A West Australian man has shared photos of his surprising discovery of a baby bandicoot sheltering beneath a nesting duck.

Mandurah resident Rex said he was checking on his pet duck’s eggs last week when he found the little marsupial huddling among them.

"I thought 'what are you doing there?'" he told WA Today.

While the mother dig did not appear to be overly bothered by this uninvited guest, she was eager to return to sitting on her clutch, prompting Rex to restore her to her position on the nest.

A short time later, the eggs hatched but the bandicoot remained – a fact that remains unchanged five days later.

The mother duck seemed largely unfazed by the bandicoot's presence among her ducklings. (Wayne Cuthbert)

Rex said the infant has not left the shelter of the mother duck’s underside, save for a few occasions.

He believes the bandicoot’s continued health suggests the baby has not been abandoned but has in fact been returning to his mother for intervals of time.

He said the marsupials – which usually eat insects, grubs, berries and fungi – regularly steal feed left out for his chickens.

Infant bandicoots typically dwell in their mother’s pouch after birth and are reliant upon milk for nourishment.

Eventually they emerge from the pouch to forage on their own, and after about three months become independent of their mothers.