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zakur · 2nd July 2003, 02:49 PM

Quote:

Dung Beetles Navigate by the Moon, Study Says

Out on the African savanna, a fresh and moist pile of fine-grained antelope dung is a nutritious treasure aggressively fought over by a melee of critters. The spoils go to those with the craftiest strategies to snatch and stash a piece of the pie.
To gain an edge in this battle for the poop, the African dung beetle Scarabaeus zambesianus orients itself by the polarized light pattern cast by the moon to make a straight, nighttime escape with its morsel, according to Marie Dacke, a biologist at the University of Lund in Sweden.

[...]

Many creatures are known to use the polarization pattern of sunlight to navigate, but S. zambesianus is the first animal known to use the million-times dimmer polarization of moonlight, Dacke and colleagues report in the July 3 issue of Nature.

Bruce Gill, an entomologist and dung beetle expert at the Canadian Food Inspection Agency in Ottawa, was at first surprised by this beetle's behavior, but upon reflection he said it makes sense because light from the moon was simply reflected sunlight, and many insects that are active during the day are known to navigate by polarized light from the sun.

More on this crappy study here.

ceptimus · 2nd July 2003, 03:13 PM

What causes moonlight (or for that matter sunlight) to be polarized in the first place?

ceptimus.

CapelDodger · 2nd July 2003, 03:28 PM

Reflected light is polarized parallel to or normal to (damned if I can remember) the surface it reflects off. So light reflected off the Moon is polarized. Don't know about the Sun though; some sort of magnetic effect from the solar wind or Earth's magnetic field?

uneasy · 2nd July 2003, 11:57 PM

Drat, you mean I have to hide my dung even at night or dung beetles will get it?

I really dislike scientific articles that say "When the scientists did this, the test subject did this!" Wahooo! Every single one of dem beetles every single time? Somehow I doubt it. What were the real statistics? I don't care if it was 99%, just tell the actual numbers please.

Maybe they do have some abilities. Animals are shown to be smarter all the time (to the terror of creationists). But it seem fishy. Or is that dungy?

MRC_Hans · 3rd July 2003, 04:25 AM

Sunlight in itself is not polarized, or to be absolutely precise: It contains light of all polarities. However, the light from the rest of the sky is reflected sunlight and it IS polarized. Look at the sky through a polarizing filter (polarized sunglassed will do), turn the filter, and you will se the light intensity change. This works even on an overcast sky (although the effect can be much diminished, depending on conditions). The ancient "sunstone" used as a navigational aid in medieval times and earlier is a crystal that can show the polarization of the light from the sky, and enable the user to find the direction to the sun, on a cloudy day.

Hans

CapelDodger · 3rd July 2003, 06:51 AM

Quote:

However, the light from the rest of the sky is reflected sunlight and it IS polarized

Thank you for that Hans.

So if these things are so clever, how come ...?

2nd July 2003, 02:49 PM	#1
zakur Illuminator Join Date: Aug 2001 Location: Dayton, OH Posts: 3,265	Study: Dung beetles navigate by moonlight Quote: Dung Beetles Navigate by the Moon, Study Says Out on the African savanna, a fresh and moist pile of fine-grained antelope dung is a nutritious treasure aggressively fought over by a melee of critters. The spoils go to those with the craftiest strategies to snatch and stash a piece of the pie. To gain an edge in this battle for the poop, the African dung beetle Scarabaeus zambesianus orients itself by the polarized light pattern cast by the moon to make a straight, nighttime escape with its morsel, according to Marie Dacke, a biologist at the University of Lund in Sweden. [...] Many creatures are known to use the polarization pattern of sunlight to navigate, but S. zambesianus is the first animal known to use the million-times dimmer polarization of moonlight, Dacke and colleagues report in the July 3 issue of Nature. Bruce Gill, an entomologist and dung beetle expert at the Canadian Food Inspection Agency in Ottawa, was at first surprised by this beetle's behavior, but upon reflection he said it makes sense because light from the moon was simply reflected sunlight, and many insects that are active during the day are known to navigate by polarized light from the sun. More on this crappy study here.
	__________________ "I do not believe in the collective wisdom of individual ignorance." -Thomas Carlyle "That's the problem these days: nobody thinks of the tumors." -steinhenge

2nd July 2003, 03:13 PM	#2
ceptimus puzzler Join Date: May 2003 Posts: 3,316	What causes moonlight (or for that matter sunlight) to be polarized in the first place? ceptimus.
ceptimus puzzler Join Date: May 2003 Posts: 3,316

2nd July 2003, 03:28 PM	#3
CapelDodger Penultimate Amazing Join Date: Sep 2001 Location: Cardiff, South Wales Posts: 16,761	Reflected light is polarized parallel to or normal to (damned if I can remember) the surface it reflects off. So light reflected off the Moon is polarized. Don't know about the Sun though; some sort of magnetic effect from the solar wind or Earth's magnetic field?
	__________________ It's a poor sort of memory that only works backward - Lewis Carroll (1832-1898) God can make a cow out of a tree, but has He ever done so? Therefore show some reason why a thing is so, or cease to hold that it is so - William of Conches, c1150

2nd July 2003, 11:57 PM	#4
uneasy Muse Join Date: May 2003 Posts: 504	Drat, you mean I have to hide my dung even at night or dung beetles will get it? I really dislike scientific articles that say "When the scientists did this, the test subject did this!" Wahooo! Every single one of dem beetles every single time? Somehow I doubt it. What were the real statistics? I don't care if it was 99%, just tell the actual numbers please. Maybe they do have some abilities. Animals are shown to be smarter all the time (to the terror of creationists). But it seem fishy. Or is that dungy?
uneasy Muse Join Date: May 2003 Posts: 504	__________________ Mud, Mud, glorious mud Nothing quite like it for cooling the blood!

3rd July 2003, 04:25 AM	#5
MRC_Hans Penultimate Amazing Join Date: Aug 2002 Location: Whithin earshot of the North Sea Posts: 16,604	Sunlight in itself is not polarized, or to be absolutely precise: It contains light of all polarities. However, the light from the rest of the sky is reflected sunlight and it IS polarized. Look at the sky through a polarizing filter (polarized sunglassed will do), turn the filter, and you will se the light intensity change. This works even on an overcast sky (although the effect can be much diminished, depending on conditions). The ancient "sunstone" used as a navigational aid in medieval times and earlier is a crystal that can show the polarization of the light from the sky, and enable the user to find the direction to the sun, on a cloudy day. Hans
	__________________ Don't. Just don't.

3rd July 2003, 06:51 AM	#6
CapelDodger Penultimate Amazing Join Date: Sep 2001 Location: Cardiff, South Wales Posts: 16,761	Quote: However, the light from the rest of the sky is reflected sunlight and it IS polarized Thank you for that Hans. So if these things are so clever, how come ...?
	__________________ It's a poor sort of memory that only works backward - Lewis Carroll (1832-1898) God can make a cow out of a tree, but has He ever done so? Therefore show some reason why a thing is so, or cease to hold that it is so - William of Conches, c1150