Older dog becoming predatory?

[vacation1]

My brother has a bunch of dogs, and the oldest is a Cocker Spaniel who's probably about 12. Lately she's become very predatory toward small animals, killing squirrels and possums, whatever she can catch. A possum played dead in his yard and, as he said, she went over and made sure. Ew. It's the same place they've lived for about 10 years, a woodsy area where they sometimes get bears ripping apart the trash, deer in the yard, raccoons on the deck, etc., so it's not like she's never seen these animals before. I think he's a little worried about this development as he also owns cats and a mini Dachshund, so there's a chance the Cocker could hurt or kill some of the other pets.

Any ideas? As far as I know, she's not sick. She's not a particularly friendly or outgoing dog, but she's not aggressive toward people and up to this year, hasn't been aggressive to other animals.

[Bluey]

They may want to keep her confined and separated from the other pets when they are not around.
Run that dog by the vet, it may be something like low thyroid or something else, that causes sometimes changes in temperament, especially in older dogs.

[Casey09]

Predatory aggression can be strange, but I would say that it doesn't have much to do with aggression towards humans unless the dog is displaying predatory aggression towards humans (i.e. chasing bikers).
It does seem odd that this is a new behavior, and it can't hurt to ask the vet. However, I would think that aggression in response to a health problem would be more likely to be "cranky" aggression (i.e. in response to being touched in certain places, or in response to being woken from a deep sleep). To me, this is a whole different ballgame.
As far as the cat and the little dog, I do understand the concern. Some dogs display a lot of predatory aggression and are fine with their "own" inside cats, probably because they don't see them running the way that they see a squirrel or rabbit running. That said, it is something to watch out for, especially in situations where the cocker sees the other dog or cat running. It is the movement that is triggering this type of aggression. Perhaps the dog just had a successful experience with an animal outside and has become excited by it?