This is possibly the most brilliantly weird thing about geese in general.
A rare species is more likely to mate with a really common species if there aren’t many other if its kind around.
Nest parasitism can also lead to hybridisation. Where a canada goose has laid an egg in a rarer goose species nest, eg a barnacle goose or a white fronted goose, the canada gosling will imprint on the adoptive mother and think it is a barnacle goose. When it grows up it will want to mate with other barnacle geese. And hybrid geese will be born. A lot of the time these are also fertile, which does nothing to help the rare species.