#4 Clogged gutters
Another place where birds can turn their attention in order to build their nest (if they bypass the chimney) is the gutter. This can happen because they prefer high places where they can be safer from predators. If you have an eavestrough, that one is a bird magnet as they can easily access the fresh water that is gathered there, and water is also a breeding ground for insects, so they will flock towards it.
If they make a nest in your gutter, you are putting your home at risk of potential damage. Not only will it block your gutter and lead to potential floddings, but the extra constant weight on it can make the whole system sag or loosen, as well as cause siding and wall damage. You can end up with the whole thing falling off the house, and replacing a whole gutter system is going to cost you a pretty penny.
