That's right: From June 3 to July 2, there'll be a post each day highlighting Teenage Mutant Ninja Turtles canon immigrants. Now, because TMNT canon is a little confusing, it can be hard to tell what counts as a canon immigrant and what doesn't. So for the purposes of this blog, a TMNT canon immigrant is anything (a) from the movies, cartoons, video games, toy lines, or tie-in comic series that later appeared in (b) TMNT volumes 1, 2, or 4 [because they're by the original creators] or TMNT volume 5 [because the original creators are involved, it's the new official continuity, and its goal is to use as much of the diverse TMNT lore as possible].
I don't know if this is where I should start, but it's where I'm going to start: in the 80s cartoon episode "What's Michelangelo Good For?" (October 1990), Michelangelo has a pet pigeon named Pete. Pete, however, is just a normal pigeon.
In the 2012 series, a mutated pigeon named Pete appeared in the episode "The Gauntlet" (November 2012) to help April rescue her father. He later joined the Mighty Mutanimals. I have no idea if he's named after the above Pete, but he probably is.
Pete later appeared in the IDW series as Old Hob's first attempt at creating a mutant. It did not go well, and this version has more criminal tendencies than the Nick cartoon version. He first appeared in Teenage Mutant Ninja Turtles #35 (June 2014), and later joined the Mighty Mutanimals as well.