How do Birds Find Their Way? What we learned in the last 20 years

Introduction ► Given the power of flight, birds are highly mobile. ► Some species migrate and travel great distances.  Arctic Tern - 12,000 mile journey.  Manx Shearwater – Boston to Wales

Previous Studies ► Matthew’s Sun-Arc Theory  Birds look at the movement of the sun and compares angles and the noon azimuth to extrapolate latitude and longitude coordinates. ► Kramer’s Map and Compass Hypothesis  Birds establish a “Map” (direction to the goal) with the help of an external reference, a compass.

Current Studies ► Landmarks ► Stars ► Ultraviolet Light ► Infrasounds ► Sun ► Magnetic Fields ► Olfaction

Landmarks ► Pigeons tested using frosted contact lenses. ► There is some indication that birds use landmarks, at least sometimes. ► Not effective at night.

Stars ► Many birds migrate at night. ► “Cluster N” – Mouritsen et al ► Indigo Buntings seem to use the northern sky within about 35 degrees of the north star. ► Problematic in cloudy conditions and in Southern hemisphere.

Ultraviolet Light ► Study by Parrish et al. demonstrated birds can detect ultraviolet light. ► Effective even during cloudy days. ► Not readily studied.

Infrasounds ► Low Frequency Sounds (<10 Hz) ► Generated by wind, ocean waves, storms, mechanical devices, etc. ► Conditioned Cardiac Response  Pigeons hear less than 2 Hz. ► Not readily studied

Sun ► Sun acts as a compass (angles of light/shadow) ► Birds possess internal circadian clock. ► On cloudy days, Blue-winged Teal would circle until they got above the clouds at which time they started to move in the appropriate direction.

Magnetic Field ► Birds have magnetodetection senses (Mouritsen and Ritz 2005).  Birds have magnetite near the beak.  Cryptochromes in the eyes. ► Exact mechanism still unclear. ► Possible problems

Smells ► Intact sense of smell is necessary for goal- oriented homing of pigeons. ► Olfactory-based mechanism linked to piriform cortex. ► Trace gases/ratio of hydrocarbons at the home site distributed via winds may serve as a navigational cue (Wallraff 2005)

Which one(s) do they actually use? ► Most early studies on navigation tried to explain it by one mechanism. ► Orientation and navigation may be due to a variety of cues ► Path determined primarily by the sun. The magnetic field assists as a guide (Wikelski et al. 2004)

Does this apply to all birds? ► Wikelski seems to think so.  “It's such a simple and elegant mechanism that I would say it is widespread.” ► Species vary in their navigational ability.  i.e. Pigeons. ► Studies largely consist of a few species and are lab oriented.

Conclusion ► Despite all the theories and experiments dealing with navigation, there is much that is still not understood about how birds determine their position in relation to a fixed goal.

Future Research ► Is the sun used to calibrate the magnetic compass? – Cochran et al ► Extend analyses beyond homing pigeons and laboratory analyses. ► See how findings compare with other species (Salmon, Turtles, Sharks, etc).

Questions?