Maybe we contain multitudes, and maybe we contain a couple great splashes of primary color. With one arm stretched high above his head, puppeteer Caroll Spinney has spent the last several decades embodying the warmest of yellows and grimiest of greens, playing — in every sense of the word — Sesame Street's biggest bird and most trash-talking grouch. Dave LaMattina and Chad Walker's I Am Big Bird offers just what the title promises, an involving and affectionate study of Spinney, whose fine-feathered friend we've all been following for almost half a century.

To become the bird, Spinney dons orange pants ringed with ribbons of pink and ending in three-toed feet that, through the genius of Muppet design, can't help but cheer you just by existing. How can bird feet stir such delight? Then Spinney squirms into a heavy, feathered, pear-shaped carapace from which he can see the world only on the monitor his scripts are taped next to. As he pilots this unwieldy creation, he is in a sense inside the egg, which might help him as he performs a feat more difficult than all the rest: connecting himself and that bird back to the real concerns of the just hatched. No actor has conveyed, with such emotional truth and over so long a career, the mind of a child — and Spinney does it while driving what is pretty much a parade float.

The Grouch is less of a feat, although hunkering down in a Children's Television Workshop trash can can't be good for the knees.

Occasionally the friends and colleagues assembled to toast Spinney in I Am Big Bird argue that Oscar is the yang to Spinney's sunny avian yin — that they're opposites contained within one complex man. A home-movie clip of Spinney, at a party, singing the Grouch's anthem “I Love Trash” suggests something simpler. Spinney's — and Oscar's — enthusiasm is just as heartening as Big Bird's, but the Grouch's love of garbage and his desire to spend time alone don't seem antithetical to the bird's wide-eyed sweetness. Big Bird is always just discovering the world, but that world turns Big Birds into Oscars — once out of the nest, we have to find our trash to love.

I Am Big Bird doesn't dig deep into Spinney, or Oscar, or Big Bird, or just why the man and his Muppets have been so resonant for generations. Instead it offers that resonance: Spinney in his bird suit on the set, at the Hollywood Bowl, at the Great Wall of China, sometimes in amateur footage that has gone touchingly soft-edged with age. Spinney years earlier, playing a bunny with Larry Harmon's Bozo the Clown. Spinney's wife, Debra, testifying to their love — and, in one quick clip, parading about in those bird pants. Spinney himself, tender and earnest, speaking of how tough it was to grow up as a boy named Caroll, and of his certainty, in the earliest days of Sesame Street, that he just wasn't a good enough puppeteer for the show.

There's one sublime tearjerker: Spinney, in the suit, singing “It's Not Easy Being Green” at Jim Henson's funeral. Henson, meanwhile, is best represented in the story of how Spinney first caught his eye — after Spinney's one-man stage puppet show went terribly wrong, Henson approached to say, “I like what you were trying to do.”

This sweet and moving film might be better if its creators more often pressed Spinney and company on its minor controversies: Sesame Street staffers imply that he can be moody and a little difficult, and that this improves the performances, but everyone's too polite to offer any details. A dust-up with Sesame Street director-producer John Stone is so vaguely recounted that it's not clear why the filmmakers bothered to include it. The same goes for some late-film material about Spinney's feelings regarding the ascent of Elmo, who has taken over as king of the Street.

I like what I Am Big Bird is trying to do — I just wish it were a little less Bird-nice, and a little more Grouch-frank.

I AM BIG BIRD | Directed by Dave LaMattina and Chad N. Walker | Tribeca Film | Music Hall, Playhouse

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