You had some opportunity here to go into more detail by using thinner lines. You could also have added some shading: for example, using the yellow to highlight the tan, or using the gray to shade the tan. My final piece of constructive criticism is that it's unclear what those black dots in the top left corner are, near the birds. If that was a mistake, it should probably have been removed, and if it was not a mistake, the placement probably could have been adjusted to make it a little clearer what those black spots are supposed to be.
