Our recent cold spell has given me cause to reflect on what wild birds need to survive in winter. Birds are warm-blooded and have a high metabolism, requiring enormous food intake to maintain a fairly constant body temperature in order to survive.

If there is ever an important time of year to feed wild birds, it is in the cold winter months when natural food sources are difficult to find. During the summer months, there is an abundance of food, the days are long and warm and they can forage up to 14 hours per day. In winter, they face just the opposite situation. They are stressed by cold conditions, food sources are limited, and shortened days give them less time to forage for food.

When you think about the needs of wild birds, it is not so different from what our basic needs are - food, water and shelter. Providing a birdhouse or "nesting box" in winter is just as important as providing one during breeding season. Birdhouses provide a place for birds to go at night to get out of the elements, and it is not uncommon for birds to roost communally, sharing body warmth as they huddle together.

Examples of both cavity nesting and cavity roosting species in the Central Highlands area of Arizona include mountain chickadee, Bewick's wren, bridled and juniper titmice, western bluebirds, nuthatches and woodpeckers, to name a few.

Earlier this week I received the following e-mail: "We have a bird bath that we had hooked up to the drip system. We have turned off the drip system for the winter, but I was filling the birdbath by hand. Now that we are having more freezing nights, should I let the bird bath go dry?"

This is a great question. When you think about our need for water, it is recommended that we drink approximately eight cups of water every day. Our need for water does not change seasonally - it changes based on our activity level. The same can be said for birds. It is just as important for wild birds to drink water in winter as it is in summer.

Maintaining an open source of water is a critical component when creating an inviting backyard wild bird habitat. There are two primary reasons birds need water. One, of course, is for drinking, and the other less obvious need is for bathing to clean their feathers. Clean feathers increase their insulating capacity. Dirty or matted feathers are not as effective at trapping warm air and insulating wild birds from the bitter cold nights and brisk daytime winds.

I find it fascinating that even in the dead of winter birds instinctively know that they need to bathe to keep their feathers clean. Watching birds bathe when it is in the 20s or 30s runs a chill up my spine, but they don't seem to mind the experience at all.

There are a couple of ways you can provide open water in winter. You can empty your birdbath each night and refill it each morning. If you don't empty your birdbath, use a pot of hot water each morning to melt the ice. The best choice is to use a birdbath that has a built-in thermostatically controlled de-icer, or put a thermostatically controlled bird- bath de-icer in your existing birdbath. No matter how you do it, the answer to the original question is a resounding NO! Do not let your birdbaths go dry in winter.