Migration 2 Flashcards
How was the use of star compass demonstrated in birds?
-Experiments with caged warblers (nocturnal migrants) showed lack of orientation indoors, but directed movement (north in spring, south in autumn) when allowed see the night sky.
-confirmed by Emlen using caged indigo bluntings
What is inherited by birds?
Birds inherit the ability to use stellar compass
What do birds learn during sensitive period?
Learn patterns of stars in the period between leaving the nest and starting the autumn migration
How is the use of star compass learnt in Indigo buntings?
-Young birds learn to recognise constellations that move the least
-They do not need to see movement, they use constellations
Indigo buntings reared in planetaria
-with normal sky (stars rotate around Polaris in north
– with false sky (stars rotate around Betelgeuse in south)
What direction do Indigo buntings take when ready to migrate?
-they oriented south (as normal)
-oriented north (betelgeuse-trained)
Explain the exp. carried out by Wiltschko
Placed Helmholtz coils around caged robins
- changed magnetic field altered robins’ sense of direction
How are pigeons affected by the Helmholtz coil?
Pigeons showed that they use a magnetic compass in homing, but only if the sun is not visible
What are the cues from the earth’s magnetic field?
-Polarity (direction of arrows)
-Inclination (parallel/perpendicular to earth surface)
-Intensity of field (longer lines, more intense
What do birds use as compass?
Inclination
What 2 coordinates are required for map location?
Latitude (easy)
Longitude (difficult)
What forces vary with latitude?
Inclination and intensity
Types of longitude
-Intersection of inclination and intensity isolines
-Inclination or intensity and other features
What is declination?
The angular difference between magnetic and geographic pole
Where are the two magnetoreceptors found in birds?
- Beak region: receptor based on magnetite crystals
-In the eye: photochemical system
How do photo-chemical compasses work in birds?
-photoreceptors in bird’s retina absorb light;
- electron transfer produces radical pairs that can exist in 2
states
- Interconversion between the states is influenced by a weak
magnetic field
What do early experiments of odour and homing in birds show?
-Pigeons that could not smell were poor at homing
-Criticised: interventions (plugging, anaesthesia, cutting
nerve) may have reduced homing motivation
What do later experiments of odour and homing in birds show?
-Wind deflected at loft, pigeon homing direction deflected
by similar amount
-Criticised: perhaps baffles also deflect sunlight, affect
sun compass
How do pigeons use an odour map to navigate?
-Learn odours at home
-Use odour bouquet and wind direction to locate home
when displaced
What are the mechanisms of long-distance orientation in birds?
- Orientation by landmarks
- Sun compass
- Polarised light
- Star compass
- Magnetic compass-and map
- Odour
- Combination of factors (with hierarchy)
What mechanisms are used by young pigeons?
-magnetic compass (exclusively on 1st flight)
-learn to use other cues (sun compass by 3month)
What mechanisms are used by older pigeons?
-sun compass with magnetic compass as backup/influence
-landmarks
-odours
