Why didn't Blu learn to speak human?
- Birds can pronounce human words so he can't use being anatomically different as an excuse.
- They can pronounce them, but they don't understand them (with extremely rare exceptions like certain African Greys). They just treat human words like odd-sounding flock calls. That Blu can't understand human talk is actually a bit of Fridge Brilliance. Besides all that - Blu and Linda understand each other just fine, human talk or none.
Why didn't Tulio threaten Linda with legal action in order to get Blu?
- It's understandable why he wouldn't want to, being a nice guy and all, but it can't be legal for Linda to own such a rare bird. Plus, you would think she would need some sort of license to own Blu, which, given that Blu literally fell off a truck she probably doesn't have.
- You answered your own question - It would be out-of-character for him to do so.
- There's also a huge pile of practical and ethical problems with taking birds that bond tightly to their owners (like macaws) and throwing them bodily into unknown situations - the stress alone can kill them. Blu was raised by Linda from hatchlinghood. He'd have to be gradually acclimated to free-living, which actually happens over the course of the movie.
Why did Tulio fly all the way to Minnesota to ask Linda if she was willing to breed Blu?
- Wouldn't it have been easier to just shoot her an email?
- Maybe he wants to see the bird in person? In order for the breeding to work, he obviously has to make sure Blu is of the same species, and being such a Nice Guy (and a bit of a bird fanatic, as is shown), he probably sees it as more appropriate for him to fly to Minnesota in order to identify him completely, rather than have Linda spend a lot of her time and patience flying to Brazil to meet him, only to find out that Blu wasn't the kind of bird they were looking for.
How did Linda keep Blu for 15 years without anyone telling her what species he is and/or contacting her about it?
- You couldn't possibly say they've never been to a vet before.