Bill Hilton Jr.
(6 July 1986)

Reprinted with permission from The Piedmont Naturalist: Volume I, 1986; published in 1987 by Hilton Pond Press, York, South Carolina USA.

May not be duplicated without express written permission of the author.

Drawing by Russ Rogers © Bill Hilton Jr.

Since I started writing the "Piedmont Naturalist," and especially after last week's column on the co-evolution of Trumpet Creepers and Ruby-throated Hummingbirds, I've received lots of inquiries about this little bird that drinks flower nectar.

The most common question I've heard is whether I can explain why there are many fewer hummingbirds at feeders this summer, and I've been wondering that myself. Last year at Hilton Pond I had captured 39 hummingbirds by the 15th of June, but by that date this season only ten new ones had entered nets or traps. For the preceding two summers, my hummingbirds were lapping up more than a gallon of sugar water solution every seven days, while this year there are only enough birds to consume a quart per week. This substantial decrease in the York hummingbird population supports observations made by my readers, and leads me to speculate on possible causes.

I mentioned last week that hummingbirds are real light-weights in the bird world. When I talk with my students about hummers, I have them get out a nickel and heft the weight. A five-cent piece weighs about five grams and a male Ruby-throated Hummingbird weighs a little less than three grams. As incredible as it may seem, a nickel weighs about the same as TWO male hummingbirds! Female hummers are a bit heftier, tipping the scales at nearly four grams, which probably enables them to store enough energy to produce and incubate eggs.

With such small bodies, both sexes have a real problem in maintaining high internal temperatures of about 110 degrees Fahrenheit. Despite insulative feathers, much of a hummingbird is surface area that radiates away body heat at a rapid rate. Even during summer evenings when air temperatures may drop only to 70 degrees, a hummingbird rapidly burns off the sugars that it consumed during the day, making it difficult to survive the night.

In this situation, hummingbirds conserve available sugars by roosting and lowering their body temperatures as much as 35 degrees in a sort of 12-hour hibernation called "torpor." One cool summer morning I discovered what I thought was a dead male hummingbird collapsed into a crotch in a small tree. I reached for the bird and was surprised to hear it making cat-like mewing sounds. Unable to raise its head or lift its wings, it lay in my hand for several minutes before opening its eyes. I walked into the sunshine with it, allowing morning rays to fall on the bird, and in another few minutes its wings began vibrating slightly. Then, as I lifted it up for closer scrutiny, it exploded in my face and flew off in normal hummingbird fashion.

I suppose this hummer made a bee-line for a patch of Trumpet Creeper or a feeder in someone's back yard. There he could get a quick "sugar fix" and acquire enough energy to restore his daytime metabolism. (Incubating and brooding females, by the way, don't go into torpor; otherwise, eggs and unfeathered nestlings would perish.)

If hummingbirds have this much trouble just making it through July nights, it's obvious they could never last the Piedmont winter. Not only would they lose body heat too rapidly to keep from freezing, but there aren't any natural nectar sources available after the proverbial last rose of summer. The only solution to this problem is to migrate, which is what our local hummingbirds do.

Ruby-throated Hummingbirds breed throughout the eastern U.S. and across Canada. These areas have no winter flowers, but Mexico and Central America do, and that's apparently where most Piedmont hummingbirds go. In early August, hummers enter "hyperphagia"--a feeding frenzy that puts on fat for the upcoming migration. (For this reason, August and September may be crucial times to maintain artificial feeders, especially in drought years like this one when plants may have trouble producing nectar.) The gluttonous hummers nearly double their weight in a few days, males going up to about 4.5 grams and females to almost two grams more than that.

As revealed by recoveries of banded hummingbirds, all North American Ruby-throats use the shortest migrational route into Central America by traveling across the Gulf of Mexico. Our Piedmont hummingbirds first fly south into Florida, and a few may overwinter between the Everglades and the Florida Keys. Most, however, load up once more on plant sugars, gaining back enough weight for the most hazardous part of the journey--a non-stop flight across the Gulf to the Yucatan Peninsula.

At its narrowest, the Gulf of Mexico is about 600 miles of open water; there are no rest areas, no snack bars, no landmarks. Ornithologists have calculated that hummingbirds put on enough fat in Florida to fly about 650 miles, which is sufficient to get across the Gulf. However, if the hummingbird fails to eat enough, or if he encounters a headwind, then it's likely that his engines will sputter out, and he will plunge into the ocean and drown.

You may recollect that last fall, during the peak of hummingbird migration, there were several consecutive tropical storms or hurricanes over the Gulf of Mexico. This suggests to me that our 1986 decrease in hummingbirds may have been caused by bad flying conditions that put many Piedmont hummingbirds into salty seas.

It may be that heavy storms so disoriented the birds that they were unable to find their way back to South Carolina this spring. This year I've recaptured five hummingbirds that I banded two years ago, but maybe they learned the way in 1984. This season I've also handled 13 young birds that I banded last year, but young birds typically migrate early, so perhaps they got into Mexico before the storms hit. It's also possible that some of our York County hummers stay in Florida and that the very cold January killed flowers and any hummingbirds that overwintered there. Of course, we'll never really know the actual cause of the population decline, but we still like to speculate.

There is one other explanation that comes to mind, and it is far more disturbing than thinking that some hummingbirds may have drowned or got lost during migration. First we must remember that Ruby-throated Hummingbirds spend only their breeding season with us in the Piedmont. For about eight months of the year, they are in the tropics, where balmy climate and the lush growth of flowering plants allow them to feed, acquire energy for molt, and prepare for the next spring migration.

Unfortunately, things are not as rosy there as they seem. In Mexico and Central America, tropical rain forests are being logged, slashed, and burned at the rate of up to 75,000 ACRES PER DAY! As they deplete the rain forests, farmers and lumberjacks also eliminate food sources and winter homes for hummingbirds. Many of "our" migratory songbirds are in similar dire straits, with their winter habitats being destroyed at incredible speed. Sadly, the land that is cleared is only good for a year or two of farming or grazing for fast-food beef, and the farmers move on to clear-cut another expanse of forest. These defoliated areas are destined to become the major deserts of the western hemisphere.

I don't intend to use this column as a soapbox, but next time you wonder where those hummingbirds are, mightn't you write a letter to ambassadors from throughout Central and South America, encouraging their countries to set aside rain forests for the benefit of future generations of wildlife and people alike? While you're at it, why not send a copy to the White House and ask the President to convey your concerns to appropriate heads of state.

I'd hate to think my grandkids could never see a hummingbird at Hilton Pond or anywhere else except in museum display cases. We've already lost our Passenger Pigeons and Carolina Parakeets, and our Ivory-billed Woodpeckers and Bachman's Warblers are all but gone.

Isn't it time you and I took a stand and took some action?

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