"The mama duck unfortunately died after the young ducklings were born. The mama duck’s best friend, a white Akita dog, decided to take over the role of a mother. The ducklings have bonded with the dog and they have become inseparable ever since.
I see it could be two ways. One: the big dog is very kind and left the big bed for the pup. Two: the pup went on the big bed and left the small bed for the big dog. In that case, if I was the big dog, I would just lay on the small dog (or around it).