Mute Swan, Cornell Lab of Ornithology. Retrieved on 2011-12-18.
doi.org
Squires, J.R. and Anderson, S.H. (1997). "Changes in trumpeter swan (Cygnus buccinator) activities from winter to spring in the greater Yellowstone area". American Midland Naturalist. 138 (1): 208–214. doi:10.2307/2426667. JSTOR2426667.{{cite journal}}: CS1 maint: multiple names: authors list (ลิงก์)
Squires, J.R. and Anderson, S.H. (1997). "Changes in trumpeter swan (Cygnus buccinator) activities from winter to spring in the greater Yellowstone area". American Midland Naturalist. 138 (1): 208–214. doi:10.2307/2426667. JSTOR2426667.{{cite journal}}: CS1 maint: multiple names: authors list (ลิงก์)