While at Campanario I saw white-face capuchins and howler monkeys (which of course were also heard howling). But this sleepy monkey was high in a tree and at the time I wasn't able to hang around and hope for a better look at it. So while Don asserts with British certitude that it is a howler, it sure looks like it only has 4 fingers which would make it a spider monkey. So, here is one to guess at.
Keith Christenson - Wildlife Biologist