You can always do backstitching if you want to make the animals stand out. I've done this on most of my projects, even if the pattern doesn't call for it. I think it looks better with black backstitching or other dark color (black/brown #3371, navy blue #938) to make a distinction between all of the colors.
I've shown some of my work to friends before I've backstitched and afterwards. They say it looks better with the backstitching. The colors seem to "pop" out at you with the backstitching done.
As the saying goes, the devil is in the details. When I have all of the require cross stitching done, then I say I have the detail work to do before it's finished.
Backstitching is more work to do, but I think you'll have a nicer looking picture in the end.
Diana