why do birds migrate? migration is a strategy to take advantage of seasonally abundant food supplies...
TRANSCRIPT
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Why do birds migrate?
•Migration is a strategy to take advantage of seasonally abundant food supplies
•Weather and photo-period are triggers
SNOW BUNTING
DEC
JAN
FEB
MAR
APR
MAY
NOV
OCT
SEP
AUG
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Complete Migration
•All individuals leave the breeding areaafter raising their families
•Most complete migrants breed in temperate northern climates
•Many complete migrants travel incredible distances between breeding andnon-breeding habitats
Cerulean warbler Wilson’s plover Stilt sandpiper
MIGRATION STRATEGIES
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Partial Migration
•Seasonal movement by some, but not all, individuals away from breeding area
•Some overlap of breeding & non-breeding ranges
Red-tailed hawk Herring gull Bewick’s wren
MIGRATION STRATEGIES
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MOON WATCHING
Requires a full moon, a comfortable
chair and binoculars
How dowe study migration?
BANDING
US Fish and Wildlife Service Bird
Banding Laboratory
RADAR (NOAA)
Several years ago, researchers at Cape May
counted 14 million birds in one night
RADIO TELEMETRY
Carl Safina followed a single radio-tagged
albatross throughout its range
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27 192 358 6792,100
4,615
8,094
15,000
32,322
42,868
52,471
0
10000
20000
30000
40000
50000
60000
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
How dowe study migration?
Number of participants 1900-2000
CHRISTMAS BIRD COUNT
52,471
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Anatomy of Flight
• A fused sternum with a “keel” provides the attachment points for the flight muscles.
THE BASICS OF FLIGHT
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A flap is a flap
• Flight feathers are asymmetrical to allow them to change shape during flight• A wing must allow air to pass through it on the up-stroke
THE BASICS OF FLIGHT
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Higher Pressure
LIFT
Eddy = DRAG
Airflow
Lift & dealing with drag
•Lower air pressure above and higher pressure beneath wing creates lift
•During flight, air currents coming off the trailing edge of the wing create eddies which cause drag
Wing cross-section
DEALING WITH DRAG
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Wing slotting
One way to reduce the drag causedby these eddies is to break them up into smaller eddies.
DEALING WITH DRAG
Primary feathers create
smaller eddies = less
drag
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Ground effects
Flying very close (within a wing length) to a body of water allows the rippled surface to absorb the air currents coming off the trailing edge of the wing, reducing drag.
DEALING WITH DRAG
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Powered
•Characterized by continuous flapping
•Results in a level course through the air
•Examples: sandpipers, ducks, geese, rails and hummingbirds
THE BASICS OF FLIGHT
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Bounding
• Birds flap in short bursts to gain altitude, and then descend with wings folded against the body
• Bounding flight results in constant climbingand descending
• Examples: warblers, vireos, small woodpeckers, orioles, robins and tanagers
THE BASICS OF FLIGHT
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Partially powered gliding
• Partially powered gliding birds alternate between flapping their wings and holding them extended
• Small hawks use flapping to fly between thermals
• Examples: cranes, swallows, swifts, pelicans, and shearwaters
THE BASICS OF FLIGHT
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Gliding birds keep their wings extendedand ride rising currents of warm air tostay aloft. They flap only to regain altitude.
Ratio measures horizontal distance to vertical drop
SAILPLANE 60:1
ALBATROSS 20:1
HAWK 10 to 13:1
MONARCH BUTTERFLY 3:1
Gliding
THE BASICS OF FLIGHT
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Route finding
• Birds navigate by: visual landmarks, the sun, moon, stars, and routes learned from other birds
• Birds also have an internal compass which issensitive to the Earth’s magnetic field
• Migrating birds will maintain a true compass heading
MOON
LANDSCAPE
FEATURES
SMELLS
WINDS
STARS
MAGNETIC
NORTH
SUNRISE
WEATHER
UV LIGHT
SOUND
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Birds usually select the mostefficient flight speeds.How fast?
SEMI-PALMATED PLOVER 22-32
BALTIMORE ORIOLE 22-30
BLACKPOLL
WARBLER15-23
28-40GOLDEN PLOVER
30-44BROAD-WINGED HAWK
32-46OSPREY
28-50COMMON LOON
0 50 mph10 20 30 40
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How long?
• Migrants using powered flight regularly cross stretches of open water like the Gulf of Mexico (500 miles)
• Others flap continuously for as long as 70 hours
• Examples: Ruby-throated hummingbird, Wood thrush and Blackpoll warbler
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How far?
NORTH AMERICAN MIGRATION FLYWAYS
Atlantic Flyways
Mississippi Flyways
Central Flyways
Pacific Flyways
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How far?
Red Knot
Flies from Argentina to Brazil,
to the Delaware Bay,
to the Arctic.
7,000 miles
one way
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How far?
Blackpoll warbler
Winter in South America, and fly
to the Caribbean,
and then to northern breeding
grounds.
2,500 to
5,000 miles
one way
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How far?
Hummingbirds
Winter in Central America and
fly as far north as Canada.
Some fly across the Gulf of
Mexico. (500 miles nonstop)
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How far?
Blue-winged Teal
Winters in South America, and
breeds in northern plains
7,000 miles
one way
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Diurnal migrants
•Most birds which rely on gliding or flap& glide flight are diurnal migrants
•The chief benefit of daytime flight is thermals – rising currents of warm air that provide lift
DAY OR NIGHT?
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Nocturnal migrants
•Many birds which use powered flightare nocturnal migrants. Why…?
•Night flying helps birds avoid predators
•Other benefits include calmer, more stable air
DAY OR NIGHT?
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Fat is the currency of migration
•Fat is the most important fuel for migration
•Many species double their weight with fat fuel for migration
Shorebird Songbird Hawk
Typical Body Fat: PRE-MIGRATION
66% 70% 15%
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Fat is the currency of migration
PRE-MIGRATION
(Brazil)
POST-MIGRATION
(Delaware Bay)
RED KNOT BODY FAT
3%
66%
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Re-fueling stations are critical
When a Red Knot arrives at the Delaware Bay,in two weeks it must increase its body weightby 60% to complete the trip to its arctic feeding grounds. The additional weight must be in the form of fat…
A 175 lb man who wants to gain
105 lbs (60%) in two weeks would
have to eat 46 Big Macs per day for
14 days…
…and turn it
all into fat!
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Birds rely on the samere-fueling stations
Stopover places provide abundant foodfor re-fueling needed by shorebirds to complete migration, as well as roosting places.
Copper River
Delta, AK
San Francisco
CA
Gray’s Harbor,
WA
Cheyenne
Bottoms,
KS
Platte River,
NE
James Bay,
Canada
Delaware
Bay, MD
Bay of
Fundy, ME
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Threats to migration
• Loss of non-breeding ranges due to agricultureand seaside development
• The destruction of the tropical and boreal forests
• Habitat fragmentation
The biggest threat to migration is habitat loss
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Everythingin the worldis connected to everything else
•Migratory routes are the invisible lines ofconnection which show us how people,places, and wildlife depend on each other
•Migration tells us about our physicaland spiritual health