No, I am not talking about your retirement fund, however that is also important.  The UC Hopland Research & Extension Center maintains over 200 nest boxes for cavity-nesting passerine birds.  This group of birds includes such species as Oak Titmouse, White-breasted Nuthatch, Western Bluebird, Ash-throated Flycatcher, Tree Swallow, Violet-green Swallow, and House Wren.  

Each species has a certain "MO" ...or "Method of Operation" on how it goes about making its nest.  Experienced ornithologists can usually identify a nest by its location, shape, components, and "style".   The swallows always line their nests with feathers.  Here you see a Violet-green Swallow nest in an opened nest box.  

These 200-plus nest boxes are not currently being used for research, and are available for use and data gathering.   They are located at four different elevations on the Center.