One of the subscribers to The Psittacidae was Lord Stanley, heir to the Earl of Derby, and president of the Zoological and the Linnean Societies. At his father's estate, Knowsley, Lord Stanley had assembled a menagerie that was famous throughout Europe. Spread out over more than one hundred acres and tended by a staff of thirty, the Knowsley Menagerie included, at one time, 345 mammals of 94 species, and 1,272 birds of 318 species. Lord Stanley himself kept meticulous written records, and in 1832, he decided to find an artist to illustrate the collection. George Robert Gray, of the British Museum, suggested that he speak with Lear. Lord Stanley went to watch Lear sketch in the Parrot House, and hired him immediately. Lear lived and worked at Stanley’s estate for the next five years. These years shaped his life; at Knowsley the shy and awkward Lear was introduced to the upper echelons of society, and there he began to compose the Nonsense which would someday make him famous.

Lear produced hundreds of drawings and watercolor paintings while at Knowsley. Almost a decade later, in 1846, Lord Stanley had seventeen of Lear's paintings reproduced in Gleanings from the Menagerie and Aviary at Knowsley Hall.