If you summon a pet with the Owner tag it will belong to that owner. Ex:
/summon Minecraft:parrot ~ ~ ~ {Owner:Notch}.
However, If you try to change the pets owner with the /entitydata command, it does not work. Ex:
/entitydata @e[type=Parrot,r=5] {Owner:Jeb}.
The pet will continue to belong to the original player it was summoned with.
Unfortunately changing these tags is unsupported.
https://bugs.mojang.com/browse/MC-66943?focusedCommentId=188032#comment-188032