This is one of my favourite poems, James Grant put some music to it on his album 'I Shot the Albatross' Well worth a listen. I think the underlying message is that we, by our nature, do tend to ruin the world we live in, be that with our technology, our attitude or even apathy, In the poem we are waiting to hear something from the radios, it takes the intervention of the horses to show us the way and bring us into action. Perhaps the message could be that no matter what we do, nature will come through for us in the end, maybe then we realise what we had in our forefathers time. It is an optimistic point of view, perhaps the message is to change our ways before this happens. I don't believe all is lost, I just think we have to consider what we are doing more carefully, Muir knew this even then, perhaps we have not learned as yet.