I have described this as a “screaming match” between two cats. It is more a yowling match. One of the cats is inside the home. That is the resident cat. He considers the home and the area around the home his territory or ‘home range’. Just outside the back door there appears to be a ginger tabby cat, looking in through the glass. This is the invading cat. He is invading the resident cat’s territory. This would normally result in a pre-fight stand-off with the kind of yowling you hear in the video; followed perhaps by a fight or chase.
Note: This is a video from another website. Sometimes they are deleted at source which stops them working on this site. If that has happened, I apologise but I have no control over it.
But the backdoor separates them so they are restricted to this typical domestic cat yowling call which happens when there is a face-off as a preliminary to a potential fight. Normally during this pre-fight phase one cat backs down and slinks away because neither party wants to genuinely fight. They don’t want to incur injuries. It is so much more efficient to yell at each other and see whether either party can psych out the other party to believe that they would lose the fight.
Domestic cats, just like wild cats, instinctively defend their territory. The typical feline behaviour of spraying urine on vertical objects within a territory and particularly on the boundary of a territory is a way of telling invading cats that this is their place. It is a calling card and the objective is to avoid clashes. In the domestic cat world, you sometimes see resident cats spraying urine on an object and then the invading cat re-spraying it as if to reclaim the territory. This is because their respective territories are overlapping and therefore there is constant competition for it.
The resident cat appears to be a blue British Shorthair, but I can’t be sure.
SOME MORE ON HOME RANGE: