I have a commercial feeder where the cover is retained by the hanger, I took that concept and combined it with the design concept by welwell(https://www.thingiverse.com/thing:181885), where the feeder uses 1/4" (6mm) wire mesh (AKA hardware cloth) to retain the seeds.
This should be printed from an outdoor stable sunlight tolerant plastic, painting the plastic would also extend its life as it would shade the sunlight.
Mesh_Feeder_Base.stl | 707.0KB | |
Mesh_Feeder_Cap.stl | 3.6MB |