A suggestion for all of us who love wildlife, often (and justifiably) more so than human beings: if you witness abhorrent behavior such as outlined in so many comments in this thread, please take a moment to contact the state/province wildlife office nearest to you, as soon as possible, and report the incident. While laws vary from one state/province to the other, most have very strict laws against harassing wildlife. In Colorado, for example, dogs chasing deer--or any wildlife--can be lawfully killled for doing so. A quote from a Colorado Parks & Wildlife regional manager: "Pet owners should know that, because it is so harmful to wildlife, any law enforcement officer in Colorado is authorized by state statute to use whatever force is necessary to stop any dog that is chasing, injuring or killing a wild animal.” He went on to encourage anyone who sees such behavior to contact Colorado Parks & Wildlife or the State Patrol. The penalties against harassing any wildlife, by two- or four-legged creatures, are usually quite severe; at least they are in Colorado.
Point being, witnessing bad behavior and doing nothing about it does not stop the problem, nor does it stop the offenders. Many people think of their state or federal "game wardens" as only being concerned with unethical hunters; in reality, problems with the public at large occupy most of the officers' time. So, we will all be doing the wildlife a favor by reporting unacceptable and harmful behavior to the authorities.
An interesting side note: at least in Colorado, wildlife officers have more power and more authority than the police; in fact, more than just about any other law enforcement officer. And they take their jobs seriously. The Federal wildlife officers I've spoken with are even more zealous in their enforcement. They have no sense of humor when it comes to wildlife violations. So, take a moment to report the offenders. The animals and the birds will thank you.
