There could be a couple of reasons for this scenario. Swans are not AGGRESSIVE, but rather DEFENSIVE. This means that they aren't just going out of their way to accost someone or something. They defend their territory, nests, cygnets and mates rigorously. If there were three swans, there is a possibility that one of the swans was a juvenile or cygnet. The swan that chased you was probably a male.

Now, the reasons:

1. Someone may have let their dog chase the swans. Unfortunately, this occurs more than one might think. Most responsible dog owners like yourself, keep their pets on a lead or under voice control. The dogs are not allowed to engage or chase the swans. However, there are pet owners that think it is funny to release the dog and even egg it on to chase or attack the swan. The swan may have been chased by a dog and thought that you were going to release your dog.

2. The swan felt threatened by an animal in close proximity to its cygnet or juvenile swan. The best way to counter the threat was to meet it head on and chase you and your animal from the area. Hopefully, this situation will not arise again, but swans with families will always be protective.

3. The swan was not chased by a dog or threatened by your dog. It may have been your young nephew. There are human parents just as bad as bad pet parents and do not keep their children under control. We have seen parents allow their children to throw rocks at stones, even going so far as to tell the child how to aim for the bird's head. The swan may have been chased, teased, pummeled with rocks or stones or generally harassed by a child. So, the swan is now in protective mode whenever it sees a child. The Regal Swan