We have seen this behavior in many swans. Some swans do not like having their cygnets out of their sight and once the cygnets are returned, the parents are not ready to accept that the cygnets are theirs. The longer the cygnets are away, the more aggressive the behavior.

If the swan parent sensed blood or an injury to the cygnets, he may have been trying to determine if they were injured enough to dispatch them, i.e., kill them. We have seen infanticide in swan parents as well as older swans who do not wish to have pesky siblings swimming around. Parents will kill an injured or sick cygnet to save the rest from predators following after a weak cygnet and then stalking the healthy brood. Also, a swan would rather kill their own cygnet than see a predator such as a human pick-up the cygnet. This is just nature. So, luckily, he took them back and everything is normal.

The mother swan is moving her feet because she is stirring up aquatic vegetation and possibly small frogs, fish larvae, etc., so that the food rises to the top of the water since the cygnets do not have long necks to turn upside down and reach the food supply. She stretches her neck after performing this ritual because she is either stretching or showing the triumphant sign that she has been successful in taking care of the young birds. The Regal Swan