Read

Migration is triggered mainly by changing day length, along with temperature and food; hormone changes make caged birds restless and face the direction they would migrate (Zugunruhe). Most birds migrate at night.

Fat is the most energy-dense fuel: it gives more than twice the energy of carbohydrate or protein per gram. Small songbirds can be up to 50% fat before their first big flight, and a godwit's mass can more than double.

In 2007 a bar-tailed godwit called E7 flew about 7,250 miles (about 11,700 km) nonstop from Alaska to New Zealand in about 8 days, averaging nearly 35 miles per hour (about 56 km/h) without food or water. A 2005 study had already argued for an 11,000 km nonstop flight from re-sightings of marked birds, fat loads and flight models.

Experiment: Mapping a magnetic field: what a magnetic compass can and cannot tell

1. Put the bar magnet in the middle of the paper and draw round it. Keep other magnets and steel objects away.
2. Place a plotting compass near the north pole and mark the point its needle points to. Move the compass to that point and repeat, building up a field line from pole to pole. Draw at least six field lines.
3. Mark the direction of the field with arrows. Then turn the magnet round (swap the poles) and check how the arrows change.
4. Discuss: if an animal could sense only the line (axis) of the field and how steeply it dips, but not which end is north, what could it still work out? (Hint: compare the steepness of field lines near the poles of the magnet and at its middle.)
5. Optional: use a dip needle or a magnetometer app to measure the angle of the Earth's field to the horizontal in your classroom.
6. Evaluate: list sources of error (nearby steel, the compass's own size, reading the needle angle).

Position	Field direction (sketch)	Angle to the magnet's axis (°)
Near N pole
Near S pole
Middle, above the magnet
Far from the magnet

Questions

1. E7 flew about 11,700 km in about 8 days. Calculate its average speed in km/h and compare it with the reported 56 km/h. Suggest why they differ.

2. Explain why migrating birds store fat, and give one figure from the text.

3. Describe one experiment that tested a bird compass: what was changed, what was observed, and what it showed.

4. From your field map, explain what an animal that senses only the axis and dip of the field could and could not tell.

Sources for every fact on this sheet: echoesof.science/school/migration/sources/

🖨 Print this sheet ← back to the lesson