Mute Swans are monogamous and mate for life. However, when one of a pair dies, the other will try to find another mate. A male will then find a younger or older female, but a female will look for a younger male.
Yesterday, I went to Glades Wildlife Refuge at the southern end of New Jersey not very far from the Delaware Bay. On a pond there, a bevy of Mute Swans was foraging for food, each swan separate from the others, except for a couple. Unless I am mistaken, a smaller female and a younger male where going through courtship rituals. Young male swans have a dull gray bill that will become orange in color when they are mature.