per wiki :
The book "G" is for Growing: Thirty Years of Research on Children and Sesame Street refers to Big Bird as a canary. In an episode of Sesame Street, Big Bird was asked if he was related to the cassowary, he replied, "I'm more of a condor." On a 1976 episode of Hollywood Squares, he said he was a lark, causing host Peter Marshall to crack up. In the film Don't Eat the Pictures, Osiris calls Big Bird an ibis. Big Bird appeared in a series 11 episode of Mister Rogers' Neighborhood, in which he declares he is a "Golden Condor". Regardless he is always described as being flightless.