A Native in Arthur Ransome's Swallows and Amazons series is a person who is not a member of a crew of sailors, explorers or pirates.
Natives may be adults, relatives or unknown members of the public. All are 'out' of the 'in-group' but natives can be well-regarded (the best of all natives) or enemies (unfriendly natives). In wintertime, the natives tend to wear fur coats and other heavy clothing, and are therefore called "Eskimos". Natives are to be blame for many unneccesary objects and activities such as highways, garbage and noise, but are also the source of civilization (ice cream), which Roger finds important.
The term native may also mean 'associated with worldly concerns' (as opposed to camping , sailing and having fun).
Susan's preoccupations with food preparation and hygiene are often considered native; Captain Nancy thinks (about staying overnight in the Fram) that Susan, she knew, was always a little inclined to take a native view (WH20).
But when Mate Susan says They can’t start with nothing to eat after bathing she is overruled by the captain (Jim Brading) (WD6). Likewise when Dot says Let’s eat them before sailing Dick says Better while we’re sailing (PM16). After they reach the North Pole Dot suddenly decides that We must leave the Pole at once because they had not told the Dixons where they were going or that they could be late. Dick objects because they have signalled to the others; but not because they are safe in a shelter and a wintry night in a blizzard is not the time to start the return trek! And they are probably wet through (WH28).
Bill of the Death and Glories is said to sometimes have a "native" demeanour like Susan.