Barn swallows contribute to the ecosystem by eating an enormous amount of insects and controlling their populations.
Barn swallows eat an enormous amount of insects and are very important in the control of their populations. They are quite effective in reducing insect pest populations.
Barn swallows are also a useful food source for many predators.
Barn swallows can also serve as an indicator or trigger organism, indicating possible environmental trouble, as declines in their relatively abundant numbers may precede other more obvious effects of environmental stress.