1. Migration, Orientation, Movements

2. Migration: An annual two-way movement, usually based on seasonality
What is migration?
Migration:
An annual two-way movement, usually based on seasonality
Wintering Area
Breeding Area

3. We have learned about migration from many efforts An example of a “watched” migration: the Broad-winged Hawk
A medium-sized hawk from
Eastern No. America

4. Tracking Migrating Songbirds
One of first successful attempts
to track the migration of a songbird
(Swainson’s Thrush) With a radio transmitter
From Cochran et al Living Bird

5. Radar Also Provides Much Information
Use of radar
Radar detection of birds arriving near Houston, TX
(images from S.A. Gauthreaux, 1999)
Trans Gulf migrants arriving
Apr 25, 0031 GMT
Trans Gulf migrants leaving
Apr 25, 0159 GMT

6. Basic Types of Migration
Obligate annual migration
Latitudinal migration (neotrops)
Elevational
2. Irruptive migration (food highly variable)
Rough-legged Hawks
Snowy Owls
Crossbills
Redpolls
3. Partial migration
Some individuals of a species migrate while
others do not. Adapts to local conditions

7. Differential Migration
Sex and age classes may have different migration characteristics
Example: Dark-eyed Junco (Slate-colored race)
Migrate south to eastern US to Gulf Coast, but migration distances of individual juncos shows different average wintering distributions of males, females, and young.
1. Adult females migrate farthest south
2 young males stay farthest north in Indiana & Ohio.
3. Adult females, young females settle at intermediate latitudes.

8. Fat as fuel for migration
Necessary for long-distance migration
Fat yields 2x as much energy & water as carbohydrates & protein
Migrants fatten rapidly before migration and can add it quickly while feeding at resting points along the way (called stop-over sites)
Stop-over sites are very important for birds crossing vast areas of inhospitable areas (e.g. ocean, large lakes, deserts)

9. Timing of migration Photoperiod
Local conditions (food, vegtation changes)
Weather patterns (cold, warm fronts)

10. Weather That Prompts Migration
In fall, largest flights occur in the southward flow of dry polar air immediately following the passage of a cold front.
In spring, major movements occur in warm southerly air flow on the west side of high pressure centers.
Once airborne, passerines usually fly downwind regardless of wind direction.

11. From Able, K. (ed.) 1999. Gatherings of Angels

12. When migrating over land, songbirds progress in a series of relatively short flights, up to 200 miles or so, interrupted by 3-5 days of rest.
Length of stop-over depends on local weather, how much fat the bird has, and refueling conditions
In one October flight, 500,000 ducks flew from eastern Saskatchewan & Manitoba to Lousiana in a little over 1 day! (=1512 miles; mean ground speed mph)
A flock of Snow Geese flew from James Bay Canada to Louisiana in 60 hours!

13. How Fast Do Migrants Fly?
Most songbirds migrate at about mph in still air
Waterfowl & shorebirds: mph
Tail winds or head winds can drastically impact bird speed and (potentially) survival.

14. Movements are Remarkable
Homing behavior
Homing pigeons that return to their lofts from
Distances of 100’s of miles
Other documented displacements
Migration
Latitudinal
Altitudinal

15. Migratory feats A. Arctic shorebirds White-rumped Sandpiper
Baird’s Sandpiper

16. Migratory Feats
Arctic shorebirds:
Stop-over locations

17. Migratory Feats
Blackpoll Warbler

18. Long-distance migration in Catharus thrushes
From Outlaw et al
Auk 120:

19. Migratory Feats

20. Migratory Feats
Short-tailed Shearwater

21. Importance of Stopover Sites

22. To Migrate (and move about beyond the range of local cues), Birds:
Use a two step process
Consult a map to determine the compass course to their goal
Use a compass to navigate to the goal
(Wiltschko and Wiltschko 2009)

23. Use of Map and Compass Compass mechanisms are relatively well known
Magnetic
Sun
Stars
Combinations
Maps less so
Geophysical gradients
Landmarks
Learned and innate components
Recent Review in Wiltschko and Wiltschko (2009)

24. How Do Birds Navigate? Geomagnetism
Solar storms that disrupt the earth’s
magnetic field, also disrupted
the orientation of Ring-billed Gulls.
A bar magnet interferes with a pigeon’s
ability to return to its loft on overcast days.

25. Birds “see” the inclination of the magnetic field, not its polarity
Direction of arrow in He (natural) or H (experimental) does not matter, it is the angle e relative to p that is sensed
Birds “see” this by photopigments in the eye. “Radical-pair” model suggests photon absorption leads to formation of a pair of radicals (singlet and triplet) with unpaired electrons. Light triggers this and the ratio of single to triplet states depends on magnetic field. Birds compare singlets to triplets using pigments in eye, which form patterns on the retina.

26. moves across sky—requires a clock
Sun-compass orientation
-Not constant
moves across sky—requires a clock
-Not always available
Sun rises and sets rapidly, but is slow to change position around noon
--birds use this information
--because rate of change varies with location on earth, birds also learn to use this mechanism

27. Polarized Light
At sunrise and sunset polarization forms a band at 90° relative to the sun. So, position of sun (and E or W) is noticeable even with clouds.

28. Star compass
The “Emlen cage” for
testing orientation
in birds.

29. Integration of Cues
Magnetic field provides a reference system for linking sun position and internal clock with geographic direction
Young birds rely on sun compass more than magnetic, older birds adjust misinformation from sun compass (in experiments) by consulting magnetic field

30. More Integration
Night migrants set compass with polarized light before star compass is visible
Magnetic compass may also be used at this time
The magnetic, sun, and star compasses are integrated components of a single complex system that provides directional information

31. Landmarks are a Start to the Map
Navigating around the home range, can be expanded to navigate back to a familiar area (homing)
Can be done by route reversal, or better yet by keeping track of direction to home and using compasses to navigate in that direction, then local cues
Seems to only be done by very young birds
Different from migration to a new location (first time migrants)
Older birds use a real map, coordinate based, system

32. What about the Map? Gradients used are not known Geomagnetic field
Olfaction
Gravity
Sound (ocean roar)

33. Compass and Map
Innate (direction to migrate) and learned components are involved

34. Why do birds migrate ?
Temperate Origin: birds escape from the inhospitable climates in the north which negatively impact a bird’s life history.
Tropical Origin: migrants aggressively exploit favorable opportunities. Neotropical migrants are essentially tropical species that temporarily exploit the long days & abundant insects of high latitude summers. (rather than as temperate birds that tolerate the tropics to escape the northern winter)