[Boromir88]

a) he was not actually much active (from what we know), he was just fond of beasts and plants~Legate

Interesting you say this, as I think you have a point. Also from Hammond and Scull's LOTR Companion Tolkien writes:

'it is clear that Gandalf (with greater insight and compassion) had in fact more knowledge of birds and beasts than Radagast, and was regarded by them with more respect and affection'

I was wondering about this because afterall 'birds and beasts' are supposed to be Radagast's specialty here. Yet, Gandalf knew more about them and got more respect from them then did Radagast. Why's that? As you point out all it really was, is Radagast was 'fond' of the birds and beasts and Gandalf tells Radagast to warn his 'friends.' But, I think when we see the interaction between Gandalf and Gwaihir we see the great respect Gwaihir has for Gandalf.

First off, Gwaihir rescues Gandalf from Orthanc. All Gwaihir was sent for was to act as a messenger, he wasn't expecting to have a passenger, yet because of his respect for Gandalf he gets him off Orthanc:

"How far can you bear me?" I said to Gwaihir.
"Many leages," said he, "but not to the ends of the earth. I was sent to bear tidings not burdens."~The Council of Elrond

Then later when Gwaihir fetches Gandalf off Zirak-Zigil:

"Ever am I fated to be your burden, friend at need," I said.
"A burden you have been," he answered, "but not so now. Light as a swan's feather in my claw you are. The Sun shines through you. Indeed I do not think you need me any more: were I to let you fall, you would float upon the wind."~The White Rider

And finally to rescue Frodo:

'Twice you have borne me, Gwaihir my friend,' said Gandalf. 'Thrice shall pay for all, if you are willing. You will not find me a burden much greater than when you bore me from Zirakzigil, where my old life burned away.'
'I would bear you,' answered Gwaihir, 'whither you will, even were you made of stone.'~Field of Cormallen

Eventhough we never see Radagast interacting with the animals he is 'fond' of. I think we do see what he meant that Gandalf did know more about the 'birds and beasts' than Radagast's did, and he had more respect from them. As we see a long list of one rescuing the other (though Gwaihir's list of rescuing Gandalf is much longer! ).

And we can kind of see that whitty friendly banter going on, with Gwaihir calling Gandalf a 'burden.' However, it all ends with Gwaihir saying 'I would will bear you wherever even were you made of stone.' What a happy ending.