|This article is about an older version of DF.|
Pets are creatures that have been adopted by your dwarves. All creatures that can be tamed can be made into pets; that is, most creatures that are both non-sapient and non-evil. Pets will follow their owners around, providing a companionship happiness bonus (based on the creature's pet value), being fed by their owners if they are grazers, and, in many cases, protecting them from harm, either by actively attacking enemies or by acting as meat shields that allow their charges to scramble away to safety.
Pets cannot be assigned; rather, dwarves will adopt them on an ad hoc basis. (Except for trained hunting and war animals, which will be adopted by whomever they are assigned to.) Dwarves that are idling near a wandering stray animal may choose to make them their pet, giving them a name, causing the animal to follow them around, and giving the owner a happy "got a pet" thought. The chances of this event happening are strongly influenced by your dwarves' personal preferences; while they will rarely go out of their way to adopt animals, every dwarf has a preference for a certain creature, and will select them as pets when available, often resulting in the fortress engraver being followed around by a family of cavies.
You can control what animals are up for adoption through the animal status screen, the first tab on the menu. There you can toggle available/unavailable on each tame individual, freeing them up for adoption. Animals will never be adopted out of a cage, and must be let out to roam for adoption to take place. Stray animals tend to accumulate at meeting areas, which facilitates adoption. Make sure that your meeting areas are large enough to accommodate all your strays and prevent overcrowding, and be aware that grazing animals tend to starve to death in your dining room if you do not assign them to a pasture instead.
In the case of grazers, owners take care of feeding their pets.[Verify] details are fuzzy?
Cats are notable for being an exception to the rule; they will assign themselves to dwarves, and cannot be made available or unavailable. Vermin pets will perch on their masters' shoulders, protecting them from those darned cats.
Pets will provide a happiness bonus to their owner for the duration of their or their owner's lives. If the dwarf dies, the animal becomes a stray, and is available for adoption again. If the pet dies, the owner will get a negative thought, made worse if the pet isn't given a proper burial. This even happens if the pet dies peacefully, from old age.
As long as a creature is somebody's pet, they cannot be butchered, chained, or caged; this can lead to a catsplosion when there are several crazy old cat ladies in your fortress and you don't immediately butcher all the kittens. If you do manage to assign a pet to a cage or restraint (by issuing the order before the adoption), the new owner will attempt to release it. Newly acquired pets that were previously scheduled for butchering will still be butchered, however the new owner will experience a negative thought from the loss of their pet.
Another possible use is for large grazers, which are unable to keep themselves fed via grazing. By turning them into a pet, you can essentially have a dwarf dedicated to keeping them fed. This could open up some interesting options. (such as utilizing tame elephants without worrying about them starving themselves)
The value of a pet is based upon the species' internal pet value, a number in turn based on a number of factors: body size, exotic-ness, and intelligence being among them. It also helps if the animals in question aren't useful for anything else, although assigning pets to pastures to keep them in place works fine, allowing such thing as pet alligator egg farms. Milkable and shearable pets are excellent, since they can still be taken to a farmer's workshop to get their goods. The best pets of all are cave dragons and dragons, if the world is old enough and/or you are lucky enough to cage some.
Migrant waves will bring stray animals, but may also bring pets along. While this can be a boon, some players may find it a hindrance; animals with no value beyond butchery, such as pigs or cavies, may be viewed as clutter. If so, you can assign them to a pasture somewhere conveniently dangerous, such as under a atom smasher or in a field to trip up ambushers. Be warned that dead pets generate negative thoughts.