I am looking for opinions or experience with a dog that I am potentially going to adopt from a rescue group.
Basically I was told by the foster person that the dog regularly kills birds and ducks, and I have 2 cats. The foster has a cat but told me that the cat didn't like this dog, so she is having her cat stay with a friend while she fosters this dog (a large American bulldog).

Should I worry that this dog will try to kill my cats? If it kills birds regularly, can I just assume that it is going to be aggressive towards any smaller animals? I was told that the dog can be tested with a cat that the rescue group has (that is fast enough to escape any dog, which is why it is often used to test new rescue dogs' reaction to cats). I'm just very scared that, even if this dog gets along with that cat, it may (given the chance or left unsupervised for a few minutes) try to kill one of my cats.
Has anyone ever had a dog that killed birds and ducks, but showed no aggression towards cats? This dog is very people-friendly, and apparently gets along well with other bulldog-breeds (like my dog). I'm obviously seriously concerned though, and looking for advice or experience with this issue.