If you want to help birds who are having their natural environments disappear due to human encroachment, try helping to build bird houses for them to nest in. But what exactly makes for a good birdhouse?
The question is unanswerable in a sense. After all, a good bird house is different for each species of bird. What makes a good wren bird house is not necessarily what makes a good birdhouse for a robin and vice versa. A good birdhouse is built for the type of bird that you desire to inhabit it. But there is one primary trait that even the simplest bird house should have – even one as uncomplicated as a pop bottle bird house.
One of the most important traits that a good birdhouse must have is ventilation – top and bottom. There should be holes at or near the top of the bird house to let hot air escape during hot weather. Lack of ventilation can cause heat stress in birds as the interior temperature of the bird house rises. The lack of ventilation is especially acute when the roof of the bird house is poorly insulated, a major cause of overheating. Birds have no sweat glands and can only get rid of excess heat by panting. In hot and humid atmosphere, however, it can be difficult for them to pant enough to lower their body temperature. Ventilation helps to keep the interior temperature stable by creating cross breezes in the bird house.
Just as important as top ventilation is floor ventilation. By necessity, every bird house has one or more holes in it. Thus in a heavy rainstorm, even a well built one can take on water. Holes or ventilation in the bottom of the bird house prevents water from building up and allows excess water to drain. These holes prevent water from collecting at the base of the bird house which can lead to dampness and mold and fungus build-up. Good drainage will also prevent baby birds from drowning during a heavy rain.

