Hummingbird Migration Update: April 13, 2000
Latest Migration Maps and Data
The ruby-throated hummingbird migration is quickly approaching the Canadian border--and the first rufous hummingbirds have reached Alaska!
Monarchs and Hummingbirds Race for the Border
Both monarch butterflies and ruby-throated hummingbirds are now traveling across eastern North America, and both are known as nectar eaters. We'd like to know your opinion:
A Sappy Subject: Challenge Question #8
Studies of ruby-throated hummingbirds on migration have shown that their northbound flight isn't timed to match the peak blooming of many flowers that they could feed on along the way. In fact, the hummers often arrive in northern areas up to a month before many such plants have even begun to bloom. But somehow these early birds find enough food to get by. They often depend heavily on tree sap, which is remarkably like nectar in sugar and amino acid content. Here's the question:
(To respond to this question, please follow
the instructions below.)
Brrrrrr! Surviving the Cold
Last week a late-season blizzard hit the Northeast right as hummingbirds were arriving. How do these tiny creatures survive such a cold, unfriendly "welcome?"
It takes a lot of energy to keep hummingbird bodies going. Ruby-throated Hummingbirds' hearts beat over a thousand times per minute when the birds are active. Their wings beat 60 times per second. A hummingbird's body temperature ranges from 102 to 108 degrees. The tiny birds breathe fast too. In his book "The Life of the Hummingbird," Dr. Alexander Skutch's wrote about an excited Anna's Hummingbird (about the size of our Ruby-throat and Rufous) that breathed 273 times per minute!
All this takes a LOT of fuel! And when the temperature is cool, a hummingbird needs even more energy to do the shivering that keeps their body temperature at its normal range. Yet their tiny size means that hummers can't store very much food at a time in their bodies, which have a lot of surface exposed to the cold.
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 hummers 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 so they have the energy to migrate again.
Saved By Torpor
What happens if the weather gets too cold? In the tropics, when the night air temperature drops below about 93 degrees Fahrenheit, sleeping hummingbirds let their body temperature drop to close to the air temperature. Otherwise, their shivering during sleep would use up so much energy that they might not wake up. In April, when they return to North America, hummers 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." Torpor works the same as our lowering the thermostats in our houses at night to save energy.
Hummingbirds aren't in real danger when the temperature is in the mid 30s (F), as long as they had enough food the day before. But when temperatures fall to freezing, these tiny birds 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 they need to eat breakfast right away. That's where YOU can help!
Serve Up Some Help!
Fueling for High Demands
While we're talking about a hummer's energy needs, here are some facts to digest:
1. While hovering, a hummingbird has an energy output per unit weight about 10 times that of a man running 9 mph. This is pretty close to the highest possible output of human energy--and a pace that can be maintained no longer than half an hour. A hummingbird can fly for much longer periods!
2. A man's actual daily energy output is about 3500 calories. The daily output of a hummingbird leading its ordinary life of eating, flying, perching, and sleeping--calculated for a 170-pound man--is equivalent to about 155,000 calories.
3. A normal man will consume two to 2.5 pounds of food per day. If his energy output were that of a hummingbird, he would have to consume during the day about 370 pounds of boiled potatoes or 130 pounds of bread to get enough calories to meet his needs.
Now, it's YOUR turn to serve up a challenge question:
Scientists "Sample" Data; Why Don't You?
Whew! If you're having trouble mapping so many data points, consider taking a "sample" of the data. A biologist's job is to sample a population to learn more about the entire population. Scientists sample data all the time. But first, discuss together:
Awesome Aerial Aviators: Discussion of Challenge Question #5
Last time we asked: "How can hummingbirds hover in one place? How does hovering help a hummingbird?"
Hooray for Team 7B at Iselin Middle School in Iselin, NJ! They had the answer: "It helps the bird get food, and it hovers by flapping its wings at 75 times per minute in a figure eight pattern."
But why the figure 8 pattern? When a bird flaps its wing forward, it creates forces called "lift" and thrust," which move the bird up and forward. Hummingbirds can rotate their wings backward, which creates downward "lift" and backwards "thrust." By alternating flapping their wings forward and backward, the up-and-down forces and forward-and-back forces cancel each other out, so the hummingbird hovers in one place. By hovering, a hummingbird can remain at a flower long enough to suck out all the nectar it needs.
A Tongue That Fits the Bill: Discussion of Challenge Question #6
Last time we asked: "How would you describe the ideal design for a hummingbird tongue?"
Team 7B at Iselin Middle Iselin, New Jersey sent this answer:
"I would describe the ideal hummingbird beak as a long, slender, flexible, and sticky tongue for it to feed off of narrow flowers."
Good thinking! Check out this illustration of a hummer tongue to see how your design stacks up. Bird expert Laura Erickson tells us that hummingbird tongues look like fine thread, but a microscope shows how very complex they are. The tip is fringed, perhaps for lapping up nectar or entangling tiny insects. The length of the tongue is rolled into two tubes. Nectar is either sucked through the tongue like a drinking straw or pulled up by capillary action.
How to Respond to Today's Challenge Questions:
Please answer ONLY ONE question in EACH e-mail message.
1. Address an e-mail message to: email@example.com
2. In the Subject Line of your message write: Challenge Question #7 (OR #8 OR #9 OR #10).
3. In the body of EACH message, give your answer to ONE of the questions above.
The Next Hummingbird Migration Update Will Be Posted on April 27, 2000.
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