Magnetic Orientation
Issues
Land
- Magnetite (Fe3O4)
- Flat, hills, holes
- Rhode Island
Ocean
- Ridges & sea floor spread
- Magnetic bands
- North/South orientation (generally)
- Distinctive fields & gradients
Whales
Problems of study
Strandings (Kirschvink et al., 1986)
- Navigational errors?
- Local minima vs maxima
- Species differences
- Magnetics for migration?
- Seamounts
- Behavioural and ecological
- Magnetite in anterior dura matter
Migration (Walker et al., 1992)
- Whale sightings
- Monte Carlo simulations
- Geomagnetic
- Field intensity, gradient
- Bathymetric
- No correlation with bathymetric
- Correlation with geomagnetics
- Nonfeeding
- Feeding
- Random-slight association
- Behavioural & ecological influences?
Distant migrations (Stone et al., 1987)
- Humpbacks
- Bermuda winter ground
- Tail markings
- Different summer sites
Magnetite
1-100 ng
Industrial pollutant
Hard to detect
Fish
Yellowfin tuna (Walker et al., 1985)
- Tank experiments
- Reinforce/nonreinforce trials
- Natural field/modified field
- Magnetite in dermethmoid bone
- Crystals rotate in magnetic field
- Other fish
- Change in magnetic response
Birds
(Wiltschko & Wiltschko, 1996)
Geomagnetic field of earth reliable
Inclination compass
Magnetic compass in many avian species
Cross equator migrants
--Fig--
Non-migrating birds
- Also have magnetic sense
- Developmental
- Magnetic first
- Other cues later
Maps?
Pigeons (Gould, 1980)
Magnetics and vision
--Fig--
Magnetics as backup for cloudy days
--Fig--
Magnetic anomalies
--Fig--
Butterflies (Jones & MacFadden, 1982, 1985)
Monarchs
- Migratory route
- Generations
- Magnetic material in thorax
- Mexico site
- Errors 180 degrees
- Development of magnetite source
--Fig--
Bees (Towne & Gould, 1985)
Residual misdirection
--Fig--
Honeycomb alignment
Timing errors
- Variation in mag field during day
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