Marvin H. Bernstein

Brain temperature in pigeons: Effects of anterior respiratory bypass

SummaryDuring heat stress in domestic pigeons (Columba livia, mean mass 0.43 kg) brain temperature (TB) varied in parallel with colonic temperature (Tc). The difference between these (TC−TB=ΔT) averaged 0.7°C and was not significantly altered when the animal breathed through a trachael cannula bypassing the buccopharyngeal cavity. When we sealed the nares and beak in bypass animals, ΔT was significantly reduced but was nevertheless maintained at 0.4°C. When the eyes were sealed as well, however, ΔT was reversed, amounting to −0.4°C. Conversely, with eyes sealed but beak and nares open, ΔT was indistinguishable from that in controls. These results suggest a role for the cornea in evaporative cooling, at least when respiratory evaporation is impaired, and are consistent with the hypothesis that buccopharyngeal and corneal evaporation are coupled to brain cooling. The probable mechanism for this coupling is the flow of venous blood from evaporative surfaces through theretia mirabilia in the temporal areas. Here heat is transferred from the warmer arterial blood flowing through theretia toward the brain to the centrally flowing, cooler venous blood.

Brain temperatures in birds

Summary1.Brain (hypothalamic) and cloacal temperatures were measured in heat-stressed Lesser Nighthawks (Chordeiles acutipennis), Mallards (Anas platyrhynchos), Pigeons (Columba livia), and White-Necked Ravens (Corvus cryptoleucus) and in one Roadrunner (Geococcyx californianus). Range of mean body masses was 0.047 to 1.156 kg.2.In all these species brain temperatures were always below cloacal temperatures (Fig. 1). The body-to-brain temperature difference was maintained nearly constant within a species over a wide range of cloacal and air temperatures, and varied in magnitude from 0.80°C in the Roadrunner to 1.29°C in Mallards.3.The presence of arete mirabile ophthalmicum was demonstrated in all five species. This rete may be associated with the observed pattern of brain temperature control.4.The body-to-brain temperature difference may be important in avoiding brain damage during core hyperthermia.

Birds Conserve Plasma Volume during Thermal and Flight-Incurred Dehydration

Dehydration tolerance in mammals is associated with the degree to which an animal is able to maintain plasma volume. During thermal dehydration, rock pigeons (Columba livia), quail (Coturnix coturnix japonica), and white-necked ravens (Corvus cryptoleucus) maintained nearly constant volumes despite mean body mass losses of 17%, 15%, and 13%, respectively. During flight-incurred dehydration in tippler pigeons (C. livia), no changes occurred in plasma volume although the birds lost 6%-10% of their preflight body mass. Thus, dehydrated birds were found to be excellent plasma volume conservers, like the most xericadapted mammal species. We suggest that plasma volume conservation in birds is an adaptation associated with high heat loads incurred during flight. In contrast, plasma conservation in mammals is associated with their ability to inhabit arid environments.

Ventilation and Acid-Base Status during Thermal Panting in Pigeons (Columba livia)

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Development of Brain Temperature Regulation in the Hatchling Mallard Duck Anas platyrhynchos

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Respiration by Birds at High Altitude and in Flight

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Body and Brain Temperatures in Pigeons at Simulated High Altitudes

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