One family of animals I admire for both their beauty and for something we, humans, are not able to do: birds!
Bird are able to fly (except for ratites of course). So caged birds I always think sad. While watching birds fly in the wild always makes me smile and provides a sense of freedom.
This great flying tern stamp I received from South Africa.
By the way, a flying tern is in the logo of the international bird protection organization Bird Life, and also in the logos of several partners, among them the Dutch and South African bird protection NGO's.

Love the way the stamp has been postmarked across. As if it is to show how high a bird can fly :-)
The following stamps show the contrast between a caged bird and birds in the wild:

Well, the caged bird isn't on a stamp himself, but is part of a larger stamp sheet, of which the stamp shows an other freely flying species.
The godwit (grutto in Dutch) is a bird who thrives in the grass-land. Grass-land birds have been, and still are, threatened by intensive farming in our densely populated country. Fortunately there are several initiatives to help farmers combine farming with nature protection (but still it's not enough, I am afraid).
Other flying birds are these wild ducks, beautifully pictured on a Finnish stamp. This bird is common in many countries.

To my pleasure I see that both Violet Sky and Joy have posted Australian stamps. In Australia some of my all-time favourite animals are liviung: the echidna, the platypus, the kookaburra, the cassowary and the brushturkey. The last-mentioned I've never seen on a stamp, the others I did see.
Among them this kookaburra:

And, my favourite stamp (which I fortunately received more than once!), the platypus:

Some other wild life, tiny ones:

However, the words 'Animals in the wild' will make most people think of larger animals, mammals to be specific.
Animals in forests and nature reserves, from Belarus, Russia, Canada, Germany and the Netherlands (the latter is a personalized stamp, temporary issued by natuurlijkefoto.nl):





Wild animals like elephants....

... and lions (this is from a stamp sheet showing more animals, that is, silhouets):

And arctic animals, alas endangered, too:

Check Sunday Stamps for more animals-in-the-wild stamps!