I recognize that there are a few discussions on here already about how humans can properly survive a multi-year winter on Planetos, but I've not yet seen one about the animals. Note that my question is totally notwithstanding the possible conversion of animals into wight-imals.
Specifically, thinking of the fact that even animals in our world end up often hibernating for a few months during the worst of the winter, and all the animals able to be active in the winter are specially adapted for doing so, I'm wondering how it is that common animals such as deer and birds which are not adapted for polar conditions can find enough food and warmth to get through multiple years of winter (especially the ones that last a decade or more).
Carnivores would probably have it good for a while, but I don't see herbivores lasting long without ample plant life, and carnivores won't last long without herbivores.
I've read the whole series several times, and am aware of no real discussion of how wild animals manage. Perhaps something in a world book or interview? I'd prefer a book answer, but if this was mentioned in the TV show then I suppose that would be interesting as well.