SOME FUCKER SAID PLAGUE AND PLAGUE DOCTOR
Ya the bird design was very much a deliberate choice based upon medical believes of the time. The idea that birds carried the plague the idea was to both draw it from the patient as well as scare it from them also.
This was also why they often had tinted lenses too as they also thought plague could be communicated throw nasty/dirty looks and it served as another means of protection.
The very image of the plague doctor was also visual communication. Often communities didnt know plague was in their midst until a Plague Doctor was spotted. It also made them much easier to visually recognize and avoid.
The Rose-Clad Demon Doctor 