From Muppet Wiki

The Evolution of Big Bird (1969-present)

Image	As seen in	Year	Notes
	Sesame Street Season 1	1969-1970	The original Big Bird is ungainly in design and characterization, with clumsy body movements and a hick-like voice. The arrangemnent of the feathers appears more haphazard. At times, he sports googly pupils, similar to the ones of Cookie Monster. Caroll Spinney has been quoted saying, "He didn't look too keen. I thought he was one of the ugliest things I'd ever seen!"
	Sesame Street Season 2	1970-1980s	More feathers are added to Big Bird's head, making him his current 8'2" size. His feathers are more groomed. Somewhere inbetween 1970 and 1980 his googly pupils are replaced by fixed ones.
	The Muppet Show	1979-1991	Big Bird is redesigned a bit, with a newer head, making him more resemble the current version.
	Sesame Street	1991-present
Alternate Big Bird Puppets and Characters
	The Blue Bird of Happiness	1985	A blue version of Big Bird with clown pants from Follow that Bird.
	Big Bird	2002-present	This is Matt Vogel's Big Bird puppet. The feathers on his head are fluffier, and his blue stripes on the eyelids are a slightly different color to not interfere with the blue-screen background used during the Journey to Ernie segments.
	Baby Big Bird	2006	Baby Big Bird as seen in Sesame Beginnings.