These dogs are known to be very energetic and alert. That might contribute to their aggressiveness towards strangers.
Like other small dogs in the University of Helsinki's research, miniature poodles behave aggressively to make up for their size.
A smaller version of the standard schnauzer. Miniature schnauzers were bred in Germany in the 19th century as guard dogs.
These jobs help them burn off all their energy. Without enough stimulation, they can turn their liveliness towards aggression.
These medium-sized dogs, known for their woolly curls, were originally bred to retrieve downed waterfowl.
The curly-coated Lagotto Romagnolo breed began as a truffle-hunting dog in northeastern Italy.
Owners can take advantage of that trait and teach them tricks. This burns off energy and manages their aggressive dispositions.
These small dogs have poofy coats and a reputation for yapping. They're devoted to their owners, but very distrustful of strangers.