Navigation Flashcards
Why do animals need spacial skills?
1) Getting home after displacement
2) Finding something you left behind = target finding
3) Dispersal and migration
What methods are used to navigate?
- Simple rules to stay in environment
- Dead reckoning
- Piloting using map and compass
Give an example of how simple Rules can be used by animals to stay in environment
Woodlice wish to return to a type of habitat – wet and dark. Very simple rule allows this:
Rule : Turn much more in nice habitat
Result : Stay there much longer
What is dead reckoning in navigation?
- process of calculating one’s current position by using a previously determined position, or fix, and advancing that position based upon known or estimated speeds over elapsed time and course.
Give an example of dead reckoning in navigation?
Desert ant
- Goes on wiggly route out, looking for food.
- Straight line back to nest with the food.
- Works out direction by “Route integration”, i.e. adds all the runs and turns, and calculates direction home.
Describe how animals can pilot by Landmarks
Beewolves (Tinbergen)
Beewolf wasp feeds her grubs paralysed bees in underground burrow among hundreds of others on dune. How does she find it?
Experiment -
put cones round burrow while wasp inside.
Wasp did orientation flight to learn new landmarks.
While she was away, Niko moved the cones.
Wasp searched repeatedly in centre of cones.
Conclusion: must use landmarks to recognise burrow position.
How do the beewolves use landmarks to navigate?
Beewolf forms a mental map of the landmarks
Must be able to adjust map though, when landmarks change.
Beewolf appears to do this on orientation flight when leaving the nest.
More complex in honeybees as many more images remembered.
What animals use landmarks for piloting?
Beewolves
Honey Bee’s
Mice
Food Storing Birds
What different maps are used to navigate?
- Landmark maps
- Current maps
- Sound maps
- Olfactory maps
Describe how animals use current maps to navigate
green turtles
- All born on beaches of Ascention Island
- Drift in current to eel grass beds in Brazil. (Evidence of magnetic sense acting too)
- return when adult to same beach by swimming up the current until close to the island.
- Unknown how they find their original beach though. - probs olfactory map of island
Describe how animals use sound maps to navigate
pigeons and whales use infrasound maps
Sources = breaking waves, wind over mountains etc. make very low frequency sounds called infrasound.
Infrasound travels a very long way with little attenuation so good for maps.
Describe how animals use olfactory maps to navigate
pigeons, shearwaters, eels, salmon
All return to natal river or nest site across apparently featureless sea.
Appear to use local smells as a map for navigation.
How do animals use directional information from celestial cues as compasses for navigation
- position of sunset can give the direction of west, without using an internal clock
- all night as you travel so inaccurate if used alone.
- The north star is the only star that doesn’t move through the night, so also tells you where north is without the need for a sense of time.
- most celestial bodies (sun, moon, or stars), move with time of day, making it difficult to use them as a compass.
- animal must have a clock of some sort to interpret the position of the celestial body, to give direction.
How do we demonstrate that some animals have a clock of some sort to interpret the position of the celestial body, to give direction?
Clock shift experiments
- Keep bird in room with no windows
- Expose it for several days to lights turned on at noon and off at midnight instead of sunrise at 6am and dusk at 6pm
- This confuses its internal clock into thinking it is 6am (dawn) when really it is noon
- When bird is let out at noon, its internal clock thinks it is 6am, and that the sun is just rising in the east. In fact the sun is in the south at noon.
-So the bird, who wants to go south west, flies off in the wrong direction.
Good evidence that direction was assessed by bird using a combination of sun position and internal clock.
Are birds using the sun and clock compass?
- starlings kept in a round loft surrounded by windows
- All orientated in same direction if can see the sun, but at random if sky overcast.
- Put mirrors by windows so reflected light at 90o to sun
- Birds orientated to new “sun position”
Conclusion: birds were using the sun to tell them compass direction
Must be using a clock to interpret the sun’s position too
Is a sense of direction enough to get you home?
Knowing which way is North doesn’t tell you where you are or where your home is. You need a map.
- Having a map is no good unless you know which way you are facing, so need a compass (and probably therefore a clock)
- You also need to know where on the map you are, and where your target is.
- Long distance navigation such as migration may have to be very sophisticated!
What is an emlen funnel?
bird cage shaped like an inverted cone, used to study bird behaviour, in particular birds’ migratory instincts
- Bird stands on ink pad and marks the walls of the funnel as it flutters up.
