Compiled as a final-year zoology student at the University of Edinburgh, based on the information given in lectures.
Types of compass used by
animals: sun, polarised light, stellar, magnetic.
The use of a sun compass can be demonstrated by experiments
using mirrors to manipulate the sun's apparent position, or by clock-shift experiments
in which an animal is fooled about the time of day.
Scattering of polarised light in the atmosphere
generates light and dark bands perpendicular to the sun that can be used as a
compass by animals capable of detecting polarised light (e.g. Cataglyphis ants).
Experiments in an artificial
planetarium show that the indigo bunting uses a star compass (Emlen 1970).
Magnetic fields provide three types of
information: polarity (north/south), angle of inclination (which varies depending
on latitude), and intensity. Different animals use different types of magnetic
experiments can turn north-seeking animals into south-seeking ones, and vice
mechanisms (Ritz et al 2002): specialised electric sensor systems (in
elasmobranch fish), magnetite particles, radical-pair mechanism (chemical
reactions affected by magnetism, often involving light).
Some migrating birds use
celestial rotation (of stars around the pole) to calibrate a magnetic compass. They
may recalibrate the compass during migration to take into account changes in
magnetic field declination (Gould 1996).
Some species' magnetic
compasses are affected by lighting conditions; others aren't.
Magnetically receptive fibres
occur in the ophthalmic branch of the trigeminal nerve in rainbow trout (Walker
1997); these are also known to occur in birds.
Baker (1980) conducted
experiments on blindfolded students and concluded that humans have an innate
magnetic compass, but Gould & Able (1981) couldn't reproduce this finding.
Maps and mapping mechanisms
Pilotage is finding the way to a
specific destination in a familiar area, which can be done by following
True navigation is finding the way to a
destination when in an unfamiliar area (e.g. homing pigeons).
In true navigation, animal will
move around trying to detect something familiar.
Gould (1986) believed that
bees' ability to find their way directly home when released in a familiar
landscapes suggests the use of a 'map', but Dyer (1991) argued that the bees
were observing distant landmarks (bees released in a quarry, where there is no
view of the surroundings, have difficulty finding their way home).
Distance to a landmark can be
measured by size of retinal image. Gerbils (and humans) can be fooled by
shrinking landmarks but not by enlarging them - long-distance cues are also
If two landmarks are used and
the experimental area is then expanded: gerbils search at the correct point
with respect to one of the landmarks (suggesting they are encoded independently);
pigeons try to match both distance and direction, creating a line on which to
search; humans average and search in the middle (Cheng & Spetch 1998).
In expansion experiments with
several landmarks, pigeons and young children will search in one corner (homing
in on the particular landmark with the highest 'predictive value'), adult
humans will average and search in the centre.
Reliability affects predictive
value of landmarks. Sticklebacks living in stable pond environments primarily
use landmark cues in T-maze experiments; those from unstable river environments
rely on directional cues instead.
Rats in a symmetrical box
initially use geometric relationships to find the goal (they often make a 180°
rotational error), but after many trials they learn to use other cues such as
colour and pattern (Cheng 1986).
Chickadees (food-storing birds)
go primarily by spatial location of feeder, secondly by its colour pattern.
Juncos (non-food-storing birds) use all cues together with no particular bias
Gradient following - e.g. Paramecium that use chemical gradients
to remain in regions of suitable pH.
Trail following - e.g. ants that follow
foraging routes (and can differentiate between one-way and two-way trails),
galagos that urinate on their hands to leave a scent trail, limpets
that follow mucus trails back to resting sites.
Route reversal - remembering a series of
landmarks, and following them in reverse on the return journey.
Butterfly fish use landmarks to
follow a daily route between sheltering sites at night, foraging sites in
morning, and spawning sites at tip of reef in afternoon - they can be confused
by experimentally moving corals.
Course reversal - uses a series of
Disadvantage of route/course
reversal is that animal is tied to a particular route, not necessarily the
Path integration - by addition of
vectors comprising distance and direction.
