What exactly are academic librarians?
At many (but by no means all) universities in the US and Canada, professional librarians (usually with a terminal Master's of Library Science degree or perhaps a PhD in some academic discipline) are treated as members of the faculty, including eligibility for tenure, participation in shared governance, etc. 

In many other universities, librarians are staff members and not considered part of the faculty.  In a few places, there is a mixture with some librarians on the tenure track and other librarians who might have an MLS degree who are strictly staff members.  Most libraries also have lots of support staff and student employees who aren't professional librarians.  

In places where librarians are considered faculty, they are usually expected to be involved in some kind of scholarly (research) activity and in teaching students.  For example, a librarian who specializes in archival collections might produce a catalog of a special archive and publish it.  Librarians often teach courses in how to use the library to do research and might be involved in teaching courses in library science to future librarians.