Birds Physiology (Lecture 7) PDF

Physiology (Lecture 7) High Body Temperature Birds have many physiological adaptations o - Metabolism o - Temperature regulation o - Feeding/digestion o - Water economy Endothermy – maintenance of body temperature thr...

Physiology (Lecture 7) High Body Temperature Birds have many physiological adaptations o - Metabolism o - Temperature regulation o - Feeding/digestion o - Water economy Endothermy – maintenance of body temperature through metabolic heat o - Birds maintain high body temperatures (~40° C or above) o - Rate of physiological process increases with temperature o - With 10° C increase in temperature: nerve impulses travel 1.8 times faster; muscle-fiber contractions triple in speed Birds have highest body temps of all endothermic vertebrates o - Energetically expensive – 20-30x more energy required than cold- blooded reptiles o - Greater endurance – can maintain powered flight for hours or days o - High activity levels and endurance open new ecological opportunities to birds Respiratory System Respiratory system of birds different in structure and function from other animals o - Birds lungs small and compact, molded along ribs o - Bird lungs weigh as much as equal body-weight mammals, but only 1⁄2 the volume  Air sacs – thin-walled, nonvascular, membranous compartments o - Extend throughout the body cavity, cervical vertebrae, and major wings bones o - Connected to lungs and bronchi through accessory channels called secondary bronchi o - Contraction of sternum and ribs compress air sacs (no diaphragm) o - In flight expansion/contraction of furcula help pump air o - Most birds have 9 air sacs (vary from 6-12) o - Also play a role in dissipating internal heat o - Therapod dinosaurs have pneumatized vertebrae consistent with the presence of anterior and posterior air sacs Inhale through nares (nostrils) at base of bill - Some birds have operculum (flap) that covers nostrils for protection (diving birds, hummingbirds) Conchae – elaborate folds in nasal cavity of birds o - Increases surface area of which air flows o - Cleanse and heat the air o - Examples from Northern Fulmar (top) and Turkey Vulture (bottom) Olfactory tubercles – contains olfactory receptors to sample air in conchae Rete mirabile – Network of nerves and blood vessels that help control rate of heat loss in body o Air moves down trachea and divides into two bronchi leading to the lungs o - 1,800 smaller interconnected tertiary bronchi o - Tertiary bronchi lead into tiny air capillaries that intertwine with blood vessels for gas exchange o Unidirectional airflow through air sacs and lungs o - Two complete cycles in inhalation/exhalation to move single volume of air through system o - Efficient gas exchange o Cycle: o - Inspiration 1: Trachea -> Posterior air sacs o - Expiration 1: Posterior air sacs -> Lungs o - Inspiration 2: Lungs -> Anterior air sacs o - Expiration 2: Anterior air sacs -> Trachea  o Alligators have small regions of unidirectional air flow (evolutionary precursor?) Circulatory System High metabolic rates require rapid blood circulation of high volumes of blood o - Deliver oxygen to body tissues; remove CO2 o - Delivers fuel (glucose) and remove toxic waste  Birds have double circulatory system and four-chamber heart (like mammals) o - Evolved convergently in birds and mammals o - Complete separation of pulmonary and systemic circulation Avian hearts typically ~40% larger than mammal of same size o - Hummingbird hearts 2-4% of body mass (most small mammals