Cataglyphis ants living in featureless
desert use path integration to find their way home after foraging. They use
polarised light for a compass (they can be confused by placing filters
overhead). Each time the ant changes direction it stops and spins to align
itself. It constantly updates its 'integrator' so it knows where home is - no
need for complex memory. If ant is moved, its idea of where home is will be
displaced, and it will search (in increasing circles) where it believes its
home to be. (Collett 1998)
Fiddler crabs on mud flats orientate
by keeping their bodies aligned with a burrow (an egocentric cue), ignoring
visual landmarks. Females visit different males' burrows and update their
reference point at each one. If threatened, they will bolt for that burrow,
even if there are nearer ones. (Zeil 1998)
Hamsters can perform path
integration. Rotating their environment confuses them, but only if there are no
visual cues and the rotation is too slow for the hamster to notice.
Pigeons are a good model
because they are domesticated, well-researched, and their behaviour can be
studied locally and repeatedly.
Clock-shifting experiments on
pigeons suggest that sun compass is more important than visual cues in
familiar, nearby environments (Chappell & Guildford 1995).
Experiments suggest that
pigeons can use both local and global cues, but local ones are preferred;
however, experiments were done in a very small room.
Homing pigeons appear to use a
variety of cues - visual, olfactory, etc - to provide them with maps and
Pigeons have the advantage of
height - they can look for landmarks on the horizon, and once they know which
direction to head will follow a compass bearing (Chappell & Guildford 1995).
Anosmic pigeons have difficulty
homing from unfamiliar sites (though not from familiar ones). However, the
results of these experiments are dubious because the techniques used were
invasive and unreliable. Manipulation of the olfactory environment produces
predictable orientation changes in pgeons. (Able 1986)
Pigeons develop a preference
for particular cues - "cue hierarchies" (Walcott 1996).
Rearing birds in a particular
environment predisposes them to use certain types of cues, e.g. birds were more
likely to use olfactory information if reared in an exposed roof than in a
sheltered ground loft (Wiltschko et al 1987).
Animals can be identified by
natural markings (e.g. whales' tail fluke patterns), or by ringing, ear/fin
Insects can be painted or have
numbered stickers glued onto them.
Spool-and-line tracking can be
used within a very small area.
Animals can be dusted with
fluorescent dye that leaves trails.
Animals can be tagged with PIT
tags (Passive Integrated Transponders) that register when the animal passes an
antenna - commonly used with fish in streams, but expensive.
Radio tracking can be done
using transmitting collars (e.g. Arabian oryx) or swallowed tags.
Ultrasonic tags can be placed
on sharks' fins.
Satellite tracking is done
using large transmitter packs that send an ID code picked up by satellites -
data is collected using ARGOS system. Used originally on albatross, later on
swans (using lighter packs). Can be used on turtles (but only when they
surface) or on sharks (using reusable tags that float to surface after a
Miniature GPS route recorders
can be used to track pigeons.
Bird migration probably evolved
independently many times. It occurs in tropical as well as temperate species.
Modern migration patterns were heavily influenced by the Ice Age.
Migratory behaviour is
flexible, and may differ even between closely-related species - e.g.
chiffchaffs are long-distance migrants, willow warblers are not.
Migration may be vertical (e.g.
red deer leave alpine slopes for warmer valleys) or horizontal.
Distance and direction in
migrating birds are encoded by an innate circannual rhythm. Birds find their way using a compass and biological clock. Maps
are not essential but may be used by experienced migrants to help maintain
course - displaced adult starlings correct for the displacement; juveniles do
not (Perdeck 1958).
In Gwinner's orientation cage,
willow warblers show north-flying tendencies in spring and south-flying in
Migrating blackcaps change
direction from south-west to south as they pass Spain,
or from south-east to south if navigating down Eastern Europe. This is an
endogenous rhythm. Western (SW-flying) and eastern (SE-flying) populations can
be cross-bred to produce intermediates that fly due south (Berthold 1996).
