From Muppet Wiki

A Security Guard stands outside Liberace's dressing room in The Muppet Show, episode 309, hired to keep out everybody but birds. Gonzo talks his way past him by claiming to be a turkey.

In an interview on Muppet Central, Steve Whitmire recalled, "The first time I ever did a speaking part, I was doing a guard that was outside Liberace’s dressing room door. Jim gave me this part to do, to try me in a speaking role, and I was terrible." Although Whitmire cites this as his first speaking role, he did perform Winky Pinkerton in episode 308 which was taped one week earlier. However, "speaking role" may depend on your point of view, as the character's lines are a set of bird impressions: "Cluck. Tweet-tweet. Cock-a-doodle doo."