Bird Navigation Flashcards
Why is it only in the last 10-12 years that bird navigation research has really taken off
GPS location devices have allowed researchers to track where birds migrate
What do we mean by ‘orientation’
The ability to identify compass directions. Orientation implies an ability to acquire an internal representation of compass directions
What do we mean by ‘navigation’
The ability to identify current position and move to a new location. Implies knowledge of where you are and where you want to go
Give an example of a large migratory route
The bobolink flies up to 7000 km every autumn from Canada/US (where it summers) to Bolivia/Argentina/Brazil (where it winters)
Why are pigeons useful in the study of navigation
Because pigeons home -they will fly back to their home loft in which they were raised. Can study the type of cues these birds use to navigate back to the home loft.
What are some of the proposed cues that birds use to navigate
Sun compass (position of the sun) Chemical gradient (may be a particular signature of wind-bourne chemicals near the home loft which the bird can use to navigate back to the home loft by flying across the chemical gradient using olfaction) Visual landmarks Magnetic gradient (initially learn about the magnetic field of the home loft and use that to navigate back)
What are some of the difficulties faced when studying bird navigation
You can try and manipulate one cue at a time to pinpoint its contribution, but you may not detect a difference because the bird is likely to use multiple cues when navigating so can switch strategies.
In the lab you can manipulate individual cues, but you are also relying on the animal to exhibit its natural behavioural traits - it is unlikely to do this in the lab
Who first suggested that birds possess a magnetic compass
Alexander Theodor Von Middendorf (1850s)
Which group of scientists made a major breakthrough in migration research? When was this
Friedrich Merkel and colleagues. 1958 - 1965
Who investigated premigratory restlessness in the European Robin
Merkel, Fromme and Wiltschko
What is premigratory restlessness
The unsettled behaviour of birds before they are due to depart on migration
What did Merkel, Fromme and Wiltschko discover about premigratory restlessness. Describe how they found this
In lab conditions, they discovered that there was a variation in preferred orientation of movement depending on the time of year (spring or autumn).
They used Emlen’s funnel to measure primigratory restlessness.
Funnel-shaped device with white filter paper around the inside. Ink pad at the bottom which the bird stands on. The ink transfers to the birds feet and you can then visualise where the bird jumps on the funnel.
Looked at where most of the birds jumping movements were oriented.
In autumn, most movement was in a southerly direction
In spring, most movement was in a northerly direction
Birds show this even in a room without external visual cues.
Must mean that the bird is able to sense compass directions.
If you remove local magnetic field information you can disrupt premigratory restlessness.
What happens when you manipulate the direction that the sun is entering Emlen’s funnel. What does this show
You can change the orientation of the bird’s premigratory restlessness. Shows that birds use position of the sun as a cue as well and can compensate for the sun’s position in the sky
What study demonstrated that night-time migrants may use the position of the stars to navigate
Study where indigo buntings were raised in a mini planetarium.
Manipulated the rotation of the night sky (i.e. which star the stars seem to rotate around).
Birds orient to the stellar cues they are exposed to - change their orientation to the change in rotation of the night sky
How did Cochran et al. (2004) show that birds use geomagnetic cues as well as twilight cues
Studied two species of thrush (grey cheeked thrush and swainskn thrush).
These are nocturnal migrants - leave at twilight, stop some time in early morning.
Before the birds left for the first flight they manipulated the local magnetic field.
They attached a little antenna to the birds and traced the signal with an Ariel attached to the car.
For the birds that were subject to the manipulated magnetic field, they flew off in the wrong direction.
Suggests that the birds use local magnetic cues to calibrate the flight.
The next day these birds were not subject to magnetic field manipulation.
They changed the direction of their flight to compensate for the previous deviation.
Suggests that these birds integrate twilight cues with local magnetic sense to determine the direction of their flight.
What do the findings from Cochran et al (2004) suggest birds posses?
A geomagnetic receptor
What two geomagnetic cues could birds use?
Polarity and inclination
What is polarity?
The direction of the magnetic field. The northern hemisphere points towards magnetic north and the Southern Hemisphere points towards magnetic south.
What information does polarity give you
Whether you are in the northern or Southern Hemisphere
What information does inclination give you
Where you are in the northern or southern hemisphere
Which geomagnetic cue do birds use most?
