School › Animal migration › Ages 10–11
Why and how animals migrate
What triggers migration, how animals get ready, record-breaking journeys of butterflies, terns and whales, and the clues animals use to find the way. Then measure a migration on a globe and work out how long it takes.
Read
Migration is a regular, large-scale movement of animals. In North America alone, more than 300 kinds of bird are long-distance migrants.[1]
Birds that nest in the north fly there in spring to use a few months of plentiful insects and plants, lots of nesting space and long summer days for raising their young. Escaping the cold is not the main reason: many birds can survive freezing weather if they have enough food.[1][3]
The main signal to leave is the change in day length. Before the journey, birds store energy as fat: a small songbird can be up to half fat just before its first big flight.[1][3]
Monarch butterflies fly up to 3,000 miles (about 4,800 km), at about 50 to 100 miles (80 to 160 km) a day, to mountain forests in Mexico. The butterflies that fly south make the whole trip, but it takes three or four generations to get back to Canada.[4]
Arctic terns fly from the Arctic to the Antarctic and back: more than 50,000 km a year. Some humpback whales swim about 5,000 miles (about 8,000 km) between cold feeding seas and warm seas where calves are born.[1][9][5]
Animals use several clues to find the way: the sun, the stars, the Earth's magnetic field, landmarks such as rivers and mountains, and smell. Salmon use the magnetic field at sea, then smell to find the exact stream where they hatched.[2][6]
Try it: Measure a migration
You need
- A globe (or a world map with a scale bar)
- String or a strip of paper
- Ruler
- Calculator
- Sticky notes
Safety
Handle the globe carefully and keep it on a table. No special risks.
What to do
- Find southern Canada and the mountains west of Mexico City on the globe. Mark both with a sticky note.
- Lay the string along the shortest path between them on the globe. Mark the length on the string.
- Measure the string with the ruler and use the globe's scale to turn it into kilometres.
- Monarchs fly about 80 to 160 km a day. Work out the fewest and the most days the trip would take.
- Repeat for a swallow flying from your country to South Africa, and for an Arctic tern from Greenland to Antarctica.
- Compare your answers with other groups. Why are they not all the same?
What happens, and why?
A butterfly does not fly in a straight line, and it flies further on some days than others, so your answer is an estimate. The Forest Service says the monarch's trip of up to 3,000 miles (about 4,800 km) can take up to two months, flying 50 to 100 miles a day.[4]
Play: Which clue?
Each animal or experiment uses a clue to find the way. Is it the sky, the Earth's magnetic field, or landmarks and smell?
Your best score is kept only on this device. Nothing is sent anywhere.
Quiz
Other ages: Ages 6–7 · Ages 15–16