June 5, 2006 | David F. Coppedge

Hummingbirds: Small Wonders

Do you enjoy watching the world’s smallest birds, right from your backyard?  Susan Healy and T. Andrew Hurly provided interesting tidbits about them in a Quick Guide to Hummingbirds in Current Biology this week.1
    There are 330 species of these small flyers noted for their aerobatics and iridescent colors.  Typically, they weigh a few grams.  The largest is the size of a starling; the smallest (from Cuba) weighs a mere two grams, and is nine centimeters long (mostly beak and tail).  Flight muscles comprise 25 to 30% of a hummingbird’s body weight; “a three gram hummingbird beats its wings an astonishing 50�70 times per second,” the authors exclaim.  Yet all this capability grows from an egg the size of a pea.
  Some species migrate to the Canadian Rockies while snow is still on the ground, yet manage to keep their eggs 25° C warmer than the ambient air.  How?  “They are able to deal with cold temperatures because their feathers provide some of the best avian insulation, with more feathers per inch of surface than other small- to medium-sized birds.”  Furthermore, they can lower their metabolism to a state of torpor to conserve energy.
    Before migrating, they store 72% of their weight in fat, more energy efficient than carbohydrate.  This requires some physiological fine-tuning on the inside:

They have the most metabolically active liver known, with the highest levels of enzymes for lipid synthesis along with extremely high rates of intestinal glucose transport, which results in very dilute excreta, invaluable for a nectarivorous animal ingesting large quantities of water in its food.  Quite how they are able to produce highly dilute urine is still not known, but it appears that their renal morphology and physiology is more like that of nectarivorous bats and freshwater amphibia than that of non-nectarivorous birds.

Their hovering ability is well known; they can even fly upside down and backwards.  This is made possible by “a wing structure unlike that of any other birds, which articulate their wings from shoulder, elbow and wrist: hummingbirds’ wings articulate only from the shoulder.”  In the ecology, they fulfill important roles as pollinators.
    Another hummingbird feat that has come to light recently is their skill at memory.  The article states that they “appear to remember where they have visited hummingbird feeders along the way: the reminder for garden owners to put the feeder containing sucrose solution out is often a bird hovering around the place the feeder was hung the previous year” (a reminder not to disappoint the little backyard friends).  “Secondly, they have been shown to remember information on a more local scale, avoiding flowers they have recently emptied and returning to flowers they have left still containing food” (see 04/05/2006, bullet 9).
    How is this all possible in such a tiny creature?  The authors remark, “Although the rufous hummingbird has a brain approximately the size of a grain of rice, it puts it to rather good use.”

1Susan Healy and T. Andrew Hurly, “Quick guide: Hummingbirds,” Current Biology, Volume 16, Issue 11, June 2006, pages R392-R393, doi:10.1016/j.cub.2006.05.015.

Buy a hummingbird feeder and use it as a teaching opportunity for your family.  Hold up a stuffed bird of similar size and weight and ask your kids how many systems would need to be added to make it fly like a real hummingbird.  Imagine NASA designing a remote sensing, guided hovercraft with a computer the size of a grain of rice, able to extract energy from sugar water and fly to snowy peaks in Canada.  Then imagine them making it able to reproduce itself through pellets the size of a rice grain.  Moments like these can help teach young people not to take the wonders of nature for granted.

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Categories: Amazing Facts, Birds

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