in Thoreau’s Journal:

I am not aware of growth in any plant yet, unless it be the further peeping out of willow catkins. They have crept out further from under their scales, and, looking closely into them, I detect a little redness along the twigs even now. You are always surprised by the sight of the first spring bird or insect; they seem premature, and there is no such evidence of spring as themselves, so that they literally fetch the year about. It is thus when I hear the first robin or bluebird or, looking along the brooks, see the first water-bugs out circling. But you think. They have come, and Nature cannot recede.