MANY BIRDS DEPART FOR WARMER CLIMATES when winter comes. But the presence of chickadees, finches, and other small birds at winter feeders attests to the fact that quite a few species stick around all winter long. On warmer winter days these birds' layers of feathers and down keep them quite warm, especially when friendly humans help to make sure they are able to meet their calorie needs. But where do they go at night and in harsh weather?
The importance of evergreens
In harsh weather birds seek shelter just as we do. Dense evergreens are often used for this purpose, which is one of many reasons why it's good to include evergreens in your wildlife-friendly garden. Evergreens that are left to grow naturally--not pruned or limbed up--typically provide better shelter. An evergreen that has been very heavily pruned (for example, to form a hedge) may be so dense that birds can't get into it, making it useless as shelter.
The importance of dead trees
Quite a few species of birds hide from storms in holes in dead or dying trees. Chickadees prefer to nest alone in a cavity just large enough to shelter a single bird. But some species, such as finches, will roost in the same cavity in order to share body heat.
Sadly, dead and dying trees are increasingly difficult to find. You may be able to provide an alternative, however, by putting up what's known as a roost box. This is similar to a nest box in that both are attempts to duplicate a cavity in a dead or dying tree. A roost box is designed for winter use, however, whereas a nest box is designed for use in warmer weather.
How a roost box is different from a nest box
As shown in the diagram above, a roost box is designed to hold in heat: There are no ventilation holes in the top of the box, and the entry is down toward the bottom. Typically the box has perches on the inside, allowing one or more birds to sit comfortably.
In contrast, the nest box does have ventilation holes under the roof. There are no perches in the box because the bird doesn't use it for perching: She builds a nest for her eggs down in the bottom of the box. Placing the entry at the top of the box helps to protect the eggs and baby birds from predators. Often the inside front of the box is roughened or ridged to help the young birds climb out of the box when it's time to leave.
How roost boxes are similar to nest boxes
Neither a roost box nor a nest box should have a perch on the outside. The birds don't need one, and putting a perch on the outside of the box just gives predators something to stand on. Both should have drainage holes in the bottom. Both should have a door that can be opened for cleaning. The exact dimensions of the box will vary depending on the species you're trying to attract; the entry hole should be as small as possible in order to deter predators.
I've found that birds generally won't use nest boxes or roost boxes if there are natural cavities available in the area. (This is a very good reason to protect those dead and dying trees!) However, these are good additions to your property if you live in an area where all the old, dying trees have been cut down.
How to make your own
If you're handy with wood, making roost boxes and nest boxes is an enjoyable project; the boxes are decorative, and there is always at least some chance the birds will use them. Plans for roost boxes are readily available online. Here are a few sites: