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How do birds know when it is time to fly north after the winter

8 Answers
My children in preschool asked this question today. We talked about when the birds migrated but they wanted to know how the birds knew when it was time to return North.
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Birds actually do not have an annual clock. Instead they have a translucent skull and a pineal gland that responds to the amount of light that get through the skull and interacts with the chemicals in the gland. The more light there is, the more of certain hormones build up in concentration which then initiates the correct migratory behavior. This was verified in studies where skull caps were place on migratory birtds to prevent light from entering the skull. Such outfitted birds lost all ability to determine when to migrate. This same research led to a breakthrough in understanding human behavior as it was determined that human beings rely on light interacting with our pineal gland to produce melatonin whin, in turn, affects our mood -- people with less melatonin are often more lethargic and depressed. So, how does the light reach our internally embedded pineal gland? Via our eye sockets believe it or not1 It explains why there are higher degreees of depression and anti0-social behaviour in regions of the USA known for having very litle cun.

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Birds that migrate follow the food. Species that migrate short distances, such as ducks or robins, will return to their breeding territories as the insects and plants bloom in that area. Birds that migrate long distances, such as humming birds or tundra swans, begin migration triggered by day length, temperatures and genetic predisposition. They follow available food as the spring weather marches northward and pause to rest at spots along the way. The famous sandhill cranes that converge on the Platte river in Nebraska rest and fuel up on food for about a month before continuing their journey to Canada and Siberia.

http://www.birds.cornell.edu/AllAboutBirds/studying/migration/
http://www.rowesanctuary.org/crane%20facts.htm

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In other words, no one knows how they do this.

There is an even more amazing migration: that of the Monarch butterfly. The Monarch winters in the mountains of Mexico. At some time in the Spring, it migrates to Texas, breeds and dies after putting their seed on a plant leaf. The offspring then mature, become butterflies and fly north some more, living about a month. They breed and die. The next generation does the same thing, eventually arriving in northern US and Canada. They breed and die after living a month. The 4th generation hatches (caterpillar), matures and becomes a butterfly. This is now the Fall. This generation then migrates 2000 miles back to Mexico. The trip takes 2 months. They spend the Winter in Mexico. How about that?

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Long distance migrants have an internal clock that controls the onset of migration and the pre-migration preparations. Environmental factors set this clock and keep it fine-tuned. It is thought that certain changes in a bird?s environment stimulate the production of hormones, which in turn lead to changes in the behavior and physiology of the bird, preparing them for migration.

Southbound migration timing may be fine-tuned by changes in day length. The environmental factors operating on the wintering grounds, where day length is relatively constant, are more subtle and less well understood.

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Oh yeah...

Well up until my age of about twelve my Father would pile us all in the car every year and head South to Florida... after about two weeks we'd turn right around and head back North... we always wondered how Dad knew it was time to go home... can't explain it. He just knew... LOL.

yes is right, Ballot - somehow birds and butterflies just know... and science has yet to wrap it's collective brain around it. Though I am interested to know what some of your students thought the reasons were...?

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Scoop, you aren't thinking that your father had a bird brain.

Birds and butterflies, certainly don't remember the date, and they don't have much brain to start with, so it is a real mystery.

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My last sentance didn't make it into my answer, sorry:

Researchers think birds have a yearly clock in their brains that tells them it is time to fly home...

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Certainly not, he was brilliant - but at twelve I thought he was quite the mystery. Amazing how our parents get smarter as we get older...

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