I have 2 girls. When they are together, they will bark at any noise from outside. We live in the country so there are never any people around, as well as no cars driving by. When our outside big dogs bark, my girls usually will back them up from the inside.
But, when they are seperated, neither one barks very much...just rarely. I take Chewy to work with me, and Sierra stays home with my hubby. So, go figure. When they are together, it's like they are braver, and say to each other...don't worry, I got your back.....lol