Nest Cleaning

We have hanging flower baskets on the porch and its necessary to water them every other day.  My "other chores" include feeding the fish, filling the bird feeders and watering the rest of our flowers. While enjoying a cup of coffee on the porch I  noticed a sparrow would land on the hanging basket and crawl in the foliage.  I took a closer look and found it had a nest which had 2 eggs.  I quiet watering and in a few days, the eggs hatched and eventually they fledged and flew off.  

The plants had died from lack of water and I took the basket down and examined the nest.  What I found was interesting and provided a "lesson."   Few would actually say they enjoyed "house keeping": however, if you were a bird you would find literally distasteful. 

Upon close examination, I found the inside of the nest remarkably clean.  However, there was a thick ring of bird droppings that surrounded the nest.  The only way those would have gotten there is by the parents cleaning and discarding their offspring's waste with their beaks.  I wonder if birds can spit?