When sketching outdoors a method I sometimes use is to make a sketch firstly with an ink pen and then complete the picture by adding watercolour washes. I find this helpful to quickly add colour without getting bogged down in if its exactly the correct tone or shade. This is also a good method for adding smaller detail by pen and thus eliminating the need to carry a rigger or other small brushes in your sketching kit.
Although the scene above is void of any animals this doesn't prevent the artist from adding some life into the studio picture at a later date, after all this is what sketches are for to collate information to produce a final pictures from. Usually there would be a flock of sheep in the foreground field however none were present at the time (sheep can sometimes be shy). It would be a good idea to add a few sheep grazing in the foreground possibly looking in towards the dirt track leading to the main gate. I would probably also add a cloud shadow across the near foreground to give the picture a greater sense of depth. That's the beauty of artistic licence, you can make the scene what ever you like although I would restrain from adding any wildlife which wasn't native to the Yorkshire Dales.