For comparison with its cousin, the Black Guan, check the following: http://www.pbase.com/hankvv/image/109795963
I only just saw one of these. It was at our hotel at Arenal Lake. I was out shooting Hummingbirds when all of a sudden this large bird came swooping in. It seemed to land some distance away in behind some trees/shrubs. I slowly made my way out to where I thought it might have landed and there it was eating fallen apples below an apple tree. At first I thought it was a Turkey Vulture. I got in about a dozen shots or so before it took off again.