Endowments at Maine's colleges and universities have lost close to half a billion dollars in value as the economy and stock markets falter, forcing them to cut positions, freeze wages and delay construction projects. With investments tanking, Bowdoin, Colby and Bates colleges, which have the largest endowments, saw their funds fall a combined $373 million in the final months of 2008 — a drop of some 22 percent. And that doesn't include this year's continued slide in investment markets.