Common ostrich
Breathing adaptations

The common ostrich has no sweat glands, and under heat stress they rely on panting to reduce their body temperature. Panting increases evaporative heat (and water) loss from its respiratory surfaces, therefore forcing air and heat removal without the loss of metabolic salts. Panting allows the common ostrich to have a very effective respiratory evaporative water loss (REWL). Heat dissipated by respiratory evaporation increases linearly with ambient temperature, matching the rate of heat production. As a result of panting the common ostrich should eventually experience alkalosis. However, The CO concentration in the blood does not change when hot ambient temperatures are experienced. This effect is caused by a lung surface shunt. The lung is not completely shunted, allowing enough oxygen to fulfill the bird's metabolic needs. The common ostrich utilizes gular fluttering, rapid rhythmic contraction and relaxation of throat muscles, in a similar way to panting. Both these behaviors allow the ostrich to actively increase the rate of evaporative cooling.

In hot temperatures water is lost via respiration. Moreover, varying surface temperatures within the respiratory tract contribute differently to overall heat and water loss through panting. The surface temperature of the gular area is 38 °C (100 °F), that of the tracheal area is between 34 and 36 °C (93 and 97 °F), and that of both anterior and posterior air sacs is 38 °C (100 °F). The long trachea, being cooler than body temperature, is a site of water evaporation.

As ambient air becomes hotter, additional evaporation can take place lower in the trachea making its way to the posterior sacs, shunting the lung surface. The trachea acts as a buffer for evaporation because of the length and the controlled vascularization. The Gular is also heavily vascularized; its purpose is for cooling blood, but also evaporation, as previously stated. Air flowing through the trachea can be either laminar or turbulent depending on the state of the bird. When the common ostrich is breathing normally, under no heat stress, air flow is laminar. When the common ostrich is experiencing heat stress from the environment the air flow is considered turbulent. This suggests that laminar air flow causes little to no heat transfer, while under heat stress turbulent airflow can cause maximum heat transfer within the trachea.
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