Transcript Migration: orientation and navigation

N O R
I
O
E
I
T A TN
and Navi
gation
Orientation: The state of knowing your location
Navigation: The state of knowing how to move from your present location
to a specified destination
Its useful to consider an inexperienced individual migrating for the first time,
and doesn’t migrate with more experienced adults w/whom they might learn from
In the 1950s Perdeck banded and
translocated 10,000 starling from
The Netherlands to Switzerland and
documented their migration through
354 recaptures.
Adults move NW from release
site toward the correct overwintering site
Juveniles (first-time migrants)
moved SW the correct direction
if traveling from the captured site
These results demonstrate that adults
shown true navigation (they “home”),
whereas
Juveniles execute a migratory program
termed Vector Navigation
Orientation Cage – for quantifying the intensity and direction of Migratory
Restlessness
Blotting
Paper
Funnel
N
W
E
S
Garden Warbler
- Warbler held at constant 12:12 light regime
- Not exposed to the night sky, but exposed
to the Earth’s normal magnetic field
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But adult birds possess truly amazing homing abilities – how do they do it??
Consider one of the following mechanisms:
(1) Maintain direct sensory contact with the site (see, hear, smell your goal)
(2) Use some sort of random or patterned search in an attempt to encounter
something familiar
(3) Inertial Navigation – your return trip is the opposite of route of the way out;
log turns, distances, etc.
(4) Use a learned mental map to localize your position relying on familiar landmarks
(5) Possess a mental map based not on familiar landmarks but of extensive gradients
that act as analogs of latitude and longitude
Wallraff (1980) – transported pigeons under tightly controlled conditions to
prevent them from perceiving any navigational info:
•Airtight cylinders with bottled air
•Light turned on and off at random
•Loud white noise played
•Cylinders enclosed in magnetic coils that provided a randomly changing field
•Placed on a tilting turntable hooked to a computer that varied tilt and rotation randomly
Pigeons made it back – True Navigation
Currently almost all research is focused on the map and compass model of navigation.
Homing is a two-step process involving a mechanism to identify a spatial position
(map) and another to identify directions (compass).
• Sun
• Star
• Magnetic
• Polarized light
Sun Compass – first discovered by
Gustav Kramer in 1951 working with
starlings in orientation chambers.
To use a sun compass birds must be
able to compensate for the changing
position of the sun – time compensation.
It turns out the sun compass is tied to a
bird’s circadian clock and if their clock is
readjusted they make predictable mistakes
These experiments have been done many times and indicate some peculiarities:
When a clock is shifted in a certain way, they mistake a noon sun for sunrise!!
Animals ignore differences in the sun’s elevation, but consider only its azimuth
direction.
The sun is also the first choice in homing pigeons.
Finally, to use as a compass, pigeons must learn the sun’s path (i.e., rises in the E,
sets in the W). They may use a magnetic compass to assign directions to the sun’s
azimuth
A sun compass is obviously ineffective at night
when many birds migrate.
Star Compass – first discovered by Sauer
(1957) who believed birds were born with a
genetically encoded stellar map
Steve Emlen later working in a planetarium
with indigo buntings in orientation cages
showed this was not true.
Instead, young buntings observe the rotation
of the night sky (Earth's rotation) and learn
the center of the axis of celestial rotation –
Polaris – North Star

Emlen exposing birds to normal and
manipulated skies and changing the
Axis (rotate around Betelgeuse)
Apparently birds memorize the position of the stars in the circumpolar constellations
to select the proper direction
The figure shows that when birds are exposed to the night sky offset from the true
time of night they still migrate the proper direction – if they used the rotational positions
instead they would not
When Emlen used Betelgeuse
as the polestar, birds migrated
the correct directions when
tested under a normal night sky
in fall migration
• All birds grew up w/o see a point
source of light
• Groups b and c where exposed
every other night to normal or
manipulated night sky for two mos.
Magnetic Compass – first discovered by
Merkel and Wilschko in the 60s by putting
birds in orientation cages w/o sun, light, or
star cues.
Helmholtz coils – were used to
vary the magnetic field of the
birds in cages and birds predictably
Vary there pattern of migratory
restlessness
At least 18 spp of birds, including
homing pigeons have shown
magnetic orientation
Unlike our compasses however,
birds do not sense magnetic polarity
but rather sense the Earth’s magnetic field.
We don’t know how (SEE NEXT SLIDE).
At the poles the magnetic
field is strongest and intersects
the Earth perpendicular
At the equator the magnetic
field is weakest and magnetic
field lines intersects the Earth
at 0 degrees
Prediction if using:
Field
Dip
points N dips N
N/S
NE
dip
NE
points S dips S
SW
SW
points S
dips N
SW
NE
Unnatural
occurrence
points N
dips S
NE
SW
Southern
Hemisphere
points N
none
NE
random
“N” = compass direction
N = true direction
• The magnetic compass seems to develop spontaneously in juvenile birds if
they grow up in the proper magnetic field.
• It appears to serve as the back-up compass for many migrants when the sun
is not visible
• And it serves to assign directions to the sun’s azimuth (i.e., provides the
standard reference compass)
A few summarizing generalizations:
• Compasses (and probably maps) are redundant
• Their use is flexible based upon info available, but there would
appear to be a hierarchy of use
For instance, many birds appear to rely on the magnetic compass, but not
pigeons, which prefer the sun and use it to over-ride information based on the
former when the sun is exposed
• Compasses also act to (re)set each other in ways that we don’t understand
• We also do not understand navigation to migratory destinations: is it mostly
vector navigation til the bird recognizes (odor, magnetic field, visual cues?)
its destination? We do not have the answers.