This is bad advice because most any cat (much less a dog over 10 lbs) could kill a ferret if they wanted to. Yeah, ferrets have big sharp teeth and are predators (of very small animals), but they weigh 2-4 lbs, can’t move very fast, are low to the ground and have delicate spines. My 70-lb dog could kill one with his front feet in two seconds, and my 20-lb dog would only need to get one good shake in. 5-lb creatures are no challenge to her terrier killing style. Biting back just makes her more aggressive. I’ve sat other people ferrets before and she definitely has a very strong prey drive towards ferrets - I would never in a million years leave her unsupervised with one.
Not that they can’t get along, but I wouldn’t feel at all confident introducing a ferret to a strange dog or cat, any more than I would introducing a 3-lb chihuahua. Small creatures are most likely to arouse the prey instinct. My killer dog exhibits clear stalking behavior even with small dogs, especially puppies - this is why she is not allowed in the ‘toy’ area at the dog park…
I find it amusing that at 5:30 someone admonished the bird not to hurt the dog - normally you wouldn’t think a Rottweiler would need protection from a bird, right? Of course, cockatoos do have an extremely powerful bite.
It very much depends on the dog or cat. Our English Setter had very little in the way of predatory instincts, and wouldn’t attack anything larger than a spider. Didn’t require any training when the chickens started coming into the garden, or with the neighbour’s cat. Showed a lot of interest when an abandoned baby starling was brought into the house, especially when it was being given flying lessons, but only wanted to sniff, not bite. She did catch up with a rabbit in the field once, but all she did was run alongside and muzzle it, until it disappeared into a hole.
A terrier would be a completely different matter, they were bred to hunt small animals.
We can call our dogs off rabbits and squirrels in the yard (squirrels are harder), and they’ve never given our other pets much trouble (we have a cat and used to have rats), but I wouldn’t trust our Australian Shepherd alone with a bird for a second, even though I’ve never had one. It’s just a hunch, but I still wouldn’t.
My dog (a larger than usual Jack Russel) was approximately 10 times the size of the cat when we got the cat. They’ve played together like best buds from day one. They were both young at the time - dog 6 months, cat 8 weeks - and that makes the main difference, I think.
We also look after an elderly retriever cross that is, if anything, disappointed she can’t play with the cat more because the size difference is too much; the two dogs play together, with the Big Dog’s tail wagging constantly, and the cat jumps along behind trying to get the tail. All three sometimes cuddle up to sleep.
Big Dog was also fine with our budgies, when we had them. They’d fly down right in front of her face and sometimes she’d sleepily paw at them when the feathers tickled her, then they’d fly away, but there was no hunting behaviour. Going on her behaviour with other animals, Big Dog is do docile she’d probably be fine with a gerbil trying to mate with her. So temperament makes a big difference too.
I think this has a lot to do with it, and the fact that most smaller pets are caged (i.e. given a “den” in the home). Both things set your small pet apart from intruders that might wander into the home like mice. We’ve had cats share our home with ferrets and rabbits, and it didn’t take them very long at all to realize they were off-limits, even though the current bunny was only 1lb when we got him, and not much larger than the squirrels cats usually have no qualms about going after.
You do wonder what that cat might do if it actually catches a squirrel. My dad has a cat that ended up playing with a wild squirrel. She would chase the squirrel, and if she caught up would back off. If she lost interest, the squirrel would run over and chase the cat.
When we had outdoor cats they enjoyed killing squirrels and chipmunks. And moles, and voles, and shrews…never any of those song birds people wring their hands over, though, unless bluejays count.