William Bartram (April 20, 1739 - July 22, 1823) was an American naturalist. The son of Ann (nee Mendenhall) and the naturalist John Bartram, William Bartram and his twin sister Elizabeth were born in Kingsessing, Philadelphia, Pennsylvania. As a boy, he accompanied his father on many of his travels to the Catskill Mountains, the New Jersey Pine Barrens, New England, and Florida. From his mid-teens, Bartram was noted for the quality of his botanic and ornithological drawings.

Bartram returned to Philadelphia in January 1777 and assisted his brother John in all aspects of running Bartram's Garden.  In the late 1780s, he completed the book for which he became most famous, Travels through North and South Carolina, Georgia, East and West Florida, the Cherokee Country, etc.. It was considered at the time one of the foremost books on American natural history. Many of Bartram's accounts of historical sites were the earliest records, including the Georgia mound site of Ocmulgee. In addition to its contributions to scientific knowledge, Travels is noted for its original descriptions of the American countryside. Bartram's writing influenced many of the Romantic writers of the day. William Wordsworth, Samuel Taylor Coleridge, and Francois-Rene de Chateaubriand are known to have read the book, and its influence can be seen in many of their works.  Although Bartram has often been characterized as a recluse, all evidence shows that he remained active in commercial, scientific, and intellectual pursuits well into the nineteenth century. He tutored nieces and nephews, penned a number of essays, contributed to several works anonymously, and helped run the family horticultural business. In 1802, Bartram met the school teacher Alexander Wilson and began to teach him the rudiments of ornithology and natural history illustration. Wilson's American Ornithology includes many references to Bartram and the area around Bartram's Garden. Among Bartram's more significant later contributions were the illustrations for his friend Benjamin Smith Barton's explanation of the Linnaean system, Elements of Botany (1803-04).  After the War of 1812, when many of his colleagues, contacts, and friends had died, Bartram settled into a long period of work, observation, and study at the family's garden in Kingsessing. He maintained a "Diary" that records bird migrations, plant life, and the weather. He refused a request to teach botany at the University of Pennsylvania, and in his sixties, declined an invitation from President Thomas Jefferson to accompany an expedition up the Red River in the Louisiana Territory, in 1806. He died at his home at the age of 84.

Answer the following question by taking a quote from the article: when did he return to philadelphia?
Bartram returned to Philadelphia in January 1777