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A Model Migration
Photograph by Allison K. Shaw
To fully understand the cues individuals use and the decisions they make during the migration process, researchers must be able to track and manipulate individuals throughout their full migration. This is nearly impossible to do with most birds and mammals that migrate, but it could be easily done with Christmas Island red crabs. NGS/Waitt grantee Alison Shaw took the first step towards determining what cues red crabs use during their migration, and what variability exists in the decisions individuals make to migrate, especially with respect to key factors such as age, sex, and condition
Pictured: Tens of millions of red crabs inhabit Christmas Island in the Indian Ocean. The crabs' have a surprising and perilous migration from the island's interior to the sea.
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Making Their Way
Photograph by Allison K. Shaw
The word “migration” evokes images of vast numbers of animals on the move—from swarms of monarch butterflies clouding the sky to herds of wildebeest on the African plains. The question of how individuals migrate is thought to be one of the current top questions in science. Shaw examined the Christmas Island red crab's improbable migration to the sea, and the forces that prompt and guide all animal migrations.
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Traffic Jam
Photograph by Allison K. Shaw
Any crabs that don't migrate won't reproduce that year. Those conducting past studies noticed that there were a bunch of adults in the middle of the island during migration that weren't participating. I saw that myself while I was there, and the question came up: If you're a species that has to migrate in order to reproduce, why would you ever skip, why would you ever postpone?
Allison Shaw is a NGS/Waitt grantee. Read her full interview with NatGeo News Watch.
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Ready for the Journey
Photograph by Allison K. Shaw
"Some crabs are fully aquatic, some hang out on the beach and need to spend their time in the water, and some are fully terrestrial. All land crabs have eggs that have to develop in seawater, so all land crabs have to make some sort of trip back to the water."
Allison Shaw is a NGS/Waitt grantee. Read her full interview with NatGeo News Watch.
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Hanging In
Photograph by Allison K. Shaw
"My background is actually in applied math and biology, so a lot of my interests are in modeling as well. I talked to a bunch of people who worked on migration, and I discovered that most work on migration is done at a very specific level. People who study a particular species of bird study its migratory pattern because they're interested in that bird. Any summaries on migration that are done are done at a taxa level, so there are summaries of bird migration, summaries of fish migration, mammal migration, insect migration. But there's not much work that's been done to span different groups and to try to come up with general patterns of migration."
Allison Shaw is a NGS/Waitt grantee. Read her full interview with NatGeo News Watch.
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Standing Out in a Crowd
Photograph by Allison K. Shaw
"At the broadest level, animals are migrating because it pays for them to spend part of their lives in one area and the rest of their lives in a different area. That seems to be related to different food distributions, different levels of predation, different needs in their life cycles (so whether they need to be focusing on accumulating resources versus spending their times reproducing). It's generally understood that all those factors are important, but how they interact is less well put together."
Allison Shaw is a NGS/Waitt grantee. Read her full interview with NatGeo News Watch.
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Keeping in Touch
Photograph by Allison K. Shaw
"Before I learned about the Christmas Island red crabs, I had never heard of a land crab. The idea that there were these crabs that live in the rain forest and have to migrate to the ocean, but the adults can't survive in water, was a crazy concept for me. There are actually quite a few species of land crabs where the adults are terrestrial."
Allison Shaw is a NGS/Waitt grantee. Read her full interview with NatGeo News Watch.
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