Waste is Normal?? Lessons from a Bird Feeder

My husband has become a birder. He hung up a bird feeder on our back porch and every few minutes or so I catch him looking outside to see who is munching away on his treats. He checked out a bird field guide from the library and keeps telling me the names of the various finches, sparrows, and our beloved cardinals that pay us a visit. His love for the birds is a treat for me to see because as a lifelong asthmatic with allergies to "everything alive", he doesn't get many opportunities to interact closely with nature. But his bird friends are perfect - he can enjoy them, learn about them, and they don't stay in his house and make him sneeze!

I can't remember the names of the bird species that pay us a visit (my memory is notoriously terrible), but remembering the names of the species isn't as appealing to me as trying to figure out how they work and what lessons we can learn from them. So what is my main takeaway from observing our bird friends so far? 

Waste is normal. 

This observation is a bit shocking to me. It flies in the face of all sustainability theory I've read and practiced for the last fifteen years, so so how can I observe that waste is normal? Because it is, when you look at component parts in isolation without seeing the larger system. Not every species can consume the entirety of the resources that are offered. Sometimes, there is waste, but this waste is readily taken up by another component, resulting in a zero-waste system.