Define navigation
Ability to move from current location to an alternative location. Requires knowledge of current location in space, as well as desired location.
Define orientation
The ability to know which compass (magnetic) direction the individual is facing. Requires an internal representation of the different directions.
Examples of migratory species:
Humpback whales - move from Russia/Alaska (summer feeding) to Hawaii (winter breeding).
Salmon - return to the location where they were raised to breed.
What cues to homing pigeons use to navigate?
- Olfactory cues (gradient)
- Landmarks, e.g. roads, buildings.
- Geomagnetic gradient (magnetoreceptor?)
- Sun and stars in sky
Describe Emlen’s funnel
- Funnel with filter paper on sloped sides.
- Ink pad on the bottom of the funnel.
- Bird inside will jump from the bottom onto the sides on the funnel.
- No visual cues given, e.g. light.
- The ink markings will track the location of landings.
- The ink markings are significantly grouped in the direction of the natural migratory route of the species
- -> North in summer, south in winter.
Who proposed that birds orient selves in the direction of migration?
Merkel, Fromme and Wiltschko - European Robin
Name for movement in anticipation more mass movement of individuals.
Pre migratory restlessness.
What happens if manipulate direction of sunlight exposed to migratory birds? What does this suggest?
Birds will change the direction of their pre-migratory restlessness movements. Suggests that these movements are based on the direction of the sun.
What geomagnetic cues can birds use?
Compass needle will point downwards if in Northern hemisphere, and upwards if in southern hemisphere.
This could be used as clue for latitude? Magnetoreceptor
What cues do birds use to navigate at night?
- Use compass cues to set direction at twilight (primary cue).
- Then use other locational cues to sustain the correct direction in absence of light.
- Will recalibrate on the following night to check that they are on the right track.
- Can use stars - aware that the north star is stationary, and all other stars move around it.
- use solar azimuth (angle of sun) at sunrise and sunset.
- -> Find west/east.
- May explain how some birds can fly over the equator without becoming disorientated.
What are ferromagnetic substances?
Attracted strongly by magnetic field. e.g. Iron, cobalt and nickel.
What is magnetite?
Iodestone - Fe3O4.
When cut into small pieces, will align with the mag fields of the earth.
Discuss the theories of the magnetite receptors in animals.
- Evidence of magnetite in teeth of molluscs.
- Suggested that there is a magnetite receptor in beaks of birds - part of trigeminal nerve?
- Suggested in right eye - if R eye is covered, European robin is unable to orient self. BUT - is this using binocular vision? depth perception?
- Magnetite found in macrophages - does it have a role in navigation?
- Wu and Dickman - suggest that there is an ion channel receptor which is controlled via changes in electromagnetism. –> opens the channel mechanically when due to attraction of magnetite in certain polarities.
- Mouritsen - suggests there is magnetite receptor in eye of European robin. Light sensitive, and based on chryptochrone proteins (sensitive to blue light, involved in circadian rhythms).
Effect of olfactory system lesions in homing pigeons.
Effect of filtered air.
Reduces ability to return to original location
Suggests that they use olfaction as a primary sense in directions.
As distance of release increases from origin, the success of lesioned birds decreases.
If air is filtered, unable to use the olfactory cues. Success decreases.
What physical cues to birds use?
Landmarks:
- roads - size of road important, will have preference for larger less direct roads.
- use junctions
- understand permanence of these structures, and they are useful cues in distance travelled. May help to determine their altitude? could be cue of how high they are flying? Or they use their knowledge of their altitude to determine the distance travelled using landmarks as reference points.
- may use roads and traffic nodes as landmarks.
- can increase certainty that they are travelling in the correct direction.
- following a road may require a lower cognitive load - increase available neural capacity.
- could use the innate compass to determine direction, and then use the landmarks to determine if continuing in the desired location?
Can birds accommodate for displacement?
If birds have previous flight experience, will compensate for displacement.
If do not have previous flight experience, they will not compensate for displacement.
Young birds will follow older birds - use prior knowledge of routes.
This could be a form of culture? passed from one generation to another?
What are the reasons for migration?
- Will track the availability of biomass for consumption.
- More common in birds that are unable to adapt to the changing environment.
- more common in birds with less feeding and breeding innovation.
- innovation can include the use of tools for digging etc.
- could this be a reason for why humans do not migrate?
We are able to manipulate the environment, through learning and culture. So we have lost the ability to navigate effectively? or the loss of navigation prompted the increasing in cultural transmission? CAUSE OR EFFECT? - Resident birds often have sig larger brain.
What effects do humans have on migratory behaviour?
White Stork:
- Usually migrate from Poland to Africa.
- Increased availability in food closer to breeding ground prevents birds from making full journey, therefore will stop on the way.
- will have knock-on impact on the ecosystems that they should be going to/are now staying it –> unbalanced, and unstable.
