Hilton Jr., B. 1994. Migration of ruby-throated hummingbirds. WildBird 8(5)42-45.

(Note: The draft below was submitted to WildBird magazine; the article that actually appeared in print may have been edited.)

If one of nature's greatest mysteries is how and why birds migrate, then surely the seasonal travels of hummingbirds is among the most incredible occurrences in the natural world.

Human observers have always been amazed by cyclic patterns in their surroundings--phases of the moon, the four seasons, the ebb and flow of the tides--but perhaps none has piqued the imagination as much as the unfailing arrival of birds in spring and their equally predictable departure each fall.

Throughout the ages, bird migration has raised many questions. "Where have these birds been?" "Where are they going?" "How do they find their way?" "How do they store enough energy for long trips?" And ultimately, "Why do they do it?"

For me, such questions arise especially when I ponder hummingbirds, those tiniest of birds that appear far too fragile to fly south from North America each autumn and return the following year. But they do it, migrating from as far north as New England and southern Canada down to Central America for every winter season.

I've been studying ruby-throats--the only breeding hummingbird in the eastern U.S.--since 1984. In those ten years, I've captured in nets or pull-string traps a total of 1,190 hummers and have placed on their legs aluminum bands supplied by the U.S. Fish & Wildlife Service. The bands are minuscule--each bears a unique sequence of five numbers printed the same size as the type you are now reading--but they are permanent and allow me to recognize hummingbirds that I recapture in later years.

To be honest, I don't really know for sure that hummingbirds from York go to Mexico or Nicaragua after they leave Hilton Pond in late summer or early fall, but I do know that none of my hummers over winter around York. Most of them move out beginning in late August and I've never had one stay past October 18. Not coincidentally, birders annually report large numbers of ruby-throats gathering in southern Florida and along the Texas Gulf Coast beginning in early September. A few weeks later, by the first of October, observers as far south as western Panama witness the arrival of Ruby-throated Hummingbirds--a species present in the tropics only in winter.

This evidence that "our" hummingbirds go south for the winter is largely circumstantial, but it's also very convincing; no one has ever actually reported a banded Ruby-throated Hummingbird in Central America, but we assume that's where they go. However, no one knows where the wintering populations in the tropics actually spent their previous breeding season; likewise, we don't know if Pennsylvania populations of ruby-throats might go to a different wintering site than their conspecifics from Tennessee or Michigan. It's not surprising that of all the ruby-throats that have been banded through the years by North American banders, very few were ever recovered. When any bird dies, it is probably consumed quickly by natural scavengers; because of its small size, a fallen hummingbird particularly might be overlooked by human observers.

One Ruby-throated Hummingbird I banded at York in 1987 was found dead by Ron Williams at Clover SC, the following spring. Clover is only about 10 miles from my banding station, but this hummingbird had probably flown a thousand miles or more to Central America the preceding fall and made the return trip shortly before it perished in South Carolina. Ron, whose keen eye spotted this banded hummingbird beneath his backyard feeder, provided one more bit of valuable information about ruby-throat movement and longevity.

The only Ruby-throated Hummingbird ever banded and then recaptured and released more than ten miles away from its original banding site was a young male I trapped on September 26, 1991 at Hilton Pond. Ten days later, on October 10, I had an interesting telephone conversation with fellow hummingbird enthusiast Bob Sargent, who lives in Alabama but travels throughout the Southeast capturing and banding "unusual" hummingbirds. As Bob tells the story, he got a phone call from Gina Pearson in Loganville, GA--just east of Atlanta--about a strange hummingbird at her feeder with a bright green throat. Based on her description, Bob thought Gina might be hosting a vagrant tropical species of hummer that had wandered far from its normal range, so he drove for eight hours to Loganville, took one look at the supposedly exotic hummingbird, and realized that the specimen in question was one that had been color-marked with some sort of dye. Bob caught the bird, read the band number, and called the federal Bird Banding Lab (BBL) in Laurel, Maryland, to confirm that I had banded and color-marked this bird at Hilton Pond ten days earlier and 260 miles away.

Bob called me at York, and I was elated to find that my hummingbird color-marking strategy had finally paid off. Hummingbird bands are nearly impossible to see from any distance, so during spring and fall migration, I have special permission to mark hummingbirds with a non-toxic green dye in the breast or throat region. As Gina Pearson and Bob Sargent found out, it's easy to pick out birds with these color spots--which look nothing like the normal dark metallic green feathers of the ruby-throat's back and wings.

