Understanding the Incredible Journey of Hummingbird Migration
By Filip Tkaczyk
They are our smallest, most maneuverable, and most vividly colored birds in North America: the hummingbirds. About 18 species occur in north of the Mexican border. There are many amazing things about the natural history of hummingbirds, but perhaps none as impressive as the story of hummingbird migration.
To understand migration, we must first consider how hummingbirds live.
Hummingbirds have bodies designed to gather nectar from flowers. Their tongue is very long, skinny and grooved in the center to assist in reaching nectar deep down inside a flower. Their wings beat very rapidly in a figure 8 pattern in the air, allowing them to fly forward, backward and to hover perfectly in place. Some flowers have co-evolved with hummingbirds, and those flowers are often tubular, thick-walled and have almost no scent. Hummingbirds find flowers via sight, and visit flowers of many vibrant colors, not just red ones. In a behavior known as "trap-lining," hummingbirds will pay a daily visit to a favorite patch of flowers and artificial feeders. Nectar is a high energy food vital to hummingbirds, and it provides important fuel especially during hummingbird migration.
Nectar is not the hummingbirds only source of food, as they also eat a variety of insects. They gather insects in several different ways. Some species will sit on a perch observing their surroundings, then fly out to capture prey in a behavior known as "hawking." Another method hummers use in gathering food is called "gleaning," which involves one of several techniques. Some hummingbirds will flying along branch tips searching for tiny moth caterpillars. Others will fly along the base of branches and along tree trunks searching for insects hidden in the tree's bark. Some hummingbirds will fly near the ground and with an explosive puff of air from the wings, flip over small leaves on the ground. They then proceed to inspect the ground and the underside of the leaf for small insects. Hummingbirds also glean by seeking out fresh sap-wells created by sapsuckers for trapped insects or by carefully pulling insects out of the webs of spiders. Though nectar is higher in energy, insects help provide the birds' protein, vitamin and mineral requirements with which hummingbird migration would not be possible.
It is their dietary needs that force hummingbirds to migrate. In most of the United States, flowers are only seasonally available and so hummingbirds, especially those living in northern states, must migrate south for the colder months.
Each species of hummingbirds migrate for different distances and to different locations. They have been clocked at up to 60 miles per hour in flight. Scientists have shown that hummers stick to the same migration routes each year and often can be seen on the same day at the same location along their migration route each year. Most species of hummingbirds winter south of the US/Mexican border. Though studies in the last decade have shown many species are wintering within the United States.
In the Pacific Northwest, there are 4 species of hummingbirds: the rufous, Anna's, black-chinned, and calliope. The rufous and black-chinned hummingbirds migrate to the southern extremes of the southeastern states, though some of the black-chinned hummingbirds also travel to southern Mexico, where the tiny calliope hummingbird goes each winter. The most unusual of the 4 species is the Anna's hummingbird. Though some Anna's hummers leave during the winter, many stay put! In fact, there are places in Seattle and Portland where they can be seen on warm winter days. They might be one of our most cold tolerant hummingbirds.
The most incredible journey of hummingbird migration is undertaken by some populations of the ruby-throated hummingbird. This species is the main hummingbird species found in summers from the Midwest to the East Coast. In a single, non-stop flight in the fall, they travel across the Gulf of Mexico from the Gulf Coast of the United States, clear across to the Yucatan Peninsula in Mexico. They do this not once, but twice a year! What an exhausting journey it must be for them.
In order to maintain a body temperature of between 104 and 111 degrees Fahrenheit and with a heart rate of between 250 and 1,250 beats per minute, hummingbirds need a great deal of energy. At night, hummingbirds go into a state of suspending animation called "torpor." In this state, body functions are almost totally suspended. The heart rate is slowed to as little as 50 beats per minute and body temperatures can drop down to 55 degrees Fahrenheit!
Cold temperatures during the day will also lead hummingbirds to be less active. If it is low enough, they will go into a suspended state as they would for the night. If a sudden drop in temperature occurs, hummingbirds may have to seek shelter quickly.
Hummingbird migration can be extremely arduous and challenging to hummingbirds. Especially if they have to deal with a sudden shifts in the weather.
I once observed a rufous hummingbird take shelter in a hanging pot of plants on my patio during a late spring hail storm. It was feeding at the artificial feeder next to the plant. It was obvious that it was being effected by the dropping temperatures. As the thermometer dipped, the bird became more and more sluggish in its movements. Eventually it was slumped over on the feeder, looking as if it might fall off. In a last, great gesture it flew to the nearby potted and settled down in the dirt underneath some herbs. Then the hail began to fall. Thankfully, the bird was protected under the herbs and by the overhanging eaves. When the storm passed, the bird regained its energy and flew back to the feeder where it proceeded to stay and feed for over half an hour.
One of the natural world's great odysseys, hummingbird migration is an incredible spectacle to witness and comprehend. To learn more about hummingbirds, check out some of the excellent bird field guides out there such as Sibley's Guide to North American Birds. You can also check out the following website to learn more about hummingbirds:
References: National Audubon Society, The Sibley Guide to Bird Life & Behavior, David Allen Sibley, pages 358-365, published Oct. 2001.