Bird Metabolism
By Dave Hanks
The term metabolism refers to all chemical changes that take place in the cells of the body. The speed and degree that these changes occur can vary greatly from species to species. Animals that fly have greater extremes in their metabolism. Normal body temperature in birds can be as high as 110 degrees – a temperature that would kill us. However, baby birds cannot maintain those high temperatures and so must be brooded until their bodies can adapt.
Flight also requires a faster movement of blood through the body. Bird hearts are large for their body size (Small birds have bigger hearts in relation to body mass). The oxygen and heat demands of flight are great. Ground dwelling birds have an average pulse rate of 70 beats per minute. This rate increases considerably from that low to 615 beats per minute in a hummingbird. Most birds, when active, triple their heart rates.
I have many times witnessed perched birds voiding their viscera just before taking flight. It’s like throwing all unnecessary baggage out before take-off.The tremendous amount of food a bird requires for flight energy makes lightening the body as often as possible a requirement. Also, birds cannot have the luxury of carrying a bladder. Most liquids are re-absorbed by the kidneys, and the rest is the white material passed with the solid wastes.
Flight also prevents the carrying of the extra weight that a fetus possesses. Therefore, it’s natural to construct a nest and deposit the next generation in it encased in hard-shelled eggs. Heat is required for embryo development, and so the eggs must be kept warm, usually by a parent who settles down and snuggles them against her brood patch.
The life styles of birds are a never ending source of fascination!
(A Broad-Tailed Hummingbird – Metabolism at a fevered pitch)
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