Why do animals navigate?ReproductionFood and other resourcesAvoiding inclement conditionsFinding ‘home’
An ultimate question
Navigational StrategiesTrail following/route learningPilotingPath integrationCompass navigationMap-and compass navigation
Trail following/route learningTrails may be visual
(e.g. deer trails)Olfactory (e.g.
pheromone trails in ants)
Niko Tinbergen (1907-1988)Nobel prize for Physiology or
Medicine (1973)PhD Thesis (32 pages long!) on
navigation in digger wasps (‘Beewolves’)
Path integration“Dead
Reckoning” Know direction
& Distance and calculate position from there
Long way out, short way home
How do they know which direction they’ve gone? ‘Compass’ based on visual cues
Celestial Sun position Polarised light
Star compassesNocturnal migrating/flying birds
Seabirds (some) migrating song birds
Experiments Raise birds so they can see night
sky, but not landmarks Raise birds in planetariums with
weird star configurations
Polarised light
The direction from which this polarised light comes indicates the direction of the sun
Fig. 17.6a
Polarised light
Polarised light means you can tell where the sun is even on a cloudy day!
Fig. 17.6b
How do insects see polarised light?
Ommatidium
Aligned Rhodopsin molecules
Dorsal rim of Compound eye has particular ‘focus’ on polarised light
Magnetic fields: organisms can detect them!
Magnetic bacteria use ‘magnetosomes’ to orient to magnetic fields
How do animals detect magnetism? I TroutMagnetite crystals associated
with specialised cells in nose of trout If blocked, magnetic sense
disappears
How do animals detect magnetism? II - Birds Evidence that the nose is required for
magnetoreception in pigeons cf. magnetite in trout nose
Previous studies that blocked nose may have been blocking magnetoreception, not smell…
Most evidence suggests that magnetoreception = ‘map’ rather than ‘compass’ in birds
How do animals detect magnetism? III Birds (again)Resonant molecules?Some evidence from birds that
light-affected molecules (e.g. rhodopsin) might return to unexcited state at different rates under different magnetic conditions Some magnetoreception is light-
dependent
How do animals detect magnetism? IIIa: FliesA blue-light receptor is
necessary for magnetoreception Gene identified, knockout flies
don’t respond to magnetic fields
How do animals detect magnetism? IV: SharksAre known to swim in straight
lines across long distances of open ocean
Can detect electricity Ampullae of Lorenzini
Is electromagnetic induction as they swim generating currents they can detect?
Map and compassMany animals have a visual (or
olfactory) map of their surroundings, which they combine with a compass to allow them to navigate.
Navigational StrategiesTrail following/route learningPilotingPath integrationCompass navigationMap-and compass navigation