Paul Freedman, "American Restaurants and Cuisine in the Mid-Nineteenth Century", The New England Quarterly84:1:5-59 (March 2011), doi:10.1162/TNEQ_a_00066, pp. 36, 39
Larkin, Paul; Mercer. They can also be seen in Singapore. David (March 2004). "Canvasback in Kent: new to Britain". British Birds. 97: 139–144. ISSN0007-0335.