1877), Locusts and Wild Honey (1879), Signs and Seasons (1886), and Ways of Nature (1905). He also wrote a volume of poems, Bird and Bough (1906). Burroughs traveled extensively, camping out with such friends as the naturalist John Muir and Theodore Roosevelt and accompanying an expedition to Alaska. Winter Sunshine (1875) and Fresh Fields (1884) are sketches of travel in England and France. His Whitman: A Study was published in 1896. Other collections of his essays are Time and Change (1912), The Summit of the Years (1913), The Breath of Life (1915), Under the Apple Trees (1916), and Field and Study (1919). The John Burroughs Association, a society to encourage writing in natural science, was established in his memory.