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Oriole Migration Update: April 9, 1998

Today's Report Includes

Migration News and Data

First Baltimore Orioles Arrive on Texas Coast
Stationed on the Texas Gulf coast at Port Lavaca, teacher Harlen Aschen has been on the lookout for the season's first orioles:

"Our rule always has been: Start looking March 15th but don't expect much until the tax has been sent in (April 15th). The fruit on the mulberry trees is just turning from green to white ... when it is ripe there will be orioles and tanagers. (heaa@tisd.net)

And, here are the season's first Baltimore oriole reports:

Map by
Macalester College
Bullock's Orioles Now Traveling up the West Coast
Because Bullock's orioles breed in western North America, many don't need to cross the Gulf of Mexico to reach their breeding grounds. There was an enormous movement of Bullock's Orioles in Los Angeles around March 29:

"The trees in the parks surrounding the playing fields have been taken over by Bullock's Orioles and Western Kingbirds." SteveS@loop.com

But as you look at today's records, you'll find a surprise: A sighting of a Bullock's oriole in Reading, Massachusetts on April 1st. No kidding! The bird was evidently blown off course during migration and ended up on the East Coast. Have a look at the weather maps from late March and see if you can identify the weather system that sent this bird all the way to Massachusetts:

According to the Associated Press, also blown off course recently was a brown pelican which appeared in Arizona--evidently propelled by El Niño winds all the way from the California coast. "They sort of give up and let the
winds carry them," said Janet Witzeman, of the Maricopa Audubon Society.

Current Weather Map
Surface Data Plot, Purdue University
(Click on Face of Map to Enlarge)
Weather and Songbird Migration: Watch the Weather on the Gulf of Mexico
When the next cold front arrives, thousands of songbirds should "fallout" after their long crossing. View the current weather conditions and look for cold

Challenge Question # 5: How do Birds Forecast the Weather?
When they're about to leave on migration, birds don't have access to the WWW. So they can never be completely certain what the weather is like where they're going. But they can judge what the weather is like right where they are. You must be wondering:

Challenge Question # 5
"How do birds sense weather conditions, and know whether good or bad migration weather might be coming?"

(To respond to this Challenge Question please follow the instructions at
the end of this report.)

Discussion of Challenge Question # 3
Last week we asked, "Why do you think most songbirds migrate at night?"

"We think the orioles fly at night because most of their predators would be asleep," suggest Gale and Jessica of Ms Roggow's 7th grade class in Minocqua,Wisconsin

There are almost as many reasons for nighttime migration as there are
migratory birds!

Avoiding Predators
Just as Gale and Jessica suspected, one reason for nocturnal migration does
have to do with predators. A great many different kinds of predators eat
birds, but only one group, hawks, are adapted specifically for
bird-hunting. Hawks have extraordinary daytime vision but, because they
can't hunt at night, migrants can slip by without being noticed--or eaten!

The cooler temperatures and lack of sunlight at night help keep migrants
from collapsing from heat exhaustion. Small birds must flap their wings
very fast, which heats them up enormously. Though they have few feathers
in their wingpits, and the bare skin there allows them to release some of
that heat, they still get hot when flying hour after hour. Another reason
night-time weather is preferred is that daytime winds almost always die
down around sunset. Although larger birds actually use wind to help them
stay aloft as they soar on open wings, little ones must flap hard no matter
what. They have more trouble controlling their direction when the wind is

It takes a lot of food to fuel migration, and by migrating at night,
songbirds can use most of their daylight hours searching for and eating
food. Skipping a few night's sleep to migrate is worth it for them. But
they do need to ensure that wherever they come down in the morning there
will be food. Therefore, the most successful nocturnal migrants are those
that eat the most abundant and widespread foods--especially insects.

Navigation is another reason long-distance many migrants move along by
night. This brings us to another of last week's questions: "How do they
find their way?"

Discussion of Challenge Question # 4

"How do they find their way?"

