L4 Migration patterns & biological compasses

Partial

Only part of the population is migratory

Differential

migration where distance traveled differs between portions of a population

Nomadic

migration does not follow a regular pattern or route but links temporary breeding sites that are located where conditions are ephemerally favorable

• Ex. leatherbacks, caribou

Irruptive

occasional, irregular movements of a significant proportion of a population beyond its usual breeding or nonbreeding area

• Ex. crossbills, insects like locusts

Diadromic

Moving between salt and freshwater

Altitudinal

Migration up/down mountains

Cultural transmission

More flexible than a genetically encoded route, but require parents to go with offspring

Leap-frog

individuals from northern parts of the breeding range are forced by intraspecific competition to continue to wintering grounds further south

Chain migration

latitudinal segregation during the breeding season is maintained during wintering

Paralell migration

longitudinal segregation is maintained throughout the year

Orientation

the ability to define a compass direction

Navigation

the ability to define your position relative to a distant goal

Sun compass

• Time compensation needed

• Experience needed

• Rotation center

• Skylight polarization pattern to detect sun azimuth on cloudy days

• Good for:

  • Great circle routes (ex. waders in arctic)

• Compass set at departure, not recalibrated during flight

Skylight polarization

• Symmetrical to the position of the sun

• E-vector pattern

• Solar meridian

• Provides directions relative to geographic north

• Compass information

Stellar compass

• No time compensation

• Rotation center

• Experience needed

• Star patterns can be learned

Geomagnetic compass

• Detecting angle of inclination, not polarity

• Inclination relative to N-S axis provides information on pole-ward and euqtor-ward directions

• Inherited

• Population and species specific direction

• Inclination compass

• Photoreceptor-based detection

• Radical pair process