They usually return the following year and the whole process must be repeated. Exclusion Exclusion refers to any control method that denies physical access to the nest site area. Exclusion represents a relatively permanent, long-term solution to the problem. In California, a permit is not required for this method if it is done before the birds arrive, during nest building when there are no eggs or young in the nest, or after the birds have left for the winter. If swallows have eggs or young in the nest, exclusion may not be used without a permit.
Netting can provide a physical barrier between the birds and the nest site.
If a plastic net is used, it should be attached so that it can be pulled taut. This prevents flapping in the wind, which looks unsightly and results in tangles or breakage at mounting points. The net should not have any loose pockets or wrinkles that could trap and entangle birds. Netting can be attached using tape, staples, or hooks on the eaves and the side of the building. An advantage of hooks is that the net can be taken down during the nonbreeding period or for maintenance of light fixtures, painting, etc.