From Muppet Wiki

Hillary the Owl was a blue-gray owl who appeared as a guest animal in The Animal Show episode "Owl & Octopus

The puppet was recycled as a nameless owl in Episode 302: Crab & Snail, where it was interviewed by Rhonda Rat, and as Timothy the Owl (played by Bill Barretta) in Episode 303: Owl & Frog.

The owl puppet also appeared in Mr. Willowby's Christmas Tree and The Muppets' Wizard of Oz.