Grades 6–8 · Organisms
How can a monarch use the moving Sun as a compass?
A migrating monarch can keep a broadly consistent direction even while the Sun changes position across the sky. Simply keeping the Sun at one fixed angle to its body would not do this: as the light direction changed, that simple rule would turn the butterfly’s course.
In the diagramA moving Sun needs a time correctionLater▸ Daily clockTimingNSEWSunClock + lightTime correctionSelected heading keptA biological clock supplies daily timing.
Eastern North American monarchs migrating in autumn use a time-compensated sun compass. The eyes obtain directional information from sunlight and the sky. An internal circadian clock, a biological rhythm that runs on a roughly daily cycle, supplies information about time. Light helps keep that timing aligned with the day.
The nervous system combines directional and timing information. The useful relationship between the Sun and a chosen compass heading changes through the day, so the butterfly needs a changing correction rather than one unchanging angle. Experiments that shift the animals’ light-and-dark schedule also shift their flight orientation, supporting the clock’s role.
Research identifies clocks in the antennae as important timing components. This does not mean that the antennae alone contain a complete map or that one compass explains every part of migration. The illustration uses invented Sun positions to show why a time correction matters, not to reproduce an actual route or measured flight bearing.
About this explanation
Starting knowledge: Understands compass directions, daily changes in the Sun’s apparent position and biological signals.
Sources
- Merlin, Gegear and Reppert, Science — Antennal circadian clocks coordinate sun compass orientation in migratory monarch butterflies
- University of Massachusetts Chan Medical School, Reppert Laboratory — The Circadian Clock: Antennal Clocks
- University of Massachusetts Chan Medical School, Reppert Laboratory — Clock-Compass Interactions