The Gambia is dissected by the river of the same name, in fact the country is just one long "sausage" either side of the river. Really you should try and fit in a river cruise while you're here. You get to see life along the various river villages, lots of birds, and if you are lucky you will see crocodiles and hippos. We did!
One of the highlights of our stay at Janjanbureh was the vast array of birds. Just around the lodge, along the river and on a walking tour, we saw many, many birds, such as this glossy starling. Unless you are a very experienced birder, it is always worth taking a good guide, both for spotting the birds and identifying them. A pair of binoculars are a must and if you wish to photograph them you will need a lens with at 500mm.