I think being reborn as a tiger or any animals in the animal
kingdom is already bad karma, as it is in the lower realm.
being an animal, you either kill others for food or eaten up by
other animals. if you dun want to be reborn as an animal, pls do
not commit bad deeds. if you are reborn as an animal, its takes a
long time for you to be reborn as a human, as the birth of a human
is very rare, so do not take for granted that you will be reborn as
a human even if you do not commit any bad karma in this
lifetime.
once a buddha commented to his disciples on the mound of ants
beside a tree. the buddha said that these ants have been ants for
many aeons of time, since the first buddha stepped onto our world
has elapsed, they are still reborn as ants.