Since birds' resources in nature are limited during the winter, they will flock to the backyards of humans in hopes of survival. There are a number of simple things that will take little time that anyone living in an area with a great number of species of wild birds can do in the winter to ensure these birds' survival. For one, you can put out food in your back or front yard for the birds. You can do this by placing the food in suitable feeder that the birds can reach easily. You don't even have to buy any new special food; things leftover from the morning's breakfast will do.
Since insects are scarce, birds will need adequate sources of protein. Providing peanuts, bacon, suet and mealworms will provide the protein and fat birds need in the winter. Whole grain foods such as rice, pasta, and oats, which are all most likely found around the house, are good foods for birds also. You can also leave out fruit, cooked potatoes, and forms of birdseeds. In the winter, birds will form flocks to increase their chances of survival. These flocks will gather around feeders to indulge in the food offered in them. The birds will appreciate the effort on your part.
Water is also scarce in the winter, as lakes and ponds are frozen over. Leaving a simple birdbath filled with water will give the birds a place to re-hydrate. Birds sometimes have to travel great lengths to find suitable sources of water. Providing the water will save the sometimes already starving birds the trouble. You can prevent the birdbath from freezing over by place floatable items like ping pong balls in the water. Another option is to place a heater in the birdbath to keep the water continuously warm.
Aside from water and food, it is a good gesture to provide the birds with shelter from cold. Placing a birdhouse or nest boxes will give birds a place to shield themselves from the cold. The shelter can also protect the birds from predators. Throughout the winter, try to keep a continuous supply of food and water from the birds. Keep any shelter provided for the birds clean on a regular basis. The birds may return to these roosting boxes to nest. It will be beneficial not only the birds but to the ecosystem as a whole to keep these birds alive in the winter.