Photoperiod helps keep timing
of internal rhythm - blackcap's annual rhythm, left to free run, has 10 month
Experienced migrants have
bigger hippocampus (brain area associated with spatial memory) than na´ve
migratory birds (Healy et al 1996) or those that do not migrate.
Migrating birds travel along
orthodromes (the shortest possible curves across the Earth) rather than
loxodromes (direct compass bearings). They achieve this by failing to adjust
their internal clock for longitude (Wehner 2001).
Migration is facultative in
some species (triggered by external factors), obligate in others.
Artificial selection on
partially-migrant blackcaps can produce populations of all migrants or all
non-migrants within a few generations (Berthold et al 1996).
If two clutches of blackcaps
are laid during the summer, the second will undergo far more rapid development
so that they are ready to migrate when winter comes (Berthold et al 1970).
Blackcaps from more northerly
populations show migratory restlessness earlier in year (Berthold & Querner
Migration is preceded by
physiological changes: hyperphagia, fat deposition, changes in diet.
White-crowned sparrows switch
to a fatty diet (seeds instead of insects) when preparing to migrate.
Departure of migrants is
triggered by sudden changes in season.
Hormones such as melatonin (secreted
by pineal organ) and testosterone are involved in control of migration.
How do migrants go without
sleep? Black-crowned sparrows sleep less during migration season, but this
doesn't appear to impair their cognitive abilities, unlike normal sleep deprivation
(Rattenborg et al 2004).
Orientation in salmonid fish
Prior to migration, salmonids
undergo changes in morphology (becoming more slender and streamlined), physiology (heightened osmotic regulatory capability) and
behaviour (switch to negative rheotaxis - swimming downstream).
Migration may be triggered by
photoperiod, seasonal timing and/or temperature.
Crude navigation doesn't
require experience gained on outward journey but more precise homing does.
Salmon released directly into open ocean fail to locate
their natal rivers (Hansen et al 1992/3).
polarised light, inclination of light, magnetic fields and ocean currents have
all been implicated in long-distance navigation in salmonids. In experiments,
celestial cues were primary stimulus, but at night magnetic fields were used.
Young salmon don't respond to polarised light, but some mature ones learn to
(Parkyn 2002). Moore et al found
magnetite particles in salmon. Salmon follow gyres (circular ocean currents)
Short-range navigation to natal
river relies on olfactory cues. Experiments using foreign chemicals (PEA and
morpholine) can mislead fish into particular streams (Scholz et al 1976). Anosmic
fish can't locate their natal streams (Halvorsen & Stabell 1990).
Peaks in thyroxine levels
regulate the timing of olfactory imprinting - controlled by internal
development process and by external cues (exposure to novel smells). Artificial
elevation of thyroxine levels aids imprinting. Juvenile migrating salmon have
higher thyroxine levels than non-migrants (McCormick & Bjoernsson 1994).
Orientation in insects
(Collett & Zeil 1998)
Butterflies use a sun compass
linked to a chronometer - this has been demonstrated by catch and release of neotropical butterflies with clock-shifting (Oliviera et al
1998) and flight simulation with Monarch butterflies (Mourtizen & Frost
Butterflies and other insects
have structures in their eyes for seeing polarised light. The 'e-vector' (a
dark band of polarised light across the sky at 90° to the sun, visible even
through cloud) can be used for orientation - manipulation of e-vector produces
predictable orientation changes in butterflies (Reppert et al 2004).
In the locust Schistocerca, specialised cells in the
dorsal rim area of the eye detect polarisation (Homberg 2002).
Dung beetles, and perhaps
nocturnal moths, can navigate using polarised moonlight.
Some insects fly towards
odours, demonstrating positive optomotor anemotaxis (turning head and body to
move in response to an air current).
The structure of odour plumes
determines speed and shape of flight tracks in moths. Almond moths fly rapidly
and straight up a high frequency plume, and slowly zigzag across a
low-frequency plume (Mafra-Neto & Carde 1998).
