For people, it should be "贴秋膘"， for ur painting ,better be “”临冬“。”

Saying something about preparing for the winter explicitly may not be too interesting. If the painting is more about the birds, I would say something like: - Birds Before Another Winter (use species name if you can, like "Sparrows", etc) - Where to Winter This Year? (for a cute, facetious effect) If the painting is about the tree, maybe A Tree on The Verge of Winter, or A Tree Before Winter.

Try posting as a Chinese learning and English base language.