Heat conservation during cold exposure in birds (vasomotor and respiratory implications)

Abstract

1983: Heat conservation during cold exposure in birds (vasomotor and respiratory implications). Polar Research I n.s., 259-268.The mechanisms by :vhich peripheral circulation and respiration serve in maintaining thermal homeostasis in birds living in cold climates are reviewed. Three types of arteriovenous heat exchanger (an elaborate rete, asimple rete, and a venue comirantes system) are found in the legs of birds. The anatomical differences between the different types of A-V associations are described, and the regulation of peripheral blood flow, in respect to maximal heat conservation and prevention of tissue damage, is discussed. A nasal temporal counter current heat exchanger, lowering the temperature of the expired air to values considerably below the body temperature, is the most important mechanism for minimizing the respiratory heat and water loss. In addition, a decreased ventilatory requirement, caused by a changed respiratory pattern and an increased parabronchial oxygen extraction, lowers the amount of air ventilated relative to the amount of oxygen uptake. Thus, the relative loss of heat and water is reduced.

The evolution of the avian bill as a thermoregulatory organ

“…These anastomoses are much larger in diameter than capillaries, which allows for much larger amounts of blood flow to reach the periphery, thereby facilitating convective heat transfer from the core of the body to the periphery. In some species, the legs are very important for heat dissipation in warm climates and during flight (Johansen & Millard, ; Baudinette et al ., ; Johansen & Bech, ; Martineau & Larochelle, ; Maloney & Dawson, ). For an emu ( Dromaius novaehollandae ), heat loss through the legs can account for almost 40% of total body heat loss at rest (Maloney & Dawson, ).…”

Thermoregulation in ratites: a review

“…Thus, in cold conditions, blood flow to the shell is reduced and peripheral tissues cool. With limited blood flow, heat flow through those tissues becomes a function of the thermal conductance of those tissues, and the shell thus contributes to reducing heat loss from the core to the environment (Johansen and Bech 1983). In contrast, in hot conditions the shell is perfused with arterial blood, facilitating the delivery of heat to the body surface, thus negating the contribution of peripheral tissues to insulation and increasing heat loss from the body core.…”

“…These changes in VT and EO 2 accounted for 47 and 31%, respectively, of the change in V ⋅ O 2 between 25 and -5°C. Increasing EO 2 at low ⋅ environmental heat gain by ~1 W. But the largest contributor to temperatures has often been interpreted as a mechanism to the reduced evaporative requirement for thermal balance was the reduce respiratory heat loss (Johansen and Bech 1983). But this adaptive interpretation has been questioned by Chappell and V reduction in C dry from 3.5 W/°C to 2 W/°C, which resulted in a 15 W decrease in environmental heat gain (Maloney and Dawson Souza (1988) because at low temperatures O 2 usually ⋅ ⋅ 1998).…”

“…This feature probably evolved in response to the requirement for conditioning the volumes of air associated with higher resting and activity metabolic rates (tachymetabolism) in these homeothermic classes. But acting in concert with the autonomic control of blood flow to the turbinates, the morphology also serves to recuperate heat and water from expired air (Johansen and Bech 1983). When air cooler than T b is inspired, heat is transferred from the nasal mucosa to the air, warming the air, increasing its saturation vapour pressure and enhancing evaporation from the mucosa to the air.…”

Metabolic and Ventilatory Acclimatization to Cold Stress in House Sparrows (Passer domesticus)

“…However, the only passerine bird studied under severe (helox) cold stress, the black-capped chickadee, increased Eo 2 to support metabolism (Cooper and Same 2000). Johansen and Bech (1983) have suggested that an increase in Eo 2 in response to cold may be an adaptation to reduce respiratory heat loss by reducing . However, the num-V I ber of passerine birds studied so far is insufficient to establish any possible patterns of ventilatory accommodation to increased oxygen demands.…”