Transcript Bird Navigation - Model Research

Bird Navigation
Tony Ludlow
[email protected]
www.modelresearch.com
12th Jan 2006
Aims of lecture
• Show what birds achieve
• Discuss views about how they do it
• Illustrate the way various systems interact
and how birds calibrate one system from
another
• Review mistakes in the progress of
research
Types of navigation
• Piloting
• Compass sense
• True navigation
Piloting
• Difficult to rule out, given height at which
birds fly
• Not possible for Bronze-winged cuckoos
• Other methods can be demonstrated
Compass v true navigation
• Perdeck’s experiments
• Tracking birds
Perdeck (1958)
Michener and Wallcott's pigeon
harness
Combination of methods
Michener and Wallcott (1967) tracked single
pigeons and found
1. A phase of straight flight, not usually
towards home: compass sense
2. Flight heading accurately towards home:
true navigation
3. Use of landmarks within 10 miles of loft.
Michener and Wallcott (1967)
tracks
Sensory cues:
problems in research
• Circular statistics
• Redundancy not understood (Pennycuick,
Matthews)
• Vanishing direction
• Piloting cues not eliminated
Kramer (1957)
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Starlings --- day migrants
Circular cage – recorded from each perch
Birds showed migratory direction
Confused by overcast
Adjusted for sun movement (90 degrees in
6 hr)
Sun compass: Kramer (1957)
Kramer (1957)
a) Compensated for normal sun movement
b) Followed sun when it was shifted by
mirrors (so not magnetism, etc.)
c) 6hr clock shift caused 90 deg shift
d) `Sun’ kept stationary; birds changed their
angle to it.
Stellar compass
• Sauer and Sauer (1955) showed blackcaps
chose correct autumn directions under a
planetarium and reversed direction in spring
• Emlen (1970) showed that indigo buntings
respond to celestial rotation; they were taught to
use other constellations as `north’ star
• Bellrose (1967) used radar to show that
migrants were well oriented at night, even in
overcast
• May be they see glimpses and keep straight
using the direction of wind gusts (Nisbett, 1955)
Magnetic compass
• Rejected in 1960s
• Evidence in bees (eg. Lindauer and Martin,
1972)
• Keeton (1971) showed magnets confused
pigeons under overcast (could act on compass
or true navigation)
• Wiltschko and Wiltshcko (1972) showed that
robins responded to the angle of dip if strength
of field similar to earth's
• Wallcott and Green used electric coils on
pigeons. NUP disoriented, SUP did not.
Polarised light
• Brines (1980) demonstrated that rotation
of polarised light was used during day
• Seems to be this rather than the sun which
is used
• Birds use rotation of stars to find north
• Using rotation, they don’t need a clock
True navigation
• Perdeck's adult starlings showed true
navigation
• So did Michener and Wallcott's tracks
• The vanishing direction is easy to measure
but very often wrong.
Theories of true navigation
• Every twist and turn is integrated (spider,
millipedes, Walraff (2000))
• Celestial cues could be used to find home
direction (Board of longitude prize)
• Magnetic variation across earth's surface
• Odours
Celestial navigation?
• Requires astonishing accuracy of time
sense
• Requires astonishing accuracy of visual
discrimination (frosted glass contact
lenses)
• Keeton showed that pigeons home when
they cannot see the sun
• After a time shift, pigeons show compass
errors not errors in home direction.
A magnetic map?
• Pattern of magnetism over earth's surface
could be used in principle
• Wiltschko and Wiltschko (1996) showed
this would require minute discrimination:
0.03%. Daily variations are of same order.
• It is not clear how the map would work:
Angle of dip; Boles & Lohmann (2003)
lobsters
Home direction from odours
Wallraff (1967) reared pigeons in screened lofts:
• Those which could see the sun but not feel the wind got
lost
• Those which felt the wind but never saw the sun were
fine
• Odour hypothesis
From 1972 Papi and colleagues did many experiments
on anosmic pigeons
• There is a debate in the Navigation symposium. See
Wallraff (1996); Wiltschko (1996) and Able (1996)
• Odetti et al (2003) effects of flight experience on
orientation performance
Calibrating the systems
• Birds are not born with a star map
• Magnetic compass (angle of dip) reverses at the equator,
so needs to be recalibrated
• Savannah sparrows are born with a response to
magnetic field
• Helbig (1996) Genetics of response
• Migratory song birds also respond to celestial rotation
• Celestial compass updates the magnetic one during
migration
• But Sandberg et al (2000), 4 species calibrate star map
with magnetic cues.
Redundancy and balance between
systems
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Keeton: sun or magnets
Multiple systems
How much weight does a bird put on each
Learning two cues could mean less weight
to each
• Individuals may differ, based on their
experience. That would make
experiments hard to interpret