By marking my banded birds at York with green dye, I had hoped that someone would notice the extra color and contact the banding lab, thereby providing information about the actual flight paths of migrating hummingbirds. Where the York-to-Loganville bird was bound--perhaps Louisiana, Florida, east Texas, and beyond--is anybody's guess, but now we know at least one Hilton Pond ruby-throat was on a southerly migration route that took it through the Atlanta region.

It will take many more such sightings and/or retraps of banded or color-marked hummers if we want a better understanding of the migratory paths and ultimate destinations of hummingbirds that breed in the continental U.S. Thus, I'm hopeful that folks in the East will be on the lookout every spring and fall for ruby-throats who are wearing a little extra bright green!

Ellie is a hummingbird bander in Oklahoma who realized that her colleagues needed some way to stay abreast of current happenings in their somewhat exclusive fraternity, so she became a clearinghouse for hummingbird news. Every few months, Ellie sends the Hotline out to banders, providing up-to-date information about hummingbird activity around the country. It was from reading the Hotline, for example, that I learned a significant piece of data about hummingbird migration: A ruby-throat that Ellie banded at Grove, Oklahoma, in August 1992 was found dead by Sharon Erickson the following June near Duluth, Minnesota, about 625 miles due north of the banding site--one of the longest known distances traveled by a banded bird of that species.

Ellie speculates that she had captured this bird on its way south and that it died after returning to its breeding grounds in Minnesota. I'm sure most ornithologists would never have known about this "significant encounter" unless Ellie had published an account in the Hummingbird Hotline. For several years, Ellie and her husband Bill covered all costs of this important newsletter, but now Perky-Pet-the feeder manufacturer-sponsors printing and mailing so that "hummingbird professionals" can continue to share their knowledge with other researchers in the Western Hemisphere.

Even more noticeable is the contrast in weight in ruby-throats; adult males typically weigh between 2.5 and 3.5 grams, while females tip the scales at 3.5 to 4.5g. To put hummingbird weights in perspective, it's worth comparing their measures to more tangible items: for example, a paper clip weighs one gram, while 5-cent coin weighs 5 grams. In other words, a male hummingbird weighs two-and-a-half paper clips, or a nickel weighs two male hummingbirds! That any organism so small can carry out all its necessary life functions--including migrating a few thousand miles each spring and fall--never ceases to fill me with awe and near-disbelief.

What may be even more amazing is that in the days before beginning a migration, ruby-throats go into "hyperphagia," a sort of feeding frenzy in which they spend much more time than usual ingesting nectar and small insects. This increased intake of food causes the birds to put on considerable fat, so much so that a 2.5-gram male ruby-throat may nearly double its weight to 4.5 grams or more!

Laboratory ornithologists have calculated that the fat accumulated through hyperphagia is enough to enable a typical hummingbird to fly nearly 600 miles without having to re-fuel. This is significant when we note that some ruby-throats are believed to migrate from southern Florida to Mexico's Yucatan Peninsula-a distance of about 525 miles.

Since there are no rest stops along the way, hummingbirds have just enough energy to make the perilous trip across the Gulf of Mexico. Strong headwinds in the Gulf may prove too much for weaker birds that didn't gain quite enough weight, and hurricanes in the region just at the peak of migration may take a heavy toll on hummingbird migrants. Those that survive the trip undoubtedly arrive in Central America exhausted and exceedingly hungry, so they probably don't have much time or energy to search for food. I'm concerned that deforestation in the tropics--particularly in coastal areas--will wipe out flowering plants that produce nectar needed to revitalize newly-arrived hummingbirds. This is yet another reason that Central American countries need to be encouraged to protect their natural resources.

On our end of the migratory path, it's important that we North Americans also provide and protect suitable habitat for hummingbirds, not just during migration but throughout the breeding season. Urban sprawl and thoughtless commercial development disrupt and destroy natural habitats needed by hummingbirds and other wild species. A lush, grassy lawn is essentially a "biological desert" as far as most organisms are concerned, so property owners who want to attract hummingbirds would do well to put away their mowers and plant a variety of flowering trees or shrubs.

At Hilton Pond Center, I maintain an extensive patch of Trumpet Creeper vine--a plant looked upon by some as a noxious weed. Come summer, my Trumpet Creepers sprout thousands of tubular orange flowers laden with nectar. I call this weedy patch my "hummingbird magnet," and perhaps it is why I've been able to attract, band, and study almost 1,200 Ruby-throated Hummingbirds in the past ten years.

I've learned through my own observations that natural food sources such as trumpet creeper are important in helping hummingbirds stay healthy as they prepare to fly south. We humans may never know all there is to know about hummingbird migration, but as long as we care enough to protect hummingbird habitat, we can continue to learn amazing facts about these fascinating little creatures--the smallest of all migrating birds.