From my speculation it is loss of habitat and global warming
Chitin - part of insects hard body and part of fungus
Cellulose - part of plant cell walls
Pectin - also part of plant cell walls
I need more of a sentance to anwser anything
Well considering birds follow humane rules, their selection and environment around them being thriving could effect their songs in a positive way. While a bird with a low selection of environmental stuff around them would effect their songs in a bad way giving off a more down manner.
Q1. It originates in the spinal cord, not the brain
Q2. The environment and sensory receptors
Q3.Breathing during sleep
Q4. Reacts to a threat; Calms you down
Q5. Somatic nervous system