Highly toxic...
MY first question would be what is the source of the smell are you trying to mask? Is the source related to the bird, like from bird poop? If this is the case you would need to take the bird to a vet, as smelly poop is indicative of illness.
oh, I posted before i saw the dead carcass post... you, should really try to locate the animal and remove it from the wall - open the wall or ceiling. You are faced with potential helath risks, swarms of flies, some dead animals are particularly foul smelling and the smell will get into clothes and ruin them...