While searching for a new litter/bedding for the birdcage I saw this in the comments of bird site and thought it was good to know.
"The investigation found that aspergillus spores occur naturally in newspapers at safe levels until they hit the age of 2 weeks. Then the number of spores found in newspapers starts to increase exponentially with the age of the newspaper. The implications of this have led to Australian Wildlife Carers being taught to only use ‘new’ newspapers to line cages and enclosures."