Colloquial term referring to a moose. Moose often browse in swamps and marshes, eating the tender water plants, hence the swamp reference.
The donkey part comes from the fact that they are an animal that is both tough and stubborn.
The man was well-prepared to spend a day in the forest, as he was confident that he would get to photograph a swamp donkey in its natural habitat.
The plural of moose, the North American Elk, (Alces alces)
Your hair is beautiful. It is not dissimilar in it's majesty to a herd of meese wafting across the tundra.