"We expected it to be still there but it had gone."
Mollymawks are in the albatross family, spending their lives at sea "on big oceans and enjoying big winds". The bird weighs about 4kg typically with a wingspan of between 2.2m-2.5m.
Mr Campbell said they are a handsome bird. "They look really sharp if you get them in hand."
This one looked in good nick for its experience and didn't appear to be injured.
The birds are found around the Auckland Islands and other sub-Antarctic spots but are also seen in New Zealand waters, though not inland. Their conservation status is "declining".
"It's a real treat to see it," Mr Campbell said of the photographs the Sorensen family took of their visitor.