Birds love to build their nests in ferns. Here are a few ways to deter them without harming them: 1. Pluck the nest out as the birds are trying to build in the fern. 2. Add reflective material to the fern like a metallic pinwheel or mirror tape. 3. Place a rubber snake inside the fern. 4. Place wooden sticks in the fern to prevent a good nesting place (not pointy sticks though as we don't want to hurt the birds). 5. Place dog hair and cayenne pepper in the fern.