American Robin Migration Update: March 7, 2000
Today's Report Includes:
Today's Migration Maps and Data
Now you may not think this map shows a meaningful pattern--but think some more: For example, what DOESN'T the map show that you might have expected? Plan to compare robin migration with that of another species, such as monarchs, loon, hummingbirds or orioles. Then revisit your robin map and describe the picture you see, comparing and contrasting with the map of another migratory species.
Robins Reach Home
Compare the pattern on this map to the one above. Why do you think they are so
Announcing JN's 2000 Early Bird Contest!
How long will it take robins to reach the end of the road? Once again this spring, students at Sand Lake School in Anchorage, Alaska will officiate our annual Early Bird Contest, and you're invited to predict when the first robins will be seen in Anchorage. To enter the contest, simply answer this question:
Hello, Sand Lake School in Anchorage!
Sand Lake teacher Mike Sterling added this hot-off-the-press news:
The Early Bird Gets the ______ ?
You probably said worm, right? But an early bird also gets. . .the best territory!
Male robins generally choose the nesting territory (the place where mating and nesting occurs), arriving there before the females. The older experienced males are usually the first to arrive and claim nesting territories. The inexperienced males must settle for second-best sites, which explains the chasing you may see among robins in early spring. Nationwide, banding returns show that about 74 percent of robins return to within 10 miles of their birthplace. Both males and females generally return to the same territory. Together, a male and his mate will defend their breeding territory until fall, while sharing common feeding grounds on nearby lawns, golf courses, cemeteries, pastures, and parks. A robin's territory is usually less than half an acre. (An acre is about the size of a football field.) How could you map your robin's territory? Find out at Journey North's:
Why is a good nesting territory so important to a robin? First, robins need safe
places for building nests and laying eggs. After the eggs hatch, the territory has
to provide food not only for ravenous nestlings, but for the parents as well. In
our last report, we said each young robin may eat 14 feet of earthworms in a two-week
nest life, and earthworms aren't even their main food! How can parents keep up with
the demands of such a hungry brood? Hunting and feeding takes every waking hour.
In the northern latitudes of Alaska, feeding time may extend to 21 hours a day. A
robin makes an average of 100 feeding visits to its nest each day. With that schedule,
there's no time to go far for food--another reason why a good territory is important.
Baby robins sometimes consume as much as 150 percent of their body weight in a 12-hour period, which means a good territory is essential for feeding a hungry family. This makes us wonder:
How Do Robins Find Worms?
Robins spend much of their lives searching for one of their favorite foods, earthworms. Most scientists now conclude that they find these worms by vision, thanks to experiments by an ornithologist named Frank Heppner.
In his experiments, Heppner investigated all the robins' senses. To prove robins use vision, he needed to rule out the other senses robins might use to get information about worms. A list of the equipment he used is provided below. But think about this:
Discussion of Challenge Question #4
Last week we said that a robin's diet during the breeding season (spring and summer in the Northern Hemisphere) was mostly earthworms and soft insects. We asked, "What are the advantages of the diet a robin eats during the breeding season?"
Hirsh and Sian at Iselin Middle School in New Jersey responded: "Sping is the breeding season. At this time they eat earthworms and insects. They need the proteins that are in the earthworms and insects so that their babies grow healthy. The protiens help their cells to properly develop."
The warmer temperatures and increasing hours of sunlight bring the whole food
chain back to life. Earthworms and insects are once again abundant. Luckily, robin
parents with themselves and hungry nestlings to feed do not have to search far for
plenty of good food. The high-protein worms and insects help the baby birds grow
Discussion of Challenge Question #5
"When a robin hunting for food cocks its head, do you think it's listening or looking?"
Students from Peabody School, Washington, D. C. had the right idea. Ms. Murdock sent these answers: "Kasib thinks the robin is looking because he's got to see the worms or he'll pass by the worms. Leigh thinks that the robin is looking because usually they don't have their heads down like that."
Kristina Anderson gets a big "hooray" for sending another important part of the answer: "I think that it's looking because a robin can't move its eyes around in its sockets like we can."
We'll add just one thing: Because a robin's eyes are on the side of the head, robins must tilt the head to see objects directly in front of them.
Everyone who wonders how scientists know that robins use sight and not sound in their search for earthworms will enjoy digging into this week's Challenge Question #7!
You can use the data above to make your own maps, or print and analyze our maps.
How to Respond to Today's Challenge Questions
IMPORTANT: Answer only ONE question in each e-mail message.
1. Address an e-mail message to: firstname.lastname@example.org
2. In the Subject Line of your message write: Challenge Question #3 (or #6 or #7).
3. In the body of each message, answer ONE of the questions above.
The Next Robin Migration Update Will be Posted on March 14, 2000
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