For many good reasons Yorkies are often depicted as pooches with a "big personality in a tiny package." For starters, they're terriers at heart, which makes them feisty, energetic dogs. Secondly, because of their past as ratters, they were bred to work independently and can sometimes be suspicious of strangers. Lastly, they seem to forget about their size, which puts them in risky situations especially when they pick fights with larger dogs. Despite these attributes, be gentle; Yorkies have a soft side too.
Feeling Under the Weather
Virtually any condition known for causing pain or increased irritability can lead to aggression. For instance, a painful ear infection may cause your Yorkie to object strongly to being handled or touched on the head. Yorkshire terriers are prone to hypothyroidism, a medical condition that among several symptoms, might cause dogs to display an increase in aggression. It's always best to see the vet to rule out pain-induced aggression and other medical problems.
Practice Makes Perfect
As a general rule of thumb, the more an unwanted behavior is rehearsed, the more it puts down roots and becomes established. If your Yorkie recently has started barking at your neighbor or growling when you move him off the bed, you'll need to limit his exposure to such situations. So no more exposure to your neighbor and no more bed privileges -- at least for now. Although limiting your Yorkie's exposure to such situations won't help him get better, at least, you're preventing the behavior from becoming stronger and more difficult to overcome.
Change the Emotions
Whether your Yorkie gets upset when seeing other people or dogs or turns into Dogzilla when you must give him a bath, you may want to change his emotions gradually. Desensitization, along with counter-conditioning, aims to do just that. For example, if every time your Yorkie sees another dog or strangers, he gets yummy treats, with time, his emotional response will change for the better. Because behavior modification takes skill, good timing and the implementation of important safety measures, it's best to consult with a behavior professional.
Train Alternate Behaviors
Yorkies are intelligent dogs who are receptive to training when you make it worthwhile. Train your Yorkie to perform an alternate, incompatible behavior when he notices a trigger and reward him for utilizing this default behavior. For instance, if your Yorkie barks at other dogs on walks, train him to stick by your side and look up at you adoringly while the other dog passes by. Reward him for doing so. This may be difficult if the other dog is too close. Find a distance where your Yorkie is more responsive, or better, ask a trainer for advice on how to work under threshold.
Avoid Small Dog Syndrome
Yorkies, like other small dogs, are often prone to developing problem behaviors because of their small size. Dog owners often close an eye to their behaviors because they think they're cute or their Yorkies can do only so much harm. This is a big mistake. Like any dog, Yorkies should receive extensive socialization and training and need guidance as to what he can and cannot do. Starting at an early age will lower the chances for fear, aggression or frustration, so your Yorkie can start on the right foot.