This is near the Amphibian Pond and is one of two nests constructed close together. Red squirrels will do that, as will greys, and use one or both or neither. There is also a nest box nearby that has long been used by squirrels. The nests are near a large walnut tree overlooking the pond and several generations of squirrels have been occupying this territory. Of course, it may not be generations of the same family! Just as likely that one squirrel dies and another moves in to what would be, in squirrel terms, prime real estate!