The Open Door Web Site
Part XVIII: Energy and Activity : Activity in a Changing Climate Index
The polar bear is the biggest of all bears. An adult male may have a mass of over 800kg.
ENERGY AND ACTIVITY
Keeping Warm Requires Energy
A 'warm-blooded' animal, such as a fox, can maintain its body temperature at 37°C even when the air temperature falls below 0°C. The arctic fox can withstand temperatures of -50°C without any problem. 'Warm-blooded' animals stay warm by producing heat energy. To make this heat energy the animal needs food and oxygen so that it can respire. Therefore when the weather becomes colder 'warm-blooded' animals breathe in more oxygen and eat more energy-giving food.
The sun bear is the smallest species of bear
As a general rule animals with big bodies lose heat more slowly than animals with small bodies. The reverse is also true, animals with big bodies warm up more slowly than small animals. Therefore it is an advantage to have a big body if you live in a cold climate because you do not lose your body heat so quickly. It is an advantage to be a small animal in a hot climate because you will be able to cool off more quickly if your body becomes too hot.
This rule works quite well for most groups of animals. For example the biggest species of bear is the polar bear (the males can weigh up to 600 kg) and the smallest species of bear is the sun bear from tropical south east Asia (the males of this species grow to weigh only 65 kg at the most).
This rule (large animals in a cold climate and small animals in a warm climate) has its exceptions. The most spectacular exceptions are the giant herbivores of Africa. The African elephant is the largest living land animal. It should have problems keeping its body cool. They manage to keep cool by bathing in mud and water, standing in the shade during the hottest part of the day and using their ears as cooling fins. The ears of the elephant have a good blood supply. When the elephant is hot it holds its ears away from its body to catch the air so that the heat is taken from the blood passing through the ears.
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