Page 56 - Design in Nature

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The sparrow's heart beats 460 times per minute. Its body temperature is 108 F (42 C). Such
a high body temperature, which would mean certain death for a land creature, is vitally
important for a bird's survival. The high level of energy birds require for flight is generated
by this rapid metabolism.

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108 F (42 C) body temperature and a fieldfare's 109.4 F (43.5 C)body
temperature indicate how quickly their metabolism functions. Such a high
body temperature, which would kill a land creature, is vitally important for
a bird's survival by increasing energy consumption and, therefore, power.
Due to their need for a lot of energy, birds also have a body that digests

the food they eat in an optimum fashion. Birds' digestive systems enable
them to make the best use of the food they eat. For example, a baby stork
puts on 2.2 lbs (1 kg) body mass for every 6.6 lbs (3 kg) food. In land animals
with similar food choices, this ratio is about 2.2 lbs (1 kg) to 22 lbs. (10 kg).
The circulatory system of birds has also been created in harmony with their
high energy requirements. While a human's heart beats 78 times a minute,
this rate is 460 for a sparrow and 615 for a humming bird. Similarly, blood

circulation in birds is very fast. The oxygen that supplies all of these fast
working systems is provided by special avian lungs.