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Migration

 I.                     Early (and current) questions

a.     Do birds hibernate or migrate?

b.     Aristotle knew that cranes moved, but thought small birds hibernated

c.      Until 1600s Barnacle Geese in Europe were thought to arise annually from barnacles.

d.     We now know that no birds hibernate, although some go into torpor at night (hummers and even vultures (see recent paper in Condor).

e.     We still don’t know where all species go—are tropical birds austral or northern?

f.        Routes are still not well known for many species - male peregrines

 

II.                   What is migration?

a.     Seasonal/periodical movement between two locations

b.     usually annual - summer vs. winter

c.      can be seasonal - dry vs. wet

d.     usually latitudinal

e.     can be altitudinal

 

III.                  Do only birds do it? – no: whales, caribou, monarchs

 

IV.               Contrast nomadic irruptions

a.     Red Crossbills – nearctic

b.     Ruddy Quail Dove

c.      Toucans

 

V.                 Patterns

a.     Highly varied

b.     usually n-s, esp. in New World because

                                                              i.      flyways are oriented that way

1.      rivers

2.      mountains

3.      coasts

                                                            ii.      summering grounds n. of wintering

c.      Old World often e-w, then n-s

                                                              i.      Alps

                                                            ii.      N. Sea coast

                                                          iii.      Mediterranean

d.     Tropics to temperate

e.     Temperate/arctic to temperate/arctic

                                                              i.      Swainson’s Hawks

                                                            ii.      Sanderlings (some)

                                                          iii.      Terns

 

VI.               Who migrates?

a.     5 MMM birds of 187 spp in Europe and Asia

b.     5 MMM birds of > 200 spp in N.A.

c.      Some S. Hemisphere species go north, but relatively few

 

VII.              Routes can reflect recent distributional changes

a.     Northern Wheatears from UK go back and migrate to Africa

b.     Colonists to Alaska from Siberia go back and vice versa

 

VIII.            The 64K question - Why migrate?

a.     The proximate answer’s easy: daylength shortens

                                                              i.      but not all birds migrate

                                                            ii.      need suite of other factors

                                                          iii.      the ultimate answer is far more complex and one of the most challenging questions in ornithology

                                                           iv.      need to formulate sequence of evolutionary steps

                                                             v.      why do some popns migrate and others not

1.      leapfrog migrations

2.      Sanderlings-some winter in NW NA, others Chile

                                                           vi.      Evolution

1.      populations gain or lose habit (examples)

2.      polymorphism - European Robin

a.      resident pop’s eliminated

3.      individuals in a sp. differ-Juncos a good example

a.      males need to get back to breeding grounds-travel intermediate distance

b.      females - adults go furthest-avoid competition with others that go shorter distances

c.      young - mortality high on migration, go shortest, especially young males

IX.               Feats

a.     25,000 km Arctic Terns

b.     Lesser Yellowlegs -  3220 kms/6 days

c.      radar studies helped figure out small birds’ habits

 

X.                 12 MM birds over Cape Cod one night - heading off for 80-90 hr flight

a.     same as human running 4-min miles for 80 hrs

b.     burning gas instead of fat - 720,000 mpg

c.      once thought hummers couldn’t make it, but calculations were wrong.

d.     Wheatears from Greenland cross 2-3000 km of ocean w/ no help from winds

e.     Leaving Europe, birds cross1100 km of Mediterranean and then 1600 km across Sahara

 

XI.               benefits must be substantial because costs very high

a.     energy costs

b.     exposure

c.      exhaustion

d.     predation – “natural” and human

e.     50% small landbirds in N.A. don’t return

f.        40% N.A. ducks don’t return

XII.              what could benefits be?

a.     previously couched in neg. terms

                                                              i.      avoid starvation

                                                            ii.      shortage of nest sites

                                                          iii.      competition for food

b.     but why not exploit temporary opportunities?

                                                              i.      hummers, tanagers, warblers are really Neotropical birds that move north to the temperate zone to breed

                                                            ii.      not common in African tropical birds – deserts in the way?

                                                          iii.      does occur in SE Asia & India

 

XIII.            Fuel – fat

a.     2 xs the energy & H20 as carbs

b.     fat deposited in adipose tissue, mostly subcutaneous

c.      Blackpoll Warblers & hummers double their weight

d.     refueling necessary for long-distance migrants

                                                              i.      strategic sites essential for conservation (Map)

 

XIV.          Flight ranges

a.     birds loose about .9% body weight/hr (my losing 1.8 lbs/hour) calculations depend on fat load, head/tail winds, water loss or balance

b.     small birds 2,500 km in 100 hrs w/ 40% fat build-up (unless headwinds)

c.      Dunlin 3-4,000 km

d.     small birds from US northeast will backtrack to land if they meet headwinds

e.     coast on tailwinds- i.e. groundspeed doesn’t speed up with a following wind

