Hi,
I have noticed this behavior again by the male. These swans and ducks have been fed by people for years. However I believe they have been being fed by more and more people. Once they see a person they swim to land to get fed. Now the male will fluff up and chase the female off! I believe it is food aggresion oriented. Today when I got to the pond they both were all fluffed up and I was told someone just got through feeding them. About 5 minutes later he flew up and went across the road to forage in the ocean. He seems to trust female just gets very territorial/aggresive when humans are around. I try to stay hidden off in the street so he doesn't see me + get all wound up.