Heart and dart moth calibrates
a lunar compass by reference to the geomagnetic field, maintaining a constant
angle of orientation to the moon as it moves across the sky (Baker 1987).
Large yellow underwing moth
navigates using moon and stars on clear nights, and magnetic compass at other
times (Baker & Mather 1982).
Monarch butterflies contain
magnetite, and use a magnetic compass when sun is not visible (Etheredge et al
Honeybees navigate by dead
reckoning using a stored 'goal vector', and also use landmarks along familiar
routes. They may store a series of images of a landmark, viewed from different
distances (Collett 1996).
Length of honeybee waggle dance
provides an insight into their perception of distance. A bee's odometer relies
on optic flow - differences in flying height and visual contrast distort their
perception of distance (Tautz et al 2004).
Orientation in marine mammals
Whales give birth in warm
waters and feed in cold waters. Why? Thermoregulation for calves is easier in
warm water. Calm water is easier for calves to swim in. Killer whales
(predators of calves) remain in cold waters, where there is pinniped prey -
costs of migration would be higher for them because they are smaller.
Migrating in a straight line
may require no more energy than swimming in many directions when feeding.
Opportunity cost of migration -
mother could have spent the time locating best feeding areas instead.
Whales appear to migrate by
following magnetic minima (north-south stripes along the ocean floor), not
oceanic currents or bathymetric features (Walker et al 1992). Anterior dura of
whale contains chains of magnetite.
Most whale strandings occur
where magnetic minima intersect the coastline (Kirschvink et al 1986).
Orientation in turtles
Marine turtles migrate
thousands of kilometres between breeding and feeding grounds.
Lohmann & Lohmann (1996)
showed that turtles swim in a particular direction when exposed to a particular magnetic field intensity. They appear to keep
within the North Atlantic gyre using a 'magnetic map'.
Hatchlings find the water by
swimming towards light, and by using horizontal elevation cues.
Hatchlings entering the ocean
orientate seawards by swimming into waves. Detection of waves relies on
patterns of acceleration (it works in the dark, and can be simulated with
blasts of air).
Hatchlings may imprint on their
natal beach using wave characteristics or chemical cues. Inconclusive
experiments suggest turtles can imprint on sand from strange beaches or on
foreign chemicals (Grassman et al 1984).
Turtles swimming between Brazil
and Ascension Islands may rely on odour plumes (in wind rather than water), but
the fact that satellite tracking shows they follow straight lines suggests not
(Papi & Luschi 1996).
Turtles use vision on land and
when feeding, but it's uncertain how much they use vision in long-range
Navigation by sound in reef fish
Coral reef fish eggs hatch into
pelagic larvae that develop in the plankton then settle back onto a reef.
It was originally assumed that
larvae drift passively with currents, but the fact that they are strong
swimmers, and frequently return to their natal reefs in mark-recapture
experiments, suggests otherwise.
Armsworth (2000) hypothesised
that the fish use sound to find their way back to reefs.
Fish hear using otoliths (dense
ear bones) surrounded by sensory hairs - the sound can be amplified by
resonation of the swim bladder. For detecting vibration at close range, the
lateral line is also used.
Experiments with two light
traps (one noisy and one silent) or two artificial reefs show that reef fish
are attracted by reef sounds (Simpson et al 2004).
Computer models, and
experiments in 'choice chambers', show that fish navigate towards sound far
more effectively when in groups than when alone - consortium behaviour.
Experiments with electrodes in
the brain show that hearing of larvae is sensitive enough to detect particular
reef sounds over 500m away.
Fish conditioned to either
natural or artificial sounds swim towards natural sounds (though the fish in
the experiment were wild-caught and may have been pre-condition to natural
sounds). Fish conditioned to artificial sounds swim towards them, but fish
conditioned to natural sounds show a negative response to artificial ones.
Could the attraction to sound
be an imprinted behaviour? Clownfish can imprint on chemicals, and experiments
show that embryonic clownfish have sufficient hearing ability to allow
potential imprinting on sounds too.
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