As you know by now, Oh Student of Literature And Film, where a bird appears a symbol is never, ever far behind. And Birdman—a movie with a bird in the dang title—is no exception.
In the play-within-a-film, the character of Laura says the following line:
LAURA, PLAYED BY LAURA: There's a certain distance to it all now, a wistful distance, underscored by a gentle breeze and the sound of the birds, laughing at the whimsy of it all.
She's talking about Nick and the baby they didn't have. It just makes us think how awesome it would be to be a bird, flying high in the sky without a care in the world—except maybe hawks and helicopter blades. And, as in many works of art, birds in Birdman symbolize freedom and perspective—they have the ability to escape the mundanity of everyday life as they soar through the clouds.
But what about being a bird…man?
Birdman isn't your happy-go-lucky kinda bird that's up high enjoying the scenery; he's blowing things up for the people's delight, partaking in the suffering and triumph of the earth. Really, he's about as un-birdlike as you could get, from a symbolic perspective.
This is why, at the film's end, Riggan says goodbye to Birdman and opens the window to the birds flying blissfully outside in the wind.
We'll never find out what Sam sees as she looks out that window, but the tattoo of a feather with birds flying out of it on her left shoulder suggests that she also understands the beauty of flight.