On a whim, I modded the animal-person template to give all animalfolk the [pet] tag. I was expecting them to act like regular animals, or perhaps like tigermen used to. Instead, I got a bit of a surprise with my trained wrenfolk and bushtitfolk:
* They can be butchered, but the products won't be eaten, tanned, or even hauled, despite the fact that there are entries in the stockpile interface for them. The products also don't show up on the z-kitchen list and don't show up under 'meat' in the trading interface (haven't checked whether they turn up on search). I don't have a bonecrafting industry set up, but I expect that the bones won't be used for that, either. Eggs appear to be hauled as usual, though.
* They can be assigned to both pastures and burrows. I've confirmed that they respect burrow assignments; I believe that they respect pasture assignments, but I'm not sure what happens when they're assigned to both at the same time - their current assignment is an overlapping burrow and training-enabled pasture, just to be safe.
* They get thirsty, and will seek out water when they are. I suspect that they follow the same rules that dwarves do regarding thirst and burrows - I had a thirsty wren man in a burrow with a stagnant pool, and he declined to drink from it. I removed him from the burrow, and he went to the non-stagnant lake I'm embarked on and drank from the edge of that. I haven't checked on whether they'll use a well or not, and haven't tested whether they'll break their burrow or pasture assignments to drink.
* They get hungry, and seek out food. I've seen one (a wren) eat a fish-based roast. They appear to be able to take food from barrels.
* They get tired, and sleep. So far, they're sleeping on the ground in their area; I'm still putting rooms together for my dwarves but will be giving them some beds soon. It won't surprise me much if they can have rooms assigned to them.
* I think I saw one removing some construction - at least, he was in the right spot for it at the right time, even though it was well outside the burrow area and not someplace he would have been as a matter of course.
I've never kept tigermen, so I suppose I could be wrong about this being mostly new behavior, but I'm pretty sure tigerfolk care instructions were 'make sure they have water they can stand in to drink, and you're golden', and that's not what I'm seeing here at all.