Exposing for silhouettes is tricky because you don’t know what percentage of the foreground versus the background is influencing the meter reading. In the case of the mountain goat you see here, if the meter was primarily responding to the animal’s bulk, the picture will be lighter because it is in shadow and the meter would try and make it middle gray -- as meters are programmed to do. If the meter was influenced mostly by the very bright background, the picture will be darker. This is why it’s impossible to predict what kind of exposure you’ll get. In a situation like this, do a test shot on Program mode (because this mode will give you a fast shutter speed) and then tweak the result (if need be) using the exposure compensation feature built into your camera until you get the look you want.
My settngs for this picture were 1/320 at f/16 and 200 ISO. I used a 24-105mm lens set to 100mm.