Time: Depends on how elaborate you want to be
Skills Needed: Tying, spreading, etc.
WHAT! You think the Nature Army can afford to take the winter off!!! We have work to do!
Actually, winter is a convenient winter timing for lots of Nature Army tasks, both indoors and (shiver) outdoors. Though I'm posting this after the holidays, we did this on the 24th of December. (We are experiencing technical difficulties. Please stand by.) And yes, contrary to popular belief, it is OK to put up winter decorations after the holidays.
A while ago, my siblings and I decorated an outdoor holiday tree (fine, a holiday branch) for the birds. The ornaments are English muffins spread with peanut butter and covered in birdseed. We tied them on our branch (which, by the way, gives a stunning view of the stream nearby) with fleece strips leftover from making blankets for the animal shelter. (You can find out more about that at http://www.naturearmy.com/2011/08/blanket_for_cats.html)
To make this delightful snowman, we used a cookie cutter to cut the shape out of the end of a loaf of bread. Looking back, it would have been more fun to forget the English muffins and just use cookie cutters. Obviously, we arranged the birdseed to make a nose, eyes, buttons, and the hat.
If you don't have birdseed, there are many other things you can use. Dried fruit, bread crumbs, peanuts, and cereal in moderation will often attract birds like sparrows and cardinals. We didn't use this idea, but you could also string cranberries and popcorn on your tree like tinsel.
String your ornaments with yarn, strips of fabric, or twine loosely, so the birds can take the strings for their nests, and you may also want to put out a birdbath. It can just be a soup plate filled with water (not too deep, or they won't be able to stand in it).
To get into the Nature Army with this, you can make your own tree/branch. Please don't put up a bird feeder and tell us about it. Take the time to put together something really special. You can make your own tree, or build a bird feeder yourself. Maybe you could get some friends together to make a bird bath. By the way, the birds really do like this; less than a week after we put it up, it was gone.
Right now our ornaments are limited to peanut butter, bread, and birdseed/cereal, so if you have any ideas, post a comment and tell us about it! You can find more ideas on helping backyard birds and gardening at http://www.birdsandblooms.com/. So, uh, yeah. One-sided good-byes are awkward.