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Thermoregulation in a large bird, the emu (Dromaius novaehollandiae)

Abstract

The emu is a large, flightless bird native to Australia. Its habitats range from the high snow country to the arid interior of the continent. Our experiments show that the emu maintains a constant body temperature within the ambient temperature range-5 to 45°C. The males regulate their body temperature about 0.5°C lower than the females. With falling ambient temperature the emu regulates its body temperature initially by reducing conductance and then by increasing heat production. At-5°C the cost of maintaining thermal balance is 2.6 times basal metabolic rate. By sitting down and reducing heat loss from the legs the cost of homeothermy at-5°C is reduced to 1.5 times basal metabolic rate. At high ambient temperatures the emu utilises cutaneous evaporative water loss in addition to panting. At 45°C evaporation is equal to 160% of heat production. Panting accounts for 70% of total evaporation at 45°C. The cost of utilising cutaneous evaporation for the other 30% appears to be an increase in dry conductance.

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Abbreviations

A r :

Effective radiating surface area

BMR:

basal metabolic rate

C dry :

dry conductance

CEWL:

cutaneous evaporative water loss

EHL:

evaporative heat loss

EWL:

evaporative water loss

FECO2 :

fractional concentration of CO2 in excurrent air

FFH2O :

water content of chamber excurrent air

FEO2 :

fractional concentration of O2 in chamber excurrent air

FICO2 :

fractional concentration of CO2 in incurrent air

FIO2 :

fractional concentration of O2 in chamber incurrent air

MHP:

metabolic heat production

MR:

metabolic rate

REWL:

respiratory evaporative water loss

RH:

relative humidity

RQ:

respiratory quotient\((\dot VCO_2 /\dot VO_2 )\);

SA:

surface area

SEM:

standard error of the mean

SNK:

Student-Newman-Keuls multiple range test

STPD:

standard temperature and pressure dry

T a :

ambient temperature(s)

T b :

body temperature(s)

T e :

surface temperature(s)

\(\dot V\) :

flow rate of air into the chamber

\(\dot VCO_2\) :

carbon dioxide production

\(\dot VO_2\) :

oxygen consumption

\(VP_{H_2 O}\) :

vapour pressure of water

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Maloney, S.K., Dawson, T.J. Thermoregulation in a large bird, the emu (Dromaius novaehollandiae). J Comp Physiol B 164, 464–472 (1994). https://doi.org/10.1007/BF00714584

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Key words

  • Cutaneous evaporation
  • Panting
  • Ratite
  • Thermoregulation
  • Emu,Dromaius novaehollandiae