... big birdie. Considering how Mars makes candy spontaneously appear from nowhere more than his pockets could possibly hold, the idea of a magical hat isn't entirely out of the question, but I don't think that's what he was going for there. I was imagining the birds a lot smaller than that. I'll have to change that. 

What if he put a loop of wire covered in his nen around its neck? He would be the type to take a bird for a walk... in an airship, and that would actually help him get unlost if he just let the bird lead him. I'm not sure how a nen-beast would react to something like that though.