To participate, you simply need to register at the link at the top of the ChicagoWildlifeWatch site, and then click the Classify button. You'll be shown images on the left, and asked to identify the creatures you see by picking from a list on the right. You will also be asked how many you see, and what sort of behaviour they might be displaying (e.g., head up, head down). If you're not sure you could tell a grey squirrel from a flying squirrel, don't panic: the same images will be shown to all participants several times, so misidentifications will be weeded out via redundancy. Do take your time, though, because the animals are sometimes hard to spot against the background.