I guess we think singing requires a good mood. Despite this, I cannot really be sure that a bird feels happy when he or she is singing.
This little fellow was chirping quite a complex little tune at the edge of the Fraser River. I stopped as I was walking past, but he continued with renewed gusto. He may or may not have been happy; he undoubtedly helped me feel that way though.
I listened for a couple of minutes and made sure to thank him for the free entertainment before I continued along.