Transcript Bird Navigation

How do Birds Find Their
Way?
What we learned in the last 20
years
Introduction
► Given
the power of
flight, birds are highly
mobile.
► Some species migrate
and travel great
distances.
 Arctic Tern - 12,000
mile journey.
 Manx Shearwater –
Boston to Wales
Previous Studies
► Matthew’s
Sun-Arc Theory
 Birds look at the movement of
the sun and compares angles
and the noon azimuth to
extrapolate latitude and
longitude coordinates.
► Kramer’s
Map and Compass
Hypothesis
 Birds establish a “Map”
(direction to the goal) with the
help of an external reference,
a compass.
Current Studies
► Landmarks
► Stars
► Ultraviolet
Light
► Infrasounds
► Sun
► Magnetic Fields
► Olfaction
Landmarks
► Pigeons
tested using
frosted contact lenses.
► There is some
indication that birds
use landmarks, at least
sometimes.
► Not effective at night.
Stars
► Many
birds migrate at night.
► “Cluster N” – Mouritsen et
al. 2005
► Indigo Buntings seem to use
the northern sky within
about 35 degrees of the
north star.
► Problematic in cloudy
conditions and in Southern
hemisphere.
Ultraviolet Light
► Study
by Parrish et al.
demonstrated birds
can detect ultraviolet
light.
► Effective even during
cloudy days.
► Not readily studied.
Infrasounds
►
►
►
Low Frequency Sounds
(<10 Hz)
Generated by wind, ocean
waves, storms, mechanical
devices, etc.
Conditioned Cardiac
Response
 Pigeons hear less than 2 Hz.
►
Not readily studied
Sun
►
►
►
Sun acts as a compass (angles of
light/shadow)
Birds possess internal circadian
clock.
On cloudy days, Blue-winged Teal
would circle until they got above the
clouds at which time they started to
move in the appropriate direction.
Magnetic Field
► Birds
have
magnetodetection senses
(Mouritsen and Ritz 2005).
 Birds have magnetite near the
beak.
 Cryptochromes in the eyes.
► Exact
mechanism still
unclear.
► Possible problems
Smells
Intact sense of smell is
necessary for goal-oriented
homing of pigeons.
► Olfactory-based
mechanism linked to
piriform cortex.
► Trace gases/ratio of
hydrocarbons at the home
site distributed via winds
may serve as a
navigational cue (Wallraff
2005)
►
Which one(s) do they actually use?
Most early studies on navigation tried to
explain it by one mechanism.
► Orientation and navigation may be due to a
variety of cues
► Path determined primarily by the sun. The
magnetic field assists as a guide (Wikelski et
al. 2004)
►
Does this apply to all birds?
►
Wikelski seems to think so.
 “It's such a simple and
elegant mechanism that I
would say it is widespread.”
►
Species vary in their
navigational ability.
 i.e. Pigeons.
►
Studies largely consist of a
few species and are lab
oriented.
Conclusion
► Despite
all the theories and experiments
dealing with navigation, there is much that
is still not understood about how birds
determine their position in relation to a fixed
goal.
Future Research
► Is
the sun used to calibrate the magnetic
compass? – Cochran et al. 2004
► Extend analyses beyond homing pigeons
and laboratory analyses.
► See how findings compare with other
species (Salmon, Turtles, Sharks, etc).
Questions?