- After an hour or so, it is clear which direction the bird wants to fly.
What is Zugunruhe?
(Zug = travel; unruhe = unrest)
birds in lab showed directional restlessness when their conspecifics were migrating.
Gwinner and Wiltschko 1978 worked on Garden Warblers and measured their zugunruhe using an Emlen funnel. Why did they choose garden warblers?
Chose garden warblers because they have a turn in their migration path.
Gwinner and Wiltschko 1978 worked on Garden Warblers and measured their zugunruhe using an Emlen funnel
- Measured the activity of captive warblers during the whole time their conspecifics were migrating
- Showed they changed direction of zugunruhe when conspecifics turned.
- Conclusion: migrate by timing of activity in each direction, not appreciation of their actual position – very simple rules for travel!
In what animals is the magnetic sense present in?
birds, insects, amphibians, molluscs, fish, … & humans?
How do animals have the magnetic sense?
Magnetite – sensory organs (nasal region)
Have magnetite in sense organs, in nasal region, ear and possibly in eye. Might even give the equivalent of an image of the magnetic field.
What is the purpose of magnetic sense?
May give information on direction AND latitude on Earth’s surface (not longitude though) at least to homing pigeons.
Not much known but seems to sense dip of magnet towards centre of earth, not direction of poles.
In addition maybe can build up map of local fluctuations in magnetic field.
Do humans have magnetic sense?
Humans “are not believed to have a magnetic sense”, but humans do have a cryptochrome (a flavoprotein, CRY2) in the retina which has a light-dependent magnetosensitivity. CRY2 “has the molecular capability to function as a light-sensitive magnetosensor”, so the area was thought (2011) to be ripe for further study
Describe an experiment that proved magnetic sense in pigeons
- Chose an overcast day so couldn’t use sun.
- Attached Helmholtz coil to pigeons’ heads, which locally reversed magnetic field round the birds’ heads.
- Turn on with half the birds, off as a control in the other birds
- Allowed pigeons to home.
- Result: Those with the coils turned off made it home quickly.
Those with it turned on flew in opposite direction. - Conclusion: Pigeons were using the earth’s magnetic field to help them get home.
What is a helmholtz coil?
a device for producing a region of nearly uniform magnetic field. It consists of two electromagnets on the same axis
Name different cues used for navigation
Landmarks Celestial Compass & Clock Polarised Light Point of Sunset Magnetic Sense Cognitive Maps
Do animals rely on one cue for navigation?
- Used in combination, few animals rely on just one.
- Most have a preference for which one they use first, but will use 2nd favourite when first isn’t available.
What is “True” Navigation?
knowing where you are without knowing how you got there, i.e. innate sense of where you are on the map
Give an example of what might be true navigation
- Monarch Butterfly - Migrates to Mexico to traditional overwintering sites where thousands gather.
- In spring flies north, lays eggs and dies.
- Offspring fly further north, and die
- 3 generations later Winter comes.
- Monarch of that generation flies back to exactly the same site his great grandfather left.
Sun rises to the ___________ and sets to the _____________.
east, west
Monarch butterflies migrate to…
Mexico
Why do birds migrate?
Food, climate compatibility, nesting locations
Built-in clock that birds have that help them determine the time of day and change in day length.
circa-annual clock
True or False: Birds ALWAYS migrate with a tailwind.
True.
Tailwind - a wind blowing in the direction of travel
Contraption used to determine whether birds can orient themselves in the absence of stars. It uses a funnel coated in blotting paper and entails the bird resting at the bottom in an ink pad and then analyzing the concentration of footprints about the funnel to determine a direction.
Emlen Funnel
3 compass systems of migrating birds
Sun, stars, Earth’s magnetic field
Mechanisms of Organization for Bird Navigation
Piloting: Going by familiar landmarks
Compassing: Knowing the directions and navigating accordingly
Mapping: Knowing where you want to go in relation to where you are
True or False: Pigeons rely on distinct landmarks to navigate.
False
What are the 2 directional tools of a homing pigeon?
Compass and map
How could you test the influence of sunlight upon homing pigeons’ abilities to orient themselves?
Clock shift. Keep them in a closed setting where you can manipulate the light exposure and shift the daylight hours backwards or forwards.
True or False: Birds are opportunists. They utilize whatever cues they have available to find their way home.
True
True or False: Pigeons use wind as a directional cue
False
True or False: Animals do not have flexibility in determining the environmental cues they will utilize in their navigation.
False
