Alma Mater was originally intended to be gilded, but never was. The bronze eventually oxidized and the statue was instead coated and sealed.
Rumor has it that back-up Alma Maters are kept at the ready should need arise. During the late 60's and early 70's, it seemed likely- in fact, Alma Mater was bombed in the spring of 1970. The New York Times of May 15, 1970 reports that " a bomb partially damaged the statue of Alma Mater at Columbia University" and "tore a hole in the side of the statue."
An owl is hidden in the folds of Alma Mater's robes. According to legend, the first student of each College class to find the owl would graduate Valedictorian and marry a Barnard woman (back when Columbia College was still all-male.)
Columbia's Alma Mater has a sister at the University of Havana. The Cuban Alma Mater was created in 1919 by Mario Korbel and inspired by Columbia's Alma Mater, while Korbel was residing in New York City. More recently, it served as somewhat uncanny validation for Bill O'Reilly's claim that Columbia is the "University of Havana North".