in Thoreau’s Journal:

I am not aware of growth of any plant yet, unless it be the peeping out of the willow catkins. They have crept out further from under the scales, and looking closely 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.