Depending on the voltage of the camera and whatever speaker you want to add, you might be able to avoid needing another PoE line by using a splitter, as described in this post:
As anyone used an ethernet splitter on one port for two cameras?
ipcamtalk.com
However, it might be far easier just to get a camera that already has a speaker, however, it might not be loud enough to scare a bear... most cameras that have speakers I have seen are not very loud. So, a splitter for a dedicated speaker might work better. However, then you have to consider how you are interfacing with the speaker, through
Blueiris, or some other app. I have never added an external speaker but I am curious to follow this post to see if others have more info or experience.