Hummingbird Migration Update: April 2, 1998
Latest Migration Data
Almost 100 ruby-throated hummingbird sightings are included in today's report! If you're having trouble keeping up with the hummingbirds, don't dismay. There are countless ways to use the data. Today's report contains two new suggestions, and other ideas were summarized in our March 19, 1998 Update.
Links to Hummingbird Migration Data
How Many Miles/Day Does the Hummingbird Migration Travel?
Here's a different way to track the migration.
1. Rather than locate each individual sighting on a map, simply put a sticker anywhere on the state/province where a hummingbird was sighted. Record the date on the face of the sticker.
2. After you've received the first 10 or so records from each state/province, calculate an "average first arrival date" for that place.
3. As the season progresses, find places that have the same "average first arrival date". Draw lines on your map to connect these places. Each of the wavy lines you draw is known as an "isopleth". ("Isopleth: A line on a map connecting points at which a given variable has a specified, constant value".)
4. Finally, at the end of the season, measure the distances between the waves and determine out how you would complete this sentence:
Spring Fever for Hummingbirds?
Robins are said travel with the 36 degree isotherm. Is there a similar relationship for hummingbirds?
3. As described in the "Spring Fever" lesson for robins, calculate the isotherm each week.
4. Keep track of the dates of the first 10 or so hummingbird sightings in your selected state/province. Based
on these records, determine the "average first arrival date" for hummingbirds. What is the isotherm on
Discussion of Challenge Question # 1
In our last update, Challenge Question # 1 asked, "How long do you think it would take a hummingbird to fly across the Gulf of Mexico? How long do you think it would take a ship to travel the same distance?"
"Six hours for the hummingbird and 3 hours for the ship," figured Ms. Lobb's students at Hudson Falls Middle School in Hudson Falls, NY. They're going to love this answer!
First the hummingbird's crossing
The shortest distance across the Gulf of Mexico (Yucatan Peninsula to New Orleans) is 500 miles. Since a ruby-throated hummer can fly about 25 mph, that makes 20 hours of flying time. Under good weather conditions, with the wind at their backs, it probably takes hummers and other songbirds about 18 hours to cross. However, it can take 24 hours of non-stop flying if there are headwinds or bad weather. (Luckily, metabolic studies show hummingbirds can safely fly for 26 hours without stopping or refueling.)
As for the ship...
An ocean-going ship like one can only go about 15 miles per hour. So, it would take about 33 hours to make the 500 mile crossing. A hummingbird is faster!
Most migrants arrive along the Gulf coast between 10:00 AM and 2:00 PM, which means they leave the Mexican coast around 5- 6 pm the night before. Overwater songbirds generally fly between 3,000-10,000 ft.--that's almost 2 miles high in the sky! In contrast, over land songbirds generally migrate between 1,500-4,000 ft.
The reason for risking trans-Gulf crossing is time. Some birds do go around the Gulf in the spring--especially those that breed in the western U.S. But most of the eastern breeding birds go across the Gulf. The shortest distance between two points is a straight line, so they reach the breeding grounds faster by going across, even though it is riskier.
Discussion of Challenge Question #2
Besides a ruby-throated hummingbird, what other things weigh 1/10th of an ounce?, asked Challenge Question #2
"A jelly bean," say Ms. Lobb's students. In fact, hummingbirds are so light you could put 10 of them in an envelope and mail the letter with a single stamp!
Surviving the Cold
All this takes a LOT of fuel! And when the temperature is cool, they need even more energy to shiver to keep their bodies at that high temperature. Yet their tiny size means that they can't store very much food at a time in their bodies. And their small size means more surface area exposed to the cold. Imagine trying to keep the temperature of a jelly bean at 108 degrees F when surrounded by freezing temperatures!
These tenacious survivors are used to major changes in spring weather. If they arrive north a bit before real spring, they can survive cold temperatures for at least a while--as long as they have food. Fortunately, their method of migration ensures that they will have at least some food wherever they are. Once they've cleared the Gulf of Mexico, they stop often to eat as they go. When they reach a point where food is just starting to become scarce, they hunker down for a while until food becomes plentiful again.
What happens if the weather gets too cold? In the tropics, when the nighttime air temperature drops below about 93 degrees Fahrenheit, sleeping hummingbirds let their body temperature drop to close to the air temperature. Otherwise, their shivering would use up so much energy while they were sleeping that they might not wake up. In April, when they return to North America, they don't usually experience temperatures in the 90s in the daytime, much less the night! So almost every night while they are up north, they let their body temperature fall to close to air temperature to conserve energy. This is called "torpor," and works the same as when we lower the thermostat in our houses at night to save energy.
Hummingbirds aren't in real danger when the temperature is in the mid 30's, as long as they had enough food the day before. But when it starts freezing, they must shiver on and off all night to prevent their blood from freezing. This takes so much energy that they just barely survive the night. They start shivering hard as they are barely coming out of sleep, and need to eat breakfast right away.
During this critical time of year, hummingbirds are always on the thin edge between death and survival. Your hummingbird feeder may even mean the difference between life and death for one hummingbird, too close to the edge to make it on its own. Hummingbirds give us a lot of beauty and entertainment. It's nice for us to sometimes return the favor.
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The Next Hummingbird Migration Update Will be Posted on April 16, 1998