Posted: 6/2/04

Heart Throb

When we think about fundamental rhythmic cycles of life, we are attracted immediately to the ëbigí onesñour calendar days or months, or the cycle of seasons that make up our years. The rhythm that underlies all these, however, and flies most of the time beneath our radar, is the pulse of the heart. At about 60 beats a minute, the human heart cranks out 31.5 million beats per year, over two billion beats in a 70-year lifetime.
Impressive as that is, David Sibleyís Guide to Bird Life and Behavior suggests that the three-ounce hummingbird blows us all awayñboth with the flexibility of its circulatory system and the energy of its mighty heart. Consider:

ï On a cold night, when the bird is resting on a perch, its heart slows down to a semi-conscious torpor, bottoming out at around 50 beats per minute. This would be a great resting-but-awake pulse for most humans.

ï Awake but at rest on the nest, the birdís pulse blisters along at 250 beats per minute.

ï In flight and foraging, the pulse reaches an astounding 1250 beats per minuteñmore than 20 beats per second.

Clearly, as far as hearts are concerned, humans are Mack trucks, and hummingbirds are Maseratis. Our hearts far outlast theirs, but imagine the intensity of metabolism that sustains such a prodigious expenditure of energy! Further, if 1250 beats per minute is the pace for flight, imagine the expenditure of heart-energy during migration, from the northern wilderness to Mexico or beyond!

I am glad our hearts do not run at this pace (except, perhaps, when paying income tax). Though Cupid would be challenged to hit such a small and active target, we can only imagine a pulse off the charts, when the hummingbird falls in love.

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