Validate uniquness of each animal.
Validate uniqueness of a region name.
Add flash messages and introduce partial for errors.
Add flash message and redirect inside the region controller.
Add ability to edit and update an animal.
Add ability to edit and update a region.
Introduce sighting class and validate presence of both region id and animal id.
Associate that a sighting belongs to both an animal and a region.
Create association that an animal has many sightings and that an animal has many regions through sightings.
Create association that a region has many sightings and has many animals through sightings.