Hi ted40,
You have asked some very interesting questions!
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Why do birds fly in a group?
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Flight
http://www.ornithology.com/lectures/Flight.html
"Many birds fly in flocks. There can be flight aggregations, whereby
birds fly around more or less together but are rarely coordinated -
e.g. gull or terns feeding on a school of fish. A true flock is one in
which the birds are more or less coordinated in one or more flight
parameters: turning, spacing, velocity, flight direction, etc. May be
very coordinated - e.g. shore birds, or very loose, e.g. sparrows,
robins.
Why do birds flock? There are a number of social factors -
reproduction, protection from predators, communication, navigation,
etc. But let's look only at aerodynamic factors for the time being.
One theory is that in coordinated flight flocks such as those of
waterfowl, there's an aerodynamic advantage to flying behind and to
the side of another bird to take advantage of its wingtip vortices.
Logical, and there is some data But if there were an aerodynamic
advantage to flocking, why don't more birds do it? Very hard to study
this kind of behavior."
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Why does it look live a "V" shape?
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Expert Answers Flying Formation Why do birds fly in a V formation?
Brian has been wondering about that familiar V formation used by
ducks, swans and geese ? and occasionally other birds, too ? when they
travel.
http://gorp.away.com/gorp/activity/wildlife/expert/exp090600.htm
"Birds fly in a V to help conserve their energy during migrations.
With the exception of the individual leading the group, each bird
trailing behind the other benefits from a reduction in wind
resistance. The birds are deliberating tailgating each other; it's the
concept of ?drafting,? best known to those gutsy people who drive
close behind semis on the freeway to stay out of the wind and boost
their fuel efficiency.
The next time you see ducks or geese flying in a V, watch them for a
while to see if the lead bird changes. Canada geese do this, and I
suspect other species do, too. Since whoever is up front is working
the hardest, every now and then the birds make a switch. The leader
drops back ? usually all the way back, where wind drag is lowest ? and
a rested bird comes to the front. While there is no single, unchanging
?leader? for a V of birds on the move, it is the oldest, experienced
individuals who are calling the navigational shots, using the sun and
the stars at night to orient themselves and stay on course.
Another thing you'll often notice is how a ?V? changes shape.
Sometimes it looks more like a check mark, with one bird flying lead,
two or three birds trailing on one side, and the majority of birds
strung out on the other. This too is a strategy for dealing with wind.
It usually means a crosswind is blowing ? the short side of the
formation is taking the brunt of the wind, while on the long side, the
birds are attempting to shield one another from it."
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Science Across the World
http://www.scienceacross.org/index.cfm?fuseaction=content.showcontent&node=361
"QUESTION: WHY DO BIRDS FLY LIKE A ?V??
ANSWER: Every bird makes a current for the others while they flutter.
So the other can increase their speed 71% with the help of this
current. If a goose leave the ?V? shape, it can?t fly and has to join
the group again. If the leader gets tired, it goes to the end and the
other becomes the leader. So the process continues. The back ones
shout at the fronts to increase the speed. If one of the geese is
hunted, other two geese lease with it and wait till it dies or
comeovers. Then they join a group to catch their first group."
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Aerospaceweb.org V-Formation Flight of Birds
http://www.aerospaceweb.org/question/nature/q0237.shtml
"Scientists who have studied formation flight believe that birds fly
in this way for two reasons. The first reason is that the shape of the
formation reduces the drag force that each bird experiences compared
to if it were flying alone. This decrease in drag occurs thanks to the
formation of wingtip vortices described in previous articles."
[edit]
"Another theory as to why birds fly in formation is that this
orientation allows the birds to communicate more easily. The V
formation provides the birds with good visual contact of each other to
keep the flock together. This communication minimizes the possibility
of losing birds along the way as the formation crosses vast distances
during migration."
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How do they know a storm is coming?
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Bald Eagle
http://www.learner.org/jnorth/tm/eagle/WeatherBarometer.html
Birds and the Built-in Barometer
"Scientists have long noticed that birds feed intensely as air
pressure falls. They apparently have an inborn barometer that is
extraordinarily sensitive.
Adapted for Survival
This is a handy adaptation for all birds, even non-migrants, because
storms usually are associated with falling air pressure, and birds
have a hard time getting food during a storm. The sooner they can
predict a storm before it hits, the more time they have to prepare.
The ability to sense air pressure is also handy because birds often
migrate along frontal systems, and changing air pressure is one of the
first signs that a front is coming. Just as low pressure indicates
storms, high pressure systems typically have clear skies. So sensing
changes in air pressure enables a bird to anticipate weather changes.
Navigation: What's Your Altitude?
Scientists also have known for a long time that migrating birds fly at
different altitudes than non-migrating birds, and maintain this
altitude even on moonless nights when they can't see the ground at
all. How do they maintain a particular altitude? Many scientists
suspect that this is also due to their ability to "feel" air pressure.
