A few years ago we lived in a house where there was a stream at the end of the garden. At the time we had four cats who formed a loose tribe under the supervision of the big matriarch, but mostly drifted about doing their own thing. They were the most domesticated,suburban, bourgois set of creatures you could ever meet.
One early morning went down the garden and three of them were standing, literally shoulder to shoulder on top of the stream bank, glaring across the water, Parkin, the matriarch, was by the side of the stream in full battle mode, making that noise that is the cat equivalent of "Come and have a go if you think you're hard enough!"
Behind her, were a duck and six ducklings.
On the other side of the stream was a big, very nervous looking fox, which dashed away when it saw me.
The cats treated the ducks that nested on the bank as part of the household, so they never touched them. You would even find Charlie, the smallest cat, curled up by the stream with the ducklings all around him.
I've never seen cats co-operate to face down an intruder before, andcthe idea of them defending other domestic animals is amazing to me.
Cheers
Dave