For shadows duplicate your chicken (or whatever) and make it black (for ease of looking), put it behind your chicken. Using free transform, hold control and pull on the center top to side. Play with it and align so your black layer meets behind the feet. Now use the warp tool to bend it slightly (curve of sand), use a slight Gaussian blur to soften the edge. You can now also use mask to lower the opacity of the head area (since it is further back), but use a very soft low opacity brush or gradient map so it doesn't look harsh. Now for the important part. Control click on the black layer thumbnail and click off the eye. This leaves marching ants. Now select the sand layer and, using the brightness/contrast tool, move the brightness slider to the left to taste. Viola, more realistic shadow.