Emily Dickinson

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

Complete Migration All individuals leave the breeding area after raising their families Most complete migrants breed in temperate northern climates Many complete migrants travel incredible distances between breeding and non-breeding habitats Cerulean warblerWilson’s ploverStilt sandpiper MIGRATION STRATEGIES

Partial Migration Seasonal movement by some, but not all, individuals away from breeding area Some overlap of breeding & non-breeding ranges Red-tailed hawkHerring gullBewick’s wren MIGRATION STRATEGIES

Irruptive Migration Not seasonally or geographically predictable Distances and number of migrants are unpredictable Food specialists leave the boreal forests for more southerly ranges when food isn’t available Pine siskinRed-breasted nuthatch MIGRATION STRATEGIES

MOON WATCHING Requires a full moon, a comfortable chair and binoculars How do we 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

How do we study migration? Number of participants CHRISTMAS BIRD COUNT 52,471

Anatomy of Flight A fused sternum with a “keel” provides the attachment points for the flight muscles. THE BASICS OF FLIGHT

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

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

Wing slotting One way to reduce the drag caused by these eddies is to break them up into smaller eddies. DEALING WITH DRAG Primary feathers create smaller eddies = less drag

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

Powered Characterized by continuous flapping Results in a level course through the air Examples: sandpipers, ducks, geese, rails and hummingbirds THE BASICS OF FLIGHT

Bounding Birds flap in short bursts to gain altitude, and then descend with wings folded against the body Bounding flight results in constant climbing and descending Examples: warblers, vireos, small woodpeckers, orioles, robins and tanagers THE BASICS OF FLIGHT

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

Gliding birds keep their wings extended and ride rising currents of warm air to stay 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

Route finding Birds navigate by: visual landmarks, the sun, moon, stars, and routes learned from other birds Birds also have an internal compass which is sensitive 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

Birds usually select the most efficient flight speeds. How fast? SEMI-PALMATED PLOVER BALTIMORE ORIOLE BLACKPOLL WARBLER GOLDEN PLOVER BROAD-WINGED HAWK OSPREY COMMON LOON 050 mph

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

How far? NORTH AMERICAN MIGRATION FLYWAYS Atlantic Flyways Mississippi Flyways Central Flyways Pacific Flyways

How far? Red Knot Flies from Argentina to Brazil, to the Delaware Bay, to the Arctic. 7,000 miles one way

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

How far? Hummingbirds Winter in Central America and fly as far north as Canada. Some fly across the Gulf of Mexico. (500 miles nonstop)

How far? Blue-winged Teal Winters in South America, and breeds in northern plains 7,000 miles one way

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?

Nocturnal migrants Many birds which use powered flight are nocturnal migrants. Why…? Night flying helps birds avoid predators Other benefits include calmer, more stable air DAY OR NIGHT?

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 SongbirdHawk Typical Body Fat: PRE-MIGRATION 66%70%15%

Fat is the currency of migration PRE-MIGRATION (Brazil) POST-MIGRATION (Delaware Bay) RED KNOT BODY FAT 3% 66%

Re-fueling stations are critical When a Red Knot arrives at the Delaware Bay, in two weeks it must increase its body weight by 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!

Birds rely on the same re-fueling stations Stopover places provide abundant food for 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

Threats to migration Loss of non-breeding ranges due to agriculture and seaside development The destruction of the tropical and boreal forests Habitat fragmentation The biggest threat to migration is habitat loss

Everything in the world is connected to everything else Migratory routes are the invisible lines of connection which show us how people, places, and wildlife depend on each other Migration tells us about our physical and spiritual health

Sources & further reading Ornithology Frank B. Gill, W.H. Freeman & Co, 1995 The Random House Atlas of Bird Migration Jonathan Elphick, ed., Random House, 1995 The Flight of the Red Knot Brian Harrington, W.W. Norton & Company, 1996 How Birds Migrate Paul Kerlinger, Stackpole Books, 1995 The Audubon Encyclopedia of North American Birds John K. Terres, Alfred A. Knopf, 1982 Living on the Wind Scott Weidensaul, North Point Press, 1999

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