Presentation on theme: "Why do birds migrate? Migration is a strategy to take advantage of seasonally abundant food supplies Weather and photo-period are triggers DEC NOV JAN."— Presentation transcript:
1Why do birds migrate?Migration is a strategy to take advantage of seasonally abundant food suppliesWeather and photo-period are triggersDECNOVJANOCTFEBSEPMARAUGAPRMAYSNOW BUNTING
2MIGRATION STRATEGIESComplete MigrationCerulean warblerWilson’s ploverStilt sandpiperAll individuals leave the breeding area after raising their familiesMost complete migrants breed in temperate northern climatesMany complete migrants travel incredible distances between breeding and non-breeding habitats
3MIGRATION STRATEGIESPartial MigrationRed-tailed hawkHerring gullBewick’s wrenSeasonal movement by some, but not all, individuals away from breeding areaSome overlap of breeding & non-breeding ranges
4How do we study migration? BANDING US Fish and Wildlife Service Bird Banding LaboratoryRADAR (NOAA) Several years ago, researchers at Cape May counted 14 million birds in one nightRADIO TELEMETRY Carl Safina followed a single radio-tagged albatross throughout its rangeMOON WATCHING Requires a full moon, a comfortable chair and binoculars
5How do we study migration? CHRISTMAS BIRD COUNT52,471Number of participants
6THE BASICS OF FLIGHTAnatomy of FlightA fused sternum with a “keel” provides the attachment points for the flight muscles.
7THE BASICS OF FLIGHTA flap is a flapFlight feathers are asymmetrical to allow them to change shape during flightA wing must allow air to pass through it on the up-stroke
8Lift & dealing with drag Lower air pressure above and higher pressure beneath wing creates liftDuring flight, air currents coming off the trailing edge of the wing create eddies which cause dragEddy = DRAGLower pressureAirflowWing cross-sectionHigher PressureLIFT
9DEALING WITH DRAGWing slottingOne way to reduce the drag caused by these eddies is to break them up into smaller eddies.Primary feathers create smaller eddies = less drag
10DEALING WITH DRAGGround effectsFlying 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.
11Powered Characterized by continuous flapping THE BASICS OF FLIGHTPoweredCharacterized by continuous flappingResults in a level course through the airExamples: sandpipers, ducks, geese, rails and hummingbirds
12Bounding THE BASICS OF FLIGHT Birds flap in short bursts to gain altitude, and then descend with wings folded against the bodyBounding flight results in constant climbing and descendingExamples: warblers, vireos, small woodpeckers, orioles, robins and tanagers
13Partially powered gliding THE BASICS OF FLIGHTPartially powered glidingPartially powered gliding birds alternate between flapping their wings and holding them extendedSmall hawks use flapping to fly between thermalsExamples: cranes, swallows, swifts, pelicans, and shearwaters
14Ratio measures horizontal distance to vertical drop THE BASICS OF FLIGHTGlidingGliding birds keep their wings extended and ride rising currents of warm air to stay aloft. They flap only to regain altitude.SAILPLANE 60:1ALBATROSS 20:1HAWK 10 to 13:1MONARCH BUTTERFLY 3:1Ratio measures horizontal distance to vertical drop
15Route findingBirds navigate by: visual landmarks, the sun, moon, stars, and routes learned from other birdsBirds also have an internal compass which is sensitive to the Earth’s magnetic fieldMigrating birds will maintain a true compass headingSTARSMAGNETIC NORTHMOONSUNRISEWINDSLANDSCAPE FEATURESUV LIGHTWEATHERSMELLSSOUND
16Birds usually select the most efficient flight speeds. How fast?Birds usually select the most efficient flight speeds.1020304050 mph28-50COMMON LOON32-46OSPREY30-44BROAD-WINGED HAWK28-40GOLDEN PLOVERSEMI-PALMATED PLOVER22-32BALTIMORE ORIOLE22-30BLACKPOLL WARBLER15-23
17How 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 hoursExamples: Ruby-throated hummingbird, Wood thrush and Blackpoll warbler
18How far? NORTH AMERICAN MIGRATION FLYWAYS Atlantic Flyways Mississippi FlywaysCentral Flyways Pacific Flyways
19How far?7,000 milesone wayRed Knot Flies from Argentina to Brazil, to the Delaware Bay, to the Arctic.
20How far?2,500 to 5,000 milesone wayBlackpoll warbler Winter in South America, and fly to the Caribbean, and then to northern breeding grounds.
21Some fly across the Gulf of Mexico. (500 miles nonstop) How far?Some fly across the Gulf of Mexico. (500 miles nonstop)Hummingbirds Winter in Central America and fly as far north as Canada.
22How far?7,000 milesone wayBlue-winged Teal Winters in South America, and breeds in northern plains
23DAY OR NIGHT?Diurnal migrantsMost birds which rely on gliding or flap & glide flight are diurnal migrantsThe chief benefit of daytime flight is thermals – rising currents of warm air that provide lift
24DAY OR NIGHT?Nocturnal migrantsMany birds which use powered flight are nocturnal migrants. Why…?Night flying helps birds avoid predatorsOther benefits include calmer, more stable air
25Fat is the currency of migration Fat is the most important fuel for migrationMany species double their weight with fat fuel for migrationTypical Body Fat: PRE-MIGRATIONShorebirdSongbirdHawk66%70%15%
26Fat is the currency of migration RED KNOT BODY FAT3%66%PRE-MIGRATION (Brazil)POST-MIGRATION (Delaware Bay)
27Re-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!
28Birds 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.Bay of Fundy, MEJames Bay, CanadaGray’s Harbor, WAPlatte River, NEDelaware Bay, MDSan Francisco CACheyenne Bottoms, KSCopper River Delta, AK
29The biggest threat to migration is habitat loss Threats to migrationThe biggest threat to migration is habitat lossLoss of non-breeding ranges due to agriculture and seaside developmentThe destruction of the tropical and boreal forestsHabitat fragmentation
30Everything 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 otherMigration tells us about our physical and spiritual health