Strategies of thermal protection in arctic animals.

Anatomical, physiological and behavioural adaptations to cold and lack of food combined with long periods of darkness are discussed. In large animals such adaptations comprise body size and insulation and controlled peripheral cooling in the legs and heat exchange in the nasal passages, whereby expiratory heat and water loss is minimized. In such animals grave thermal problems are incurred when the animal is forced to run. In some species the heat exchanger in the nose is operated in conjunction with a carotid rete for selective cooling of the brain. Small and poorly insulated mammals evade the brunt of the cold arctic winter in nests under the snow were convective heat loss is eliminated and ground heat creates a relatively comfortable micro-climate. Most newborn mammals are poorly insulated, but some survive birth, wet and miserable, at ambient temperatures down to -30 degrees C. Precocious forms depend heavily on NST in brown fat and skeletal muscle. Altricial forms are born very small and naked and are virtually ecto-thermic at birth. They depend on shelter and/or huddling, but survive a cooling of body core down to +2 degrees C.