Migration 2

Question 1

How was the use of star compass demonstrated in birds?

Answer 1

-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

Question 2

What is inherited by birds?

Answer 2

Birds inherit the ability to use stellar compass

Question 3

What do birds learn during sensitive period?

Answer 3

Learn patterns of stars in the period between leaving the nest and starting the autumn migration

Question 4

How is the use of star compass learnt in Indigo buntings?

Answer 4

-Young birds learn to recognise constellations that move the least
-They do not need to see movement, they use constellations

Question 5

Indigo buntings reared in planetaria

Answer 5

-with normal sky (stars rotate around Polaris in north
– with false sky (stars rotate around Betelgeuse in south)

Question 6

What direction do Indigo buntings take when ready to migrate?

Answer 6

-they oriented south (as normal)
-oriented north (betelgeuse-trained)

Question 7

Explain the exp. carried out by Wiltschko

Answer 7

Placed Helmholtz coils around caged robins
- changed magnetic field altered robins’ sense of direction

Question 8

How are pigeons affected by the Helmholtz coil?

Answer 8

Pigeons showed that they use a magnetic compass in homing, but only if the sun is not visible

Question 9

What are the cues from the earth’s magnetic field?

Answer 9

-Polarity (direction of arrows)
-Inclination (parallel/perpendicular to earth surface)
-Intensity of field (longer lines, more intense

Question 10

What do birds use as compass?

Answer 10

Inclination

Question 11

What 2 coordinates are required for map location?

Answer 11

Latitude (easy)
Longitude (difficult)

Question 12

What forces vary with latitude?

Answer 12

Inclination and intensity

Question 13

Types of longitude

Answer 13

-Intersection of inclination and intensity isolines
-Inclination or intensity and other features

Question 14

What is declination?

Answer 14

The angular difference between magnetic and geographic pole

Question 15

Where are the two magnetoreceptors found in birds?

Answer 15

• Beak region: receptor based on magnetite crystals
  -In the eye: photochemical system

Question 16

How do photo-chemical compasses work in birds?

Answer 16

-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

Question 17

What do early experiments of odour and homing in birds show?

Answer 17

-Pigeons that could not smell were poor at homing
-Criticised: interventions (plugging, anaesthesia, cutting
nerve) may have reduced homing motivation

Question 18

What do later experiments of odour and homing in birds show?

Answer 18

-Wind deflected at loft, pigeon homing direction deflected
by similar amount
-Criticised: perhaps baffles also deflect sunlight, affect
sun compass

Question 19

How do pigeons use an odour map to navigate?

Answer 19

-Learn odours at home
-Use odour bouquet and wind direction to locate home
when displaced

Question 20

What are the mechanisms of long-distance orientation in birds?

Answer 20

1. Orientation by landmarks
2. Sun compass
3. Polarised light
4. Star compass
5. Magnetic compass-and map
6. Odour
7. Combination of factors (with hierarchy)

Question 21

What mechanisms are used by young pigeons?

Answer 21

-magnetic compass (exclusively on 1st flight)
-learn to use other cues (sun compass by 3month)

Question 22

What mechanisms are used by older pigeons?

Answer 22

-sun compass with magnetic compass as backup/influence
-landmarks
-odours