Inclination
What are ferromagnetic compounds? Give examples of these
Naturally occurring compounds in the environment which are strongly attracted by magnetic fields. Iron, cobalt, Nickel
What is magnetite
An oxide of iron and a natural magnet
What makes magnetite a likely candidate to be involved in the geomagnetic receptor
Magnetite can be cut into very small threads that align with the earth’s magnetic field, including the angle of the magnetic field (so responsive to polarity and inclination)
Give examples where magnetite exists within animals
Mollusc teeth are coated in magnetite
Sockeye salmon has magnetite in tissues in the frontal region
How might a magnetite receptor function
String of magnetite crystals attached to a stretch receptor. Stretch receptors activated by movement of magnetic crystals - triggers influx of certain ions which alter activity of neuron
What behavioural test provides modest evidence that pigeons can detect magnetic fields
Place pigeon in behavioural testing apparatus, where the magnetic field can be manipulated.
Either side of box there is a light and a food hopper
Train pigeon to associate the polarity of the magnetic field with the respective food hopper.
Modest evidence that the pigeon can detect this change in magnetic field and learn to use it.
Where have researchers suggested this magnetic receptor may be in birds?
The beak
The right eye
The inner ear
What evidence is there to suggest that the magnetic receptor is in the beak?
Fleissner et al. (2003) - anatomical evidence of magnetite in pigeon beak
Hypothesis = magnoreceptor may exist within the hypothalamic branch of the trigeminal nerve - change in the magnetic field signalled by the trigeminal system.
Cardion and McNaughton (2010) - electrophysiological recordings from the trigeminal nucleus.
Demonstrated changes in activity of the trigeminal nucleus with changes in the strength of the magnetic field.
So able to code strength of magnetic field?
What evidence is there to suggest that the magnetic receptor is in the right eye?
Captive European robins can orient using only geomagnetic cues, but not when the right eye is covered.
Indicates that this sense is localised within the right eye.
But Mouritsen - suggests the magnoreceptor within the European robin eye is light-dependant. Mechanism based on cryptochrome proteins.
What evidence is there to suggest that the magnetic receptor is in the inner ear?
Wu and Dickman (2011) - measured c-fos expression (marker of neuronal activity) in response to magnetic pulse.
Found increased c-fos expression in the vestibular nuclei.
This can be reduced by lesioning the inner ear, which removes the lagena.
The lagena provides the input to the vestibular nuclei so thought that magnoreceptor exists within the inner ear.
Wu and Dickman (2012) - electrophysiological recordings from the vestibular nuclei in pigeons.
Found cells in this region that were both responsive and unresponsive to magnetic stimulation.
Also found evidence that these cells could code the direction and intensity of the Earth’s magnetic field.
What evidence is there which shows that birds rely on olfactory cues for navigation
Pigeons with severed olfactory nerves show impairments in navigating back to the home loft.
Suggests that the sensation of chemicals associated with the home loft is important.
The navigation impairment is more apparent with distant release sites.
Raise pigeons in loft where the air is filtered (so remove olfactory cues).
Subtly impair the pigeons ability to navigate back to home loft.
What evidence is there which shows that birds use landmarks to navigate
Lipp et al. (2004) - able to use GPS to track pigeon homing behaviour.
Released birds at various sites and track their route back to the loft.
Birds learn with experience to use motorways and railways over more direct beeline route to navigate back to home loft.
Many routes converged at exit 22 on the motorway - birds seem to be using this landmark as a ‘beacon’ to determine where the loft is.
The more experienced the birds were with the landscape, the more they used the motorways and railways.
Appear to develop preference for road-following
Why would it be beneficial for birds to follow man-made landmarks?
To avoid the unknown - man-made landmarks are reliable so less likely to accumulate errors over journey.
By using landmarks over other cues like geomagnetism or olfactory cues, bird may free up cognitive resources.
Describe the study showed that birds may posses a cognitive map?
Used the white crowned sparrow (species of songbird which resides in the west coast of America and flies to california / Mexico in the autumn) - north-south migration.
Birds were displaced 3700 km east before they started migration and then released.
Adults were able to compensate for the displacement - migrate in the right direction.
Juvenile birds which had never undertaken the north-south migratory route did not compensate - just flew south.
Somehow experienced birds know they have been displaced - have they built up a ‘continental map’?
What did Mueller et al (2013) show about whooping cranes’ migratory behaviour?
The presence of older birds influences the migratory route (perhaps making it more efficient).
Idea is that the inexperienced birds learn the best route to take from the experienced birds over time.
Give two examples of palearctic resident birds and their innovation for finding food in the winter
Blackbird - can use twigs to clear away snow when looking for food
Bullfinch - eats flesh from chicken and duck carcasses
What could the evolution of migratory behaviour be linked to? Why is this?
Capacity for innovation.
Meta-analysis of migrant and non-migrant palearctic birds suggest that migrant species do not possess the same level of problem solving ability as non-migrant birds.
So in the winter when food is scarce migrant birds fly south in search of more abundant supplies of food.
Resident species show greater innovation and relative brain size.
