Modern Birds: High Efficiency
Adaptation to high energy demand of flying
Respiration: re-design of lungs with air sacs near and within hollow bones -- two-phase breathing with unidirectional gas flow through parabronchi ? more efficient gas exchange
Circulation: 4 chambers heart, ventricle fully divided ? no mix of aerated and non-aerated blood; heardbeat in flying birds high (human ca. 70 min-1, ostrich ca. 70 min-1, hummingbird ca. 600 min-1)
Endothermy: hoemotherm, 40°C to 42°C body temperature ? metabolic processes faster