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How giraffes keep it cool

The African landscape would be incomplete without the majestic silhouette of the giraffe to adorn the savannah sunset tableau. Researchers at the Centre for Veterinary Wildlife Studies at the University of Pretoria (UP), have found benefits to this iconic animal’s unique shape that go beyond aesthetics to ensuring their survival on the arid African plains.

In a paper published in the Journal of Arid Environments, a collaborative study (led by Graham Mitchell from UP and the Department of Zoology and Physiology at the University of Wyoming) showed why the giraffe really has a long neck. UP’s Sybrand van Sittert and David Roberts also contributed to the study.

It is commonly held that giraffes evolved long necks to give them an advantage when feeding on the prized leaves of otherwise unreachable parts of acacia trees. This idea is supported by years of studies, which also argued that large, adult males are the ones most advantaged by this characteristic.

However, another theory proposes that the shape of giraffes’ bodies helps to control their body temperature by making them better at regulating their body temperature than their similar-sized counterparts. According to this theory, this benefit extends to all members of the species, rather than just to the tallest males.

The idea behind the body temperature control can be traced back to Allen’s Rule, which explains how men (and other mammals) who live in desert or tropical areas have a high surface area to body mass ratio. This means that they are usually tall and thin to better deal with the hot climate. In the case of giraffes, researchers hypothesised that their elongated legs and neck, in combination with their slender form, increases the surface area to mass ratio.

Giraffes have an average body temperature of 38.5° C and employ many ways to regulate their body heat. Mitchell and colleagues wanted to find out how their unique body shape helps them do this. They set out to measure the surface area and mass in the species Giraffa camelopardis giraffa, found in Zimbabwe.

Their calculations indicated that the total body surface area of a giraffe’s body is similar to the surface area of the bodies of other similar-sized mammals. The next step was to try and explain this finding. The team noted that the length of a giraffe's body measured from the base of the neck to the base of the tail, is shorter than that of a standard ‘cylindrical’ mammal of similar mass.

They compared their findings to data from a study conducted in cattle in 1923 and found that even though the surface area of the giraffe is not different from that of cattle, it does differ in terms of how it is distributed. The trunk and upper legs of the giraffe take up only 51% of the body surface area while their long necks and lower legs are a whopping 40% - these proportions are unusual when compared to a more conventionally-shaped mammal like an ox.

While a giraffe’s overall surface area to body weight ratio remains similar to other large mammals, the researchers say that it is the thinness of their legs and neck that leads to better regulation of body temperature. Because of the narrowness of its legs and neck, the giraffe will experience an increased cooling effect from air movement when it moves around, while the long legs lift it above the intense heat and low wind speed close to the ground in arid landscapes. Together, this makes temperature control for giraffes a breeze in extremely hot climates.


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