Anecdotally, it seems that small dogs are yappier, more excitable and more aggressive, and genetic differences between breeds may be at play here. However, a 2010 survey of 1,276 dog owners in Austria found that the owners of smaller dogs may be at least partly to blame, as they tend to give their dogs less attention and be less consistent with obedience training.
Dogs are pack animals, and when their owners are not assertive enough, the dogs often assume the leadership role, resulting in louder, more aggressive behaviour.
Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.