Many of the songbirds that migrate at night often depend on the same thing
that has helped sailors plot their course through the ocean for centuries:
the stars. Sailors study star charts to set their direction. But birds
can't read, and they certainly don't have charts! How do they learn the

Birds certainly don't think of groups of stars as the Big Dipper or Orion's
Belt. But from the time they are tiny babies in their nest, they do spend
part of their night awake, looking up at the sky--and they notice the
patterns of stars. Have you ever found yourself awake in bed, looking at
shapes on the window? Birds gaze at the night sky, and notice little by
little that stars seem to move in a circle in the sky. All the stars
except one, that is. The one star that never moves relative to the earth
is Polaris, or the North Star. And once birds realize which is the fixed
star, that is the one they use to tell direction In spring, when they head
north, they set their direction TOWARD Polaris. In fall, when they head
south, birds fly AWAY from it.

Do birds understand that it's the earth's rotation that makes stars seem to
move? They probably don't have a clue! But just because they don't
understand WHY the stars seem to move doesn't mean that they can't take
advantage of what they see!

Birds don't JUST use the North Star. One scientist named Stephen Emlen
studied several Neotropical Migrants called Indigo Buntings in a
planetarium. A planetarium is an indoor room with a globe ceiling on which
lights are projected in the pattern of stars and planets. In an experiment
Dr. Emlen did in spring, 1967, the buntings headed "north" toward the whole
group of stars that are within 35 degrees of the North Star. Even if some
of these stars were blocked out, including Polaris, the birds still headed
in the right direction.
It must be important for birds to be able to rely on more than just one
star, because clouds in the sky often block out groups of stars.

Dr. Emlen and other scientists also learned in planetariums that if they
rotate the projector so ALL the stars are facing the wrong direction, the
birds will change to that direction, too. Dr. Emlen also found that if he
changed the whole star system to rotate around another star, Betelgeuse,
the birds switched to that star to set their course.

But some nights are so cloudy or foggy that no stars are visible. Birds
can easily fly above low clouds, but when they can't, many of them have a
back up system--literally a sixth sense. Just like a real compass, many
birds can actually detect the earth's magnetism!

How? Doing very careful dissections, ornithologists discovered that pigeons
have tiny particles of magnetite (a magnetic form of iron) in their brain
tissue. During the past
decade, scientists have discovered that a great many other birds also have
magnetite in their brains--literally a built-in compass!

Although birds have many different ways to find their direction, sometimes
one will still get lost. As you might expect, the ones that get lost most
often are inexperienced young birds. Birdwatchers often get excited when a
rare bird turns up in their area, but this is often just a confused young
bird that has gotten lost. Some of these lost birds never do find their
way to their proper wintering ground in time, but many do get their
bearings and eventually find their way home.

Witnessing Night-Time Migration
Even though it's hard to SEE night-time migrants, you can still witnessed
their passing. This is because they have a lucky habit of calling out notes
throughout their flight. Why? Because they have a hard time seeing each
other, too! Their call notes help prevent mid-air collisions for them,
acting like little headlights for the ears. On good migration nights, you
can stand outside and hear their notes coming down from somewhere in the
dark sky. Listen carefully, and you may start hearing the different voices
of different kinds of birds. Why do you think their migration call notes
are different from their spring songs?

Bill Evans, who works at Cornell University, travels throughout the country
monitoring and recording migration calls. His recordings help him know
exactly what species are migrating when and where, and what kinds of
conditions are the best, and the worst, for nighttime migration.

Dr. Sidney Gauthreaux, at Clemson University, studies nighttime migration
using radar. Examining military and weather radar data, he discovered that
birds migrating over the Gulf of Mexico had declined an incredible 50%
between fthe 1960s and 1980s. This kind of information is very important
for learning what kinds of birds are in trouble, so we can try to figure
out ways to help them.

Three New Migration Lessons Now Online
The following 3 lessons have been included in Journey North Online
Teacher's Manual:

How to Respond to Today's Challenge Question

1. Address an e-mail message to: jn-challenge-oriole@learner.org

2. In the Subject Line of your message write:
Challenge Question # 5

3. In the body of your message, answer today's question.

Don't Forget!
Please include the name of your school and your location so we can credit you properly for your answers.

The Next Oriole Update Will be Posted on April 23, 1998.

Copyright 1998 Journey North. All Rights Reserved.