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CAN OSTRICHES KEEP A COOL HEAD?
kathryn{at}biologists.com
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For any animal that's stood out in the savannah, it's important to keep your cool with the sun beating down on your head. However under some conditions, mammals that are exposed to extreme temperatures seem to be able to cool their brains as the temperature rises; but not always. Could ostriches that roam across South African grasslands protect themselves from the heat by keeping their brains cool? Andrea Fuller and her colleagues at the University of Witwatersrand decided to monitor the brain and body temperatures of free ranging ostriches, to see if the birds selectively cooled their brains (p. 1171).
After tracking the birds' temperatures for several months, the team were surprised to discover that the ostriches' brains were slightly warmer than their body temperature, and only occasionally cooled below body temperature during the afternoon. More surprisingly, their brain temperature was higher than their blood temperature by 3°C at night! Fuller believes that instead of using cooling to protect their brains from overheating, mammals cool the hypothalamus to reduce evaporative heat loss and protect themselves from dehydration during the heat of the day; but it seems unlikely that birds use brain cooling in the same way. In fact, she adds that ostriches seem to use selective brain cooling so rarely that it might `serve no current physiological function' for these big birds.
References
Fuller, A., Kamerman, P. R., Maloney, S. K., Mitchell, G. and
Mitchell, D. (2003). Variability in brain and arterial blood
temperatures in free-ranging ostriches in their natural habitat. J.
Exp. Biol. 206,1171
-1181.
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