There are several possibilities to what is occurring with the "migration". Sam may have found a better food source, i.e., aquatic grasses, grazing grasses and vegetation nearby the second pond. Since it is a smaller pond, the vegetation may be more accessible and/or the banks are easier to navigate for the cygnets.

Are the banks at your pond steep? Has there been a drought that has caused the banks to become steep in certain areas?

Predators may also be a concern for the birds. If there are not enough secure hiding, resting, preening or nesting areas away from people, pets, and other perceived predators, the birds may opt for a quieter safer location.

Not feeding the swans at the other house may help the situation, but if there is an adequate optional food source (aquatic vegetation and material), then the swans may be more interested in this non-human provided food.

This situation can only be rectified by the swans unless you physically capture them, bring them back to your pond and seal the area so that they cannot leave the area. Just bringing them back will not fix the problem. They can still wander if the area is not fenced.

This behavior may also be a "migration" for the swans. Since they cannot fly, they are looking for a different area to raise their cygnets. Once the cygnets are grown, the cygnets will probably be left at this pond or yours so that the parents can once again have a pond by themselves.

Also, Black Swans have two clutches a year. So, once this group of cygnets are approximately 6 months of age, they will have another clutch around late summer, early fall.

Then, the problem will be what to do with the cygnets. Most state laws have clauses regarding feral populations and the cygnets will need to be pinioned before 3 weeks of age, so you are going to have to capture the cygnets and get them pinioned shortly. This may allow you time to bring them back to your lake and see how they fare. Then, you will need to find a home for the cygnets unless your lake is adequate to house two clutches per year. Otherwise, you will be overrun by swans which will become territorial, fighting and chasing each other from your pond. We hope this information is of benefit. The Regal Swan