Why did medieval plague doctors wear strange beak masks ?

Why did medieval plague doctors wear strange beak masks?
During the Middle Ages, the plague constituted the greatest terror throughout the world, and was capable of killing hundreds of millions of people in waves that no one could stop.

During that period, we can say that the plague doctor was one of the most mysterious figures that appeared in that period.
Plague doctors were public servants hired by villages, towns, or cities when the plague struck. In theory, the primary duties of a plague doctor were to treat plague victims and bury the dead.

But there were many other tasks for plague doctors: they were responsible for tallying the number of victims in public record books, and documenting the last wishes of their patients.