Most birds have a very poor sense of smell and rely much more on their other senses. A few, like vultures and some other birds of prey, have an excellent sense of smell. A vulture can smell prey from a distance of more than 1700 metres.
porschebabe, I think you might not understand how this site works. It is not a live chatroom and so when you post a question you might well have to wait a few days until you get some answers. Actually, you now have had three responses in one day which is pretty good.
Porschebabe, I didn't read your question properly before posting my previous answer. Suggest that you use your own sense of smell to check your nesting blackbirds. Seems very unlikely to me, unless they are dead and rotting in the nest.