Quote from "Respiratory and Heart Rates of Birds at Rest," William Calder, "The Condor," October 1968 (unavailable without $).
"Respiratory rates are increased to compensate for metabolic acidosis during formation of CaCO
3 for egg shells (Mongin and Lacassagne, 1965)..."
From Wikipedia: "Metabolic acidosis is a condition that occurs when the body produces excessive quantities of acid or when the kidneys are not removing enough acid from the body. If unchecked, metabolic acidosis leads to acidemia, i.e., blood pH is low (less than 7.35) due to increased production of hydrogen ions by the body or the inability of the body to form bicarbonate (HCO3
-) in the kidney. Respiratory compensation (hyperventilation) will cause more carbon dioxide to be removed from the body and thereby increase pH."
I was hoping to find research on a subject that came up in chat, namely, why is Mom panting in relatively cool temperatures? I assumed it was because of excess heat generated by incubation. The amateur sleuthing I did, above, suggests an additional explanation. Mom may still be recovering from laying 3 eggs.