Hell of a thing to ID a small mammal from a head only photo as far away as this one! (No photo of the tail, pads on the hind feet, or views from different angles. Ears blurry. Only rough indication of size by comparison with plant leaves etc.) But so far as we know, there are only two real contenders - juvenile Black Rat (R. rattus) and House Mouse (Mus musculus). (For example there is no New Holland Mouse there as far as we know.) And of those two I think probably the former. But this is only a tentative ID.