How do Birds Find How do Birds Find Their Way?Their Way?

What we learned in the last What we learned in the last 20 years20 years

IntroductionIntroduction

►Given the power of Given the power of flight, birds are flight, birds are highly mobile.highly mobile.

► Some species Some species migrate and travel migrate and travel great distances. great distances. Arctic Tern - 12,000 Arctic Tern - 12,000

mile journey.mile journey. Manx Shearwater – Manx Shearwater –

Boston to WalesBoston to Wales

Previous StudiesPrevious Studies

►Matthew’s Sun-Arc TheoryMatthew’s Sun-Arc Theory Birds look at the movement of Birds look at the movement of

the sun and compares angles the sun and compares angles and the noon azimuth to and the noon azimuth to extrapolate latitude and extrapolate latitude and longitude coordinates.longitude coordinates.

► Kramer’s Map and Compass Kramer’s Map and Compass HypothesisHypothesis Birds establish a “Map” Birds establish a “Map”

(direction to the goal) with (direction to the goal) with the help of an external the help of an external reference, a compass. reference, a compass.

Current StudiesCurrent Studies

► LandmarksLandmarks► StarsStars► Ultraviolet LightUltraviolet Light► InfrasoundsInfrasounds► SunSun►Magnetic FieldsMagnetic Fields►OlfactionOlfaction

LandmarksLandmarks

► Pigeons tested Pigeons tested using frosted using frosted contact lenses.contact lenses.

► There is some There is some indication that birds indication that birds use landmarks, at use landmarks, at least sometimes. least sometimes.

►Not effective at Not effective at night. night.

StarsStars

►Many birds migrate at Many birds migrate at night.night.

► ““Cluster N” – Mouritsen Cluster N” – Mouritsen et al. 2005et al. 2005

► Indigo Buntings seem to Indigo Buntings seem to use the northern sky use the northern sky within about 35 degrees within about 35 degrees of the north star.of the north star.

► Problematic in cloudy Problematic in cloudy conditions and in conditions and in Southern hemisphere.Southern hemisphere.

Ultraviolet LightUltraviolet Light

► Study by Parrish et Study by Parrish et al. demonstrated al. demonstrated birds can detect birds can detect ultraviolet light. ultraviolet light.

► Effective even Effective even during cloudy days.during cloudy days.

►Not readily studied.Not readily studied.

InfrasoundsInfrasounds

► Low Frequency Sounds Low Frequency Sounds (<10 Hz)(<10 Hz)

► Generated by wind, Generated by wind, ocean waves, storms, ocean waves, storms, mechanical devices, mechanical devices, etc.etc.

► Conditioned Cardiac Conditioned Cardiac ResponseResponse Pigeons hear less than 2 Pigeons hear less than 2

Hz.Hz.

► Not readily studiedNot readily studied

SunSun

► Sun acts as a compass (angles Sun acts as a compass (angles of light/shadow)of light/shadow)

► Birds possess internal circadian Birds possess internal circadian clock.clock.

► On cloudy days, Blue-winged On cloudy days, Blue-winged Teal would circle until they got Teal would circle until they got above the clouds at which time above the clouds at which time they started to move in the they started to move in the appropriate direction. appropriate direction.

Magnetic FieldMagnetic Field

► Birds have Birds have magnetodetection senses magnetodetection senses (Mouritsen and Ritz (Mouritsen and Ritz 2005).2005). Birds have magnetite near Birds have magnetite near

the beak.the beak. Cryptochromes in the eyes.Cryptochromes in the eyes.

► Exact mechanism still Exact mechanism still unclear.unclear.

► Possible problemsPossible problems

SmellsSmells

► Intact sense of smell is Intact sense of smell is necessary for goal-necessary for goal-oriented homing of oriented homing of pigeons.pigeons.

► Olfactory-based Olfactory-based mechanism linked to mechanism linked to piriform cortex.piriform cortex.

► Trace gases/ratio of Trace gases/ratio of hydrocarbons at the hydrocarbons at the home site distributed home site distributed via winds may serve as via winds may serve as a navigational cue a navigational cue (Wallraff 2005)(Wallraff 2005)

Which one(s) do they actually Which one(s) do they actually use?use?

►     Most early studies on navigation tried Most early studies on navigation tried to explain it by one mechanism. to explain it by one mechanism.

► Orientation and navigation may be Orientation and navigation may be due to a variety of cues due to a variety of cues

►Path determined primarily by the sun. Path determined primarily by the sun. The magnetic field assists as a guide The magnetic field assists as a guide (Wikelski et al. 2004)(Wikelski et al. 2004)

Does this apply to all birds?Does this apply to all birds?

► Wikelski seems to think Wikelski seems to think so.so. ““It's such a simple and It's such a simple and

elegant mechanism that I elegant mechanism that I would say it is would say it is widespread.”widespread.”

► Species vary in their Species vary in their navigational ability.navigational ability. i.e. Pigeons.i.e. Pigeons.

► Studies largely consist Studies largely consist of a few species and are of a few species and are lab oriented.lab oriented.

ConclusionConclusion

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

Future Research Future Research

► Is the sun used to calibrate the Is the sun used to calibrate the magnetic compass? – Cochran et al. magnetic compass? – Cochran et al. 20042004

►Extend analyses beyond homing Extend analyses beyond homing pigeons and laboratory analyses. pigeons and laboratory analyses.

►See how findings compare with other See how findings compare with other species (Salmon, Turtles, Sharks, etc).species (Salmon, Turtles, Sharks, etc).

Questions?Questions?