Why is this goose rearranging a swan nest?


I saw this greylag on a swan nest. It was moving sticks around, making the nest smaller in diameter and covering the eggs. It also occasionally sat on the eggs before they were covered. The swans were nearby but totally disregarded the best even though one was nesting on it just a day ago. What was happening? Why did the swans not care? Why was a goose moving sticks around a swan nest? It wasn't aggressive, and it's mate was looking but not involved.