I don’t know why they bark but I love howling with them.
The neighbour cat tortures my two girls. The cat will walk along the top of the fence, or sit outside of the closed gate, while the dogs go nuts! There is also a neighbourhood squirrel that does the same thing.
Whenever there is a siren or sirens (my neighbourhood it happens a lot!) and the girls are outside, they both start howling. The moment I open the door,dead silence. If they are inside and hear sirens, they ignore the sirens.
Funny thing, I live close by a glidepath to YYC and sometimes at night, one of the girls ‘warns me’ of an incoming aircraft by growling at it. Of course, ANY movement outside results in my girls exploding in barking. A rough neighbourhood, but I never worry if I forget to lock the doors when I leave.