Slide 1
A migration exceeds one short life
Eastern North American monarchs complete their annual migration across generations. The northbound butterflies are not all the individuals that later return south.
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Survivors leave Mexican wintering areas in spring and reproduce along the northward route. Their descendants continue the seasonal expansion, connecting breeding across a large region.
Slide 2
The autumn generation differs
A late-season generation lives longer and delays reproduction while migrating. These butterflies can make the long southward journey to overwintering areas.
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Seasonal changes help trigger this state. The same species has different life-history schedules depending on when individuals develop, allowing a long journey that short-lived summer generations would not complete.
Slide 3
Milkweed supports the young
Monarch caterpillars depend on milkweed host plants. Adults need nectar from flowers to fuel their own activity and migration.
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A field rich in nectar may still lack larval food. Conservation must therefore connect resources for different life stages rather than treating all flowering vegetation as equivalent monarch habitat.
Slide 4
Winter is part of the route
Suitable overwintering habitat allows migratory monarchs to survive until spring. The annual cycle depends on destinations as well as the space between them.
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Eastern and western North American populations use different main wintering regions. Their movements should not be collapsed into one universal route followed by every monarch worldwide.
Slide 5
Several places share one population
Changes along breeding grounds, migration routes and winter sites can affect the same migratory system. No single location contains its entire life cycle.
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Monitoring at several stages helps interpret changes in numbers. A count at one winter site is valuable, but understanding causes requires evidence from the other places and seasons involved.
Sources
- The phenomenal monarch migration
US Fish and Wildlife Service
- Monarch butterfly species status assessment
US Fish and Wildlife Service