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Around this time of year, I always have to take a break from pumpkin planning and marvel at bird migration. How do they find their way around the world without Google Maps? We’re not really sure, but research has given us evidence that they use an array of navigation techniques…
1. Migratory reflex and navigational skills appear to be written in the genes. Captive birds have been observed getting pretty fidgety and changing their sleep patterns right before their natural migration time. Ethologists – those who study animal behavior – call the birds’ behavior zugunruhe (“migratory restlessness”). Captive birds display zugunruhe even if they’re not exposed to natural light or to seasonal temperature changes. Even with the restlessness, many of these birds will orient themselves in the direction that they would normally be traveling at that time of year. Researchers say that the fact that the birds know both when and where to migrate without environmental clues suggests that genes, and a biological calendar written into them, play a role in migration.
2. Genes are all well and good to get them started, but how do birds navigate once they get up in the air? The prevailing theory is that the earth’s magnetic field plays a large part. Over the last few years, scientists have discovered tiny bits of magnetite – a magnetic mineral – in the brains of several animal species, including birds, bats, whales and dolphins. The magnetite could enable the animals to use the earth’s magnetic fields as a migration guide, but the research is just scratching the surface. Now that we know that birds and other animals could detect magnetic fields and have explored the mechanisms by which they could do it, further research will need to tackle the question of how the animals gather information from the magnetic field, process it and use it to navigate.
3. A particularly cool study showed that migratory birds also use “celestial navigation” to find their way around in the dark. Captive birds placed in a planetarium changed their directional orientation when the star pattern on the ceiling shifted and became confused when the images of stars were dimmed. The scientists conducting the experiment suggest that birds use the layout of constellations in the sky as a compass.
But why migrate in the first place? And why do birds bother flying back north once they’ve reached a warmer locale? The same reason I have to pull myself away from writing and go to the bodega on the corner: the search for food. While birds might be hard-wired to migrate at certain times of the year, a recent study concluded birds won’t make the trip without certain physiological and environmental cues, the most important being the scarcity of food. Birds fly south in the winter in search of alternate food sources, and even though their summer home might be nicer, they return home in the spring when their usual food stocks are replenished. If there’s still food to be had at either place, though, some birds will delay migration or won’t bother leaving at all, choosing instead to band together in flocks to forage.
This article originally appeared last fall.
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Comments (11)
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4. It’s too far to walk,
posted by partiallyDeflected on 9-29-2008 at 7:34 pm
Zugunruhe!! My seasonal restlessness has a fancy name, I’m sooo happy. I’m so inserting this word into every conversation today.
posted by Angelia on 9-30-2008 at 8:46 am
I think it’s incredibly cool that you could put a flock of birds in a planetarium and get useful data…
posted by Jim on 9-30-2008 at 12:04 pm
Re: Why do they migrate?
So how did the first bird know where to go? Not to spawn another Creationist debate, but this essay has me intrigued about how migration fits in the evolution theory. How did the first one start? How did the first birds know their was food in S. America, or wherever, to begin with? Better yet, how did they know there would be a S. America there when they got there? And then once they figured that out, how do they come up with migration groupings? Are they all just one big extended family? Is it a social network that joins up like a Club Med cruise? Or is their a clique that forms and they choose a pecking order who gets the aisle seats? How did migration all start? And why not land creatures? It’s not like we don’t have the same needs for food and warmth. No doubt it takes longer, but if you don’t know how far you’re going to begin with, what’s stopping you? Do we all have this magnetite too and we’ve just trained ourselves not to listen? If humans were enclosed in dark rooms and asked to face south, would we know?
How fish developed fins and birds developed wings is awe-inspiring to begin with but still imaginable, but to figure out how migration is actually written into the genes is mind-boggling. How does evolution write, “Go to eat guava in Acapulco in November,” into the genes of something that’s never been to Acapulco, and never seen a guava, via a lump of rock that forms in the brain. Also, does the sensitivity of the magnetite increase under certain environmental conditions, or does the magnetic resonance of their destination increase on the other end, or both?
Fascinating article. More questions than answers. Please floss soon.
posted by j hillary on 9-30-2008 at 5:02 pm
do humans have magnetite?
posted by Aurora on 10-18-2009 at 1:18 am
Bodegas have food? I thought they sold weed.
posted by CJ on 10-18-2009 at 8:28 pm
This may seem like a dumb question, but do birds in the southern hemisphere fly north for the winter? I.e. do all birds fly north and south at the same time every year (think about it– northern birds would fly south for their winter, the same time southern birds would fly south for their summer)?
posted by Joel on 10-19-2009 at 8:43 am
When geese fly in a V formation why is one side always longer than the other?
…because there are more geese on that side. :)
posted by Christine on 10-19-2009 at 10:01 am
j hillary:
Don’t worry – you won’t spawn another Creationist ‘debate.’ Creationists are imbeciles who try desperately to equate science with religion, and they can never succeed. It doesn’t matter what scientists don’t know, or don’t know yet. That scientists don’t have an answer to a particular question does not strengthen Creationist ‘debate.’ Science is an on-going process of learning. Creationism is purely story-telling.
posted by Bubba on 10-19-2009 at 11:02 am
So, Bubba, you do not have an explanation of your own. You are merely convinced that whatever the other people are saying, they must be wrong.
That sounds like a slavish adherence to a doctrine…
posted by Logician on 10-19-2009 at 11:59 pm
Birds also fly North for the winter!
Migratory birds swap hemispheres each time the weather starts getting cooler, so they live in perpetual summer.
Some of them even do their breeding and fledging in the Southern hemisphere, so their first journey is northwards.
posted by AJW on 10-20-2009 at 12:07 am