In the 17th century, these masks were worn by doctors going to see patients who had the plague. It was believed then that sickness were caused by bad smells. The beak was stuffed with herbs purportedly believed to help ward off the maisma of the plague. 
Read more here:

In the 17th century, these masks were worn by doctors going to see patients who had the plague. It was believed then that sickness were caused by bad smells. The beak was stuffed with herbs purportedly believed to help ward off the maisma of the plague. 
Read more here: https://theconversation.com/a-brief-history-of-masks-from-the-17th-century-plague-to-the-ongoing-coronavirus-pandemic-142959