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
  • Depth, slope

• No correlation with bathymetric
• Correlation with geomagnetics
  • Field gradient minima
• Nonfeeding
  • Minima
• 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?

• Not yet understood

---

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
  • Canada to Mexico
• Generations
• Magnetic material in thorax
• Mexico site
  • Magnetic anomally
• Errors 180 degrees

• Development of magnetite source

--Fig--

---

Bees (Towne & Gould, 1985)

Residual misdirection

--Fig--

• Gravity vs. magnetics

Honeycomb alignment

• With magnetic field line

Timing errors

• Variation in mag field during day