Because that kind of bird live in South Dakota and the researchers there says it is the state bird
The Ring necked Pheasant.
The state bird is the Ringed-Necked Pheasant. ^ ^ U
North Dakota's state bird is the Western Meadowlark. South Dakota's state bird is the ring-necked pheasant.
The American Pasque Flower is the state flower of South Dakota.The Pasque flower is known by many names. The Lakota name for the flower is "hosi cekpa" meaning "child's navel." Others refer to this flower as anemone, wind flower, blue anemone, Hartshorne plant, gosling plant, American pulstilla, prairie crocus, blue tulip, wild crocus, prairie smoke, sand flower, rock lily, headache plant, Coventry bells and the May Day flower.
The ring-necked pheasant was adopted in 1943 by an act of the state legislature. State Names, Seals, Flags and Symbols: A Historical Guide pp141-142
New Mexico (Roadrunner), Pennsylvania (Ruffed Grouse), Rhode Island (Rhode Island Red Chicken), South Dakota (Ring-necked Pheasant)
The South Dakota state bird is the common Pheasant.
Texas, Oklahoma, Kansas, Nebraska, Colorado,
North Dakota
The U.S. quarter coin with a commemorative South Dakota design depicts Mt. Rushmore, a pheasant, wheat, and the year of statehood. It shows a depiction of Mount Rushmore and the state bird, a pheasant wreathed by two heads of wheat. Any that you find in circulation are worth exactly 25 cents. There's more info at the link below.
The state of North Dakota is north (or above) the state of South Dakota.
The state of South Dakota is south of North Dakota.