I am not an expert but I have been chatting to someone who is about nature photography recently. I was told that it is best to shoot on full aperture and focus on the eyes. That way the background gets thrown out of focus and all emphasis is on the subject. The exception of course is if you want to show some habitat. Richard.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html