Organismal Properties of Heat Transfer and Absorption

Regional heterothermy is maintained by countercurrent heat exchangers in the limbs of House Sparrows (Passer domesticus).

Do House Sparrows exhibit regional heterothermy through the use of countercurrent or non-countercurrent  heat exchange mechanisms? 
Introduction 

Thermal Microhabitats of animals.

Dynamics of energy exchange between animals and environment.

 Passerine birds experience regional heterothermy--heat conservation through the maintenance of higher core and lower peripheral body temperatures.  If core body temperatures were continuously cooled, animals could not maintain energy levels and thus could not grow and survive.  For this study we are focusing on cold stresses to House Sparrows and their responses to exposure to cold climate. (Modified from E.Zerba,Princeton University)

Heat exchange models.

Countercurrent heat exchange and non countercurrent heat exchange model.  Thermocouples are attached at six points along the insulated apparatus.  Coiled tubes represent capillaries in blood flow systems. (Apparatus designed by Franklin and Plakke 1988)

Heat exchange capillaries.

Close-up photograph of capillaries in heat exchange simulator.  The coils are placed in an ice-bath to simulate extreme temperature conditions on living organisms, specifically passerine birds that forage in the snow. (E. Zerba, Princeton University)

Heat exchange apparatus.

Main body of heat exchange apparatus.  The two copper tubes on the right are separated by insulation;  the two copper tubes on the left are connected in one insulation unit.  The unit on the right represents non-countercurrent heat exchange;  the unit on the left represents countercurrent heat exchange.

Control of fluid flow in heat exchange apparatus. Warm water from the faucet simulates blood flow from the heart. The flow is constant through the apparatus at a rate of 40 ml/minute. Ambient temperature is also constant at  22ºC.
Results

Changes in water temperature in a countercurrent heat exchange.  "In" represents arteries; "out" represents veins in passerine birds. Temperature readings from thermocouples show a standard error range from 0.09 to 0.05. Data from this model show that heat tends to be conserved by convection.

 


Changes in water temperature in a non countercurrent heat exchange simulator.  "In" represents arteries; "out" represents veins. Temperature readings from thermocouples show a standard error range from 0.13 to 0.18. The nonCCHE model has a greater heat loss when compared to the CCHE model.  

 

 

After ten minutes of exposure to cold conditions, similar to those in nature, the foot pad temperature of a House Sparrow is significantly lower then the core body temperature.  The core body temperature only slightly decreased from the optimum core body temperature of 45.2C.  Error bars indicate 1.07 standard errors above and below the mean for foot pad of three birds sampled; error bars indicate 1.30 standard error above and below the mean for core body temperature.  Note the standard error bars do not overlap, indicating a statistical significance to the data set.

 

Conclusion and Inferences

1)  Data obtained from foot pad and core temperatures of live birds   (House Sparrow) under simulated natural environmental conditions support our hypothesis that Passer domesticus birds exhibit regional heterothermy.

2)  Data from temperature readings taken with thermocouples of models of countercurrent heat exchange (CCHE) and non-countercurrent heat exchange (nonCCHE) show that CCHE system conserves more heat than the nonCCHE. We speculate that based on the data obtained in this model, P. domesticus may use a countercurrent mechanism. However, further investigations are needed to provide more conclusive evidence.

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