1/8/2023 0 Comments Arabian orx![]() ![]() Many species of endotherms control their core body temperature( T b) within narrow limits (☒☌) even when subjected to a wide range of environmental temperatures, a process called homeothermy ( International Union of Physiological Sciences Thermal Commission, 1987). If heat storage was calculated based on the daily change in T b rather than on heat storage above mean T b then we estimated that oryx saved 0.538 litres H 2O day –1 animal –1during summer. Without heat storage in summer, we estimated that oryx would have to increase their water intake by 19%, a requirement that would be difficult to meet in their desert environment. Todissipaterequirethisheatin summerby evaporation0.28 litres H 2O day –1 animal –1and0.11 litres H 2O day –1 animal –1 in summer and winter,respectively. The use of heterothermy by oryx resulted in storage ofandwould672.4 kJ day –1 animal –1258.6 kJ day –1 animal –1in winter, if heat storage is based on calculations involving mean T b. Behavioural thermoregulation was used by oryx to cope with thermal stress during summer: animals lay down in shade in the morning shortly before T a exceeded T b and remained there until evening when T b– T abecame positive. Throughout the year, daily variation in T b appeared to reflect thermal load( T a,max– T a,min) rather than an endogenous rhythm. The minimum T b was lower in summer (36.5☑.16☌) than in winter (37.5☐.51☌)despite the fact that the temperature gradient between T band air temperature ( T a) was larger and solar radiation was lower in winter. During the day in both summer and winter, T b increased continually, suggesting that oryx store heat instead of dissipating it by evaporation, whereas at night T b decreased. Over both seasons, mean T b was 38.4☑.3☌. We report the first case of heterothermy in a free-living ruminant in a desert environment: T b varied by 4.1☑.7☌ day –1 during summer (June to September) and by 1.5☐.6☌ day –1 during winter (November to March). To test the idea that large, free-living, desert ungulates use heterothermy to reduce water loss, we measured core body temperature( T b) of six free-ranging, adult Arabian oryx ( Oryx leucoryx) during 2 years in the arid desert of west-central Saudi Arabia.
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