Studies have shown that birds are extremely sensitive to small changes
in air pressure, comparable to differences of only 5 to 10 meters in
altitude. (Atmospheric pressure is lower at higher altitudes. On a
barometer, pressure is lower by 1 cm for every 100 meters of
altitude.)
How do birds sense air pressure? Scientists don't know!
They do have a couple of guesses. One is that birds may be able to
detect it through their inner ear. Humans detect large changes in air
pressure in our own inner ears when we make a fast change in altitude;
that's when our ears "pop." Another guess is that the birds detect air
pressure though the huge air sacs that connect to their lungs and fill
much of the space inside their bodies."
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Colorful northern birds in our storm-tossed yards
http://www.palmbeachpost.com/goodlife/content/home_garden/epaper/2005/11/13/a4k_winging_it_1113.html
"We know that most animals, including birds, sense the drop in
pressure that precedes a storm and seek shelter."
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How do they know to fly south for the winter and when the return back
north for spring?
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The Mystery of Bird Migration
http://birding.about.com/library/weekly/aa032898.htm
"Birds that breed in the northern hemisphere, especially those in
regions with definite seasonal differences tend to migrate, even
travelling down into the southern hemisphere. The Arctic Tern makes
the longest journey, migrating from the North Pole in the fall down to
the South Pole and then back again in the spring. Birds who breed in
the southern hemisphere also migrate. However very few, except perhaps
sea birds, migrate from the southern to the northern hemisphere."
[edit]
"What triggers birds to start off on their journey? How can they
travel such long distances? How do they know where to go? These
questions have mystified people from the earliest times. You can even
find references to it in Aristotle and Homer's writings as well as
references to it in the Bible. And although we have learned much,
there is so much more that we are learning each migration season.
Fall migration allows birds to move to a different location so that
they will continue to be able to find food. In the spring they return
to the places where they will breed and raise their young. It may be
the slant of the sun's rays, hormonal changes, the change of the
weather or other factors that contribute to the birds' urge to migrate
to their other home."
[edit]
"When are the conditions right for migration? The winds must be
blowing in the direction that the birds want to go. Birds will usually
wait until the most favorable weather conditions then set off on their
journey. Ornithologists watch the weather to help predict when large
numbers of birds will be passing through their area. A strong wind in
the right direction will speed the birds on their way. If there are
strong headwinds, the birds' speed will be greatly reduced, therefore
it will need more fat reserves to travel the same distance. Many birds
that encounter storms and strong headwinds perish into the seas. If
these weary birds are over land, they will drop down and land, find
food and rest before continuing.
The route that some birds instinctively take may seem strange until
you look at the winds. For instance, many birds on the east coast of
the U.S., head out to the Atlantic during a fall cold front. The
northwest winds take them on a southeastern course over Bermuda and
beyond. Then they meet the northeast trade winds and make it to South
America. This unbelievable journey will take them over 1,800 miles of
water and will last over 80 hours. But it is actually easier for them
than the land route along the coast, down through Central America, and
then onto their destination in South America. The winds are the key
factor here."
[edit]
"How do birds know which way to go? How do they stay on course?
Various studies have been conducted that suggest that birds use the
sun or stars as guides. Birds may also use the physical
characteristics of the land below, following rivers, shorelines,
foothills and valleys as guides. There is also the "homing" instinct
that has been studied. There have been studies where birds have been
taken in closed boxes to remote locations and released. The birds
found their way back to their colonies. Homing pigeons are thought to
use smell to help navigate."
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Ducks Unlimited Canada
http://www.ducks.ca/resource/general/faq/faq2.html#go
12. How do ducks and other migratory waterfowl know then it is time to
migrate south, and where do they go?
Generally, ducks, geese and other migratory birds know when it is time
to migrate south due to instinct and some clues from their
environment. The length of the days (photoperiod), weather conditions
and reduction in food sources (because snow and ice cover the ground
and water) are good indicators for the birds to begin heading south.
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How close do they usually fly to each other?
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Earth & Sky Radio Series
http://www.earthsky.com/shows/observingearth.php?date=20030107
"Why do geese fly in the formations they do?"
"Geese fly in a variety of formations, ranging from slanted lines to
patterns that look like V's, U's, or even W's. They tend to fly close
to each other, in the same horizontal plane. Flying is a costly way to
move -- in terms of energy -- and these formations help the geese use
their energy better."
[edit]
(More on flock formation)
"Birds riding on updrafts can save about 40% of the energy needed for
lift if they were flying on their own. The leader bird takes time off
rotating with other birds in the flock. Another benefit of flying in a
flock is that the young birds learn the route traditionally taken by
the older, experienced birds."
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how do birds know a storm is arriving
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Best regards,
tlspiegel |