 

XV.           Timing

a.     accuracy well known

                                                              i.      swallows at Capistrano

                                                            ii.      raptors

b.     internal rhythms

                                                              i.      zugunruhe

                                                            ii.      hormones & daylength but not well understood lengthening daylength in winter stimulate

1.      zugunruhe

2.      hyperphagia

3.      adipose tissue deposition

4.      shortening day in summer triggers:

5.      photorefractory period in gonads

6.      pre-basic molt

7.      hyperphagia & adipose tissue deposition

8.      sex hormones not directly involved, castrated birds follow the typical pattern

c.      weather

                                                              i.      American Robins & Can.Geese follow spring thaw

1.      Fronts

2.      fall migration favored after low pressure system passes

3.      spring in front of a high pressure system differs for sexes (sometimes)

a.      Ospreys

b.      Red-winged Blackbirds

XVI.          night or day?

a.     raptors & soaring birds & swallows by day –

                                                              i.      thermals or feed on the wing

b.     small birds at night

                                                              i.      less predation

                                                            ii.      more favorable flight conditions

1.      nocturnal air less turbulent

2.      lower temperatures reduce heat loss and water retention

3.      refuel by day

XVII.        altitude?

a.     700-800 m most small birds

b.     can be as high as 7,000 m

XVIII.       Gauthreaux’s radar studies

a.     1940s birds showed up in radar in UK during war

b.     1957 US set up WSR-57 radar to track weather - 2” beam

c.      Modernizing in early 90s with WSR-88D doppler radar

                                                              i.      1” beam - higher resolution

                                                            ii.      more powerful - increased range

                                                          iii.      doppler - direction & speed!

                                                           iv.      calibrate with observations across moon

                                                             v.      demonstrates

1.      declines 50% from 65-67 vs. 87-89

2.      habitat preferences/priorities for conservation

3.      roost areas (non-migratory)

4.      important for bird strikes at airports

  Connectivity: Black-throated Blue Warblers

 

Study of American Redstarts

XIX.          Navigation

a.     need?

                                                              i.      find nests

                                                            ii.      find food sources far from nest

1.      nectarivores/frugivores

2.      colonial nesters

                                                          iii.      find, and return from, wintering grounds

                                                           iv.      get home after accidental displacement

                                                             v.      storms

                                                           vi.      ornithologists

1.      Manx Shearwater

2.      White-crowned Sparrows moved from San Jose

b.     how do they do it?

                                                              i.      various senses

1.      system of fall-backs

2.      easiest first, then next, etc

3.      Visual landmarks

4.      solar compass

5.      stellar compass

6.      sense of smell

a.      petrels - good evidence

b.      pigeons - conflicting evidence

7.      geomagnetism

                                                            ii.      elements of learning

                                                          iii.      genetic component

                                                           iv.      the map component

1.      magnetic field?

2.      solar cues - depends on very accurate internal clock

c.      experiments

                                                              i.      opaque glasses

                                                            ii.      release birds on cloudy vs sunny days also clock shift

                                                          iii.      raise birds in planetaria - osprey story on radar tower

                                                           iv.      translocate birds to novel places

                                                             v.      "smellectomy" - petrels find their own nesting material

                                                           vi.      magnetic helmets - and magnetic field in metal cages

                                                         vii.      displace young and adults - adults found wintering grounds, young just went by direction

                                                       viii.      hybrids between populations with different migratory habits have intermediate behavior  

REVIEW QUESTIONS

Is migration just a matter of head south in the fall and back north in the spring? Explain.

What evidence supports the use of visual landmarks?

Use of the sun as a compass requires what additional knowledge?

Describe an experiment in which the use of a sun compass was established.

What evidence supports the conclusion that birds use geomagnetism for orientation?

Do birds use olfaction for navigation? For orientation? Give examples.

What evidence suggests that birds learn how to navigate?

If a young bird were exposed to a stationary sky in a planetarium, would it later be able to navigate by the stars?

Is accurate compass orientation alone sufficient for migrating to wintering territories? Explain.

What internal cues control migratory behavior?

What evidence supports a genetic component to the internal control of migratory behavior?

How does the quality of winter territory affect reproductive success?

How is true navigation different from "clock and compass" orientation? Which do 1st year migrants use? Adults?

What do we mean by "connectivity" when discussing bird migration? How can this be studied?

Distinguish between ultimate and proximate causes of migration.

Do all members of a local population migrate together? To the same places? At the same time? Why or why not?

VOCABULARY:
Migration
Navigation
Orientation
Photorefractory period
Leapfrog migration
Zugunruhe 
Emlen funnels (used to demonstrate zugunruhe)
Hyperphagia
Adipose tissue

 

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