We all know that Oscar's voice was inspired by a cab driver who drove Caroll to the original SST studio when he first came to New York, but has anyone else besides me noticed that in the earlier seasons of the show, Oscar also seemed to go back and forth in having a sort of Tony Danza-esque New York accent and not having an accent at all?
I was just thinking about this the other day. He did really seem to go back and fourth with the accent. In later years it seems to be gone almost entirely, except for a few words, occasionally, like when he says
"What d'ya got the-ya (there)" (Sorry, it's hard to type a New York accent)
I noticed, Eric Jacobson seems to have added the New York accent back, just slightly.
I've also noticed that from Episode 1 and throughout the 70s, Big Bird would often bob his head when he would walk, much like a number of species of real birds do. These are subtle little nuances that Caroll gave the characters, but it kind of makes me wonder why he eventually dropped them.
My guess is just that your arm tires more quickly when you add subtle movements like that. Big Bird did seem to get a bit stiffer in the 90s, though i'm not sure if that's due to Caroll's age or because the character seems to have gotten older and more mature, and therefore less plucky and energetic.