Nouns: my take on the current discussion.

I've read with interest the various conflicting opinions about when animal and plant names should have capital letters. There's actually no debate about this - it's quite straight forward:

If you are referring to a species it has a capital initial letter: if you're just talking about a type of living thing in general, it doesn't. This is not a matter of opinion, it is English grammar! Proper nouns have capital letters!
Here are some examples:

The African Lion is one of the few cats that live communally
Either side of the gate was the statue of a lion

He photographed a weasel on the back of a Green Woodpecker
Four species of woodpecker regularly occur in the UK

If you are using the Linnaean binomial classification, the genus has a capital initial, the species does not:

African Lion - Panthera leo
Green Woodpecker - Picus viridis

Again, this is not a debate topic, it's scientific convention!