Kori Bustards (Ardeotis kori) are polygynous and males display singly or in loose lek formations to females during the breeding season. A new display, head tossing, has been observed on repeated occasions by five different males (all Ardeotis kori struthiunculus) in the Smithsonian National Zoological Park, Dallas Zoo, and San Diego Wild Animal Park. This display has not been reported for A. k. kori or in any other Ardeotis species. Trained behavior watchers recorded detailed observations of a male bustard's booming behavior and frequency in 2004 and 2005; over the 2 years they collected 407 hrs of booming data. Head tossing occurred when the male rapidly threw his head backward onto his back. The head tossing display further exposed the white neck feathers and the motion of head tossing was extremely visible. Head tossing was followed by a cessation of booming or was a transition between additional booming sessions. Head tossing primarily occurred at the end of a six-boom calling bout (90% of the time) and was observed infrequently (less than 2% of all booming bouts). Head tossing appears to occur predominantly during the early phases of the breeding cycle and may function as a territorial marker directed at other males, and potentially provides information about the rank of the displaying male.