Migration Orientation Movements What is migration Migration An

Migration, Orientation, Movements

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

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

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. 1967. Living Bird

How they tracked the migrating thrushes. Now use satellite transmitters Photo-sensitive micro data loggers Isotopes From Cochran et al. 1967. Living Bird

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

A. Nocturnal exodus of birds from stop-over locations in South Carolina B. Same data superimposed on habitat types from Landsat satellite imagery. Highest bird densities were in hardwood forests, not the predominant pine woodlands. From Gauthreaux & Belser 2003: Auk 120: 266 -277.

Basic Types of Migration 1. 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

Resident vs migratory species Generally, birds that migrate to the tropics survive the winter better than do those that stay in the temperate zone. Life history traits Trait Temperate Resident Migrant Tropical Resident Productivity High Moderate Low Adult Survival Low (2058% Moderate (50%) High (8090 %) Juvenile Survival Low Moderate Mod High

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.

Fat as fuel for migration Fuels for migration Fuel Energy Yield Fat Carbohyd. Protein 38. 9 17. 6 17. 2 Metabolic Water (g) 1. 07 0. 55 0. 41

Fat as fuel for migration • Necessary for long-distance migration • Fat yields 2 x 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)

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

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.

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

• 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 41 -50 mph) • A flock of Snow Geese flew from James Bay Canada to Louisiana in 60 hours!

How Fast Do Migrants Fly? • Most songbirds migrate at about 20 -30 mph in still air • Waterfowl & shorebirds: 30 -50 mph • Tail winds or head winds can drastically impact bird speed and (potentially) survival.

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

Displacement of Selected Seabirds Illustrates Homing Ability

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

Migratory Feats • Arctic shorebirds: • Stop-over locations

Migratory Feats Blackpoll Warbler

Long-distance migration in Catharus thrushes From Outlaw et al. 2003. Auk 120: 299 -310.

Migratory Feats

Migratory Feats • Short-tailed Shearwater

Importance of Stopover Sites

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)

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)

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.

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 (likely cryptochrome 4), which form patterns on the retina.

Cells in pigeon brain respond to magnetic field to computationally derive the bird’s position and directional heading. The geomagnetic vector elevation component could provide the bird’s latitude (Fig. 1), the vector azimuth component could be used as a magnetic compass to provide heading direction, and the vector magnitude could provide spatial position cues through local variations in intensity (Fig. 1) relative to a learned internal model of geomagnetic space (4, 7, 24). How MR cell information is used for orientation and navigation remains to be discovered. Wu and Dickman 2012 Science

• In summary, we have shown that single vestibular brainstem neurons encode the direction, intensity, and polarity of an applied magnetic field; consistent with a ferrimagnetic particle receptor (21), as opposed to a radical-pair cryptochrome mechanism (14). • Mourtisen 2018 (Nature 7 June) claims radical pair mechanism most likely. – Neural integration of cues and responses likely occur in NCL, Cluster N (magnetic sense only), and Hippocampus.

• Birds can determine longitude (E – W) by determining degree of difference between magnetic and geographic north (Chernetsov et al. Current Biology 2017)

Sun-compass orientation -Not constant moves across sky—requires a clock -Not always available -Learned 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 (azimuth is cue)

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. • Light scattering by molecules in atmosphere

Star compass (another learned compass) The “Emlen cage” for testing orientation in birds.

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 (requires 7 clear days to learn) more than magnetic, older birds adjust misinformation from sun compass (in experiments) by consulting magnetic field • Hippocampus and NCL likely important brain areas

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

(Mortenson 2018)

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)

Intraspecific, genetic Approach Population founded from South, Likely then developed migration Tropical origin of migration behavior suggested Time of divergence suggests southern populations were original and northern expansion followed retreat of glaciers about 18000 years ago (Mila et al 2006)

Migration May Constrain Brain Size • Large brains are metabolically expensive • Weight counts when you migrate • Sedentary birds typically have larger brains than migrants • Which came first? • Big brain > behavioral flexibility > no need to migrate? • Put another way, Small brain > not flexible > need to migrate • OR Compare timing of evolution of migration and brain size within 1 species, the White-crowned sparrow • Sedentary behavior > big brains > to enable behaviorally flexible strategies that promote survival (Pravosudov et al. 2007)

Big brains came after shift to sedentary habit, not as a precursor Older, migratory subspecies Recently evolved, sedentary subspecies (Z. i. nuttalli) Side bar: Migratory subspecies has larger hippocampus and reduced size of remainder of telencephalon --selection works to fashion different parts of the brain

Hazards of Migration Birds killed by television transmitter at Madison, Wisconsin Sept. 7 -8 and 13 -14, 2005. Tower is 1, 000 ft tall.