If I take Hap to see a reported Canada Goose on the lake, his blood pressure rises and he immediately takes off after it. He'll swim a great lengths to reach it at which point it takes off or flies to another portion of the lake.
It is important to note that Border Collies don't immediately make geese leave. These aren't ferocious dogs that want to kill the bird as it's prey. In fact, they are trained not to hurt the birds and you can see them back off once they get close to the geese. Rather, Boarder Collies are herding dogs that are known for "their stare," that intimidates other animals. There is only one other animal capable of the "stare" and that's the wolf, itself. It's their ability to run and swim long distances (one Border Collie can work 3 square miles and 500 sheep) and then use the "stare" to move animals where they want them. In the case of geese, it can take up to 30 days of being harassed by a Border Collie to seek a new home. A Canada Goose looks at a Border Collie as a nuisance and ultimately decides it's not worth the hassle. The "stare" also resembles a wolf, an immediate threat to the geese, encouraging them to move on. This is why other dogs are not effective goose dogs. A dog like a Labrador Retriever, which might bark at the geese and bounce around in a playful nature, is not threat that a goose would take serious. For this reason, other species of dogs are not considered an immediate threat to a goose.
I digress. The main reason for this post was to point out how interesting it is that Hap differentiates between ducks and geese. Above, you can see the Mallards and Hap, who's after his ball in #2 pond, swimming in close quarters, all minding their own business.
If you're interested to learn a little more on the subject, click below for a NY Times piece on the subject: