I was reading something about jigsaw puzzles that reminded me of a very difficult puzzle I did a long time ago that consisted of a white baby seal on an ice floe. Almost the entire puzzle was shades of white with just the seal’s eyes and nose being black. The image below is not from the puzzle but you can see why such a puzzle would be difficult.
While thinking about it, I was reminded of the cruel practice of killing baby seals, usually by beating their heads in with clubs, because their white fur is valuable.
The Canadian Marine Mammal Regulations that govern the hunt stipulate sealers may kill seals with wooden clubs, hakapiks (large ice-pick-like clubs) and guns. In the Gulf of St. Lawrence, clubs and hakapiks are the killing implement of choice, and in the Front, guns are more widely used (though clubs are frequently used at the Front to kill seals that have been shot and wounded).
It is important to note that each killing method is demonstrably cruel. Because sealers shoot at seals from moving boats, the pups are often only wounded. The main sealskin processing plant in Canada deducts $2 from the price they pay for the skins for each bullet hole they find-therefore sealers are loath to shoot seals more than once. As a result, wounded seals are often left to suffer in agony-many slip beneath the surface of the water where they die slowly and are never recovered.
This seems extremely cruel to me and I was surprised that the practice is still allowed.
A question occurred to me that had I had not thought of before and that was why baby seals are born white but adults are black. This reference source says that “Harp seal pups are born with long white fur that helps them absorb sunlight and stay warm while they’re still developing blubber. Pups shed their white fur after about three to four weeks old.”
But that puzzled me since white reflects sunlight while black absorbs it.
But other sources suggest that it is because the white fur enables them to better camouflage themselves during the first few weeks when they are confined to land to avoid predators, but they turn black after about four weeks when they start to spend time in the dark oceanic water.
As pups, harp seals go through several distinct stages. At birth they weigh about 10 kg (22 lb) and are called yellowcoats because their fur is stained yellow from amniotic fluid. After a few days, the yellowish tint disappears and their fur turns pristine white.
…During the first three or four weeks of their lives, seal pups cannot swim because their fur is not yet waterproof. As their mothers hunt (sometimes for as long as three hours at a time), the pups are left alone on the ice and tend to stay still in an attempt to blend into their environment. However, they remain easy prey because their mothers are unlikely to come to their rescue if they’re attacked. Once the pups have weaned, they’re left to fend for themselves on a regular basis as the adult females begin to mate.
The idea that white fur helps baby seals hide from their natural predators such as polar bears, foxes, and wolves makes more sense to me. Unfortunately, human predators are not that easily fooled.
When a Norwegian seal hunting inspector blew the whistle on some particularly cruel practicies in the 1990s the industry denied everything and he became ‘an enemy of the people’ in Norway. Much latter, other, retired seal hunting inspectiors confirmed he had been telling the truth.
Polar bears are also white, but their skin is black. Sunlight penetrates the white fur and allows the dark skin to absorb radiant heat. They obviously have no predators, so I assume the same principle applies to seals, and arctic foxes, in addition to the camouflage advantage.
The bears actually overheat and go swimming to cool off.
Was this your puzzle, Mano?
https://www.ebay.com/itm/296250505463?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&mkscid=101&itemid=296250505463&targetid=2299003535955&device=c&mktype=pla&googleloc=9221290&poi=&campaignid=21214315381&mkgroupid=161363866036&rlsatarget=pla-2299003535955&abcId=9407526&merchantid=114817641&gad_source=1&gbraid=0AAAAAD_QDh-pJYvwvmInpTbTm0soYOhml&gclid=CjwKCAjw1NK4BhAwEiwAVUHPULwMroPBdYIShRugY8VB81_2TqF1gVyIes1umUNSYgLld3CZa84MSBoCbkcQAvD_BwE
Crip Dyke,
Thanks for digging this up but I do not think that it was it. I seem to recall that the photo was taken mostly from the top so that the seal was on a sheet of ice with no real background.
But it was a long time ago and memories are notoriously unreliable. Mine may be exaggerating the difficulty of the puzzle.
Tethys,
Thanks for that insight. Do baby seals also have dark skin beneath the white fur? If so, then body warming would also explain it, thus providing two reasons for the color.
Two of my cousins used to be, maybe still are, jigsaw puzzle aces. I doubt they would have had much difficulty with our esteemed host’s white-on-white puzzle -- they preferred to work their puzzles face-down (the puzzles, not the cousins).
This may have facilitated their respective career choices, as university math instructor and lawyer.
Just for the record, while I strongly disagree with the seal hunt, the hunting of whitebacks (i.e. the really young pups with white fur) and bluebacks has been illegal in Canada since 1987.
You prompted me to have a look, Deanna. Quite so.
https://en.wikipedia.org/wiki/Seal_hunting#Regulations
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Not saying that The Humane Society of the United States (HSUS) is anything like PETA, but they’re not exactly an unbiased independent reporter.
#6: Aha, another puzzle freak! I too used to do them upside down, so I wasn’t distracted by pictures while studying shapes. My sibs once took a piece of safety glass, painted it white on one side, black on the other, broke it, and gave it to me as a puzzle. Yes, I worked it.
Mano
I can’t find anything on harp seals, but Northrrn seals also have pups with white fur, but their skin is a dark brown which matches their adult fur.
Judging by the black nose, lips, and snout of the harp seal in the photo, harp seals have very dark skin under their white fur. Zebras are all black too, if you shave them.
[OT
Zebra stripes ameliorating fly strikes is the most recent hypothesis; cf. https://www.nature.com/articles/s41598-022-22333-7
Me, I think it odd it’s evidently so rare in general. So, biggish grain of salt there]
The idea that the white fur is for camouflage rings true. But as far as colour for heating/cooling goes, I have never understood the oft-repeated idea that white clothes should be better for keeping one cool. Is there any evidence for that? My understanding is that white reflects heat as well as light, so I would expect light coloured outer clothing (or fur, over black skin) to be a better insulator to stop body heat from radiating away than dark, and consequently keep one warmer. In cold climates, a far greater amount of heat is produced by the body (for homoiothermic animals) than the surroundings, so insulation of body heat should be the most relevant factor.
Similarly, it’s common for people in hot regions to wear black. If black colour kept you hotter, I’d expect white to be more popular.
Tethys @#2
The World Wildlife Fund site verifies polar bears have black skin, and they also say the hairs of the fur are hollow. I have heard before the idea that the fur somehow channels sunlight to the skin, but WWF does not say that and I really doubt it. After all, white actually reflects all colors of light. That’s why it looks white to our eyes. I think the black skin might help the bear reabsorb infrared radiation coming from its own body heat.
Another reason I doubt the fur-sunlight idea is it is counterproductive. The sun only shines in the Arctic in the Summer months. The Winter is completely dark. So, for half the year polar bear fur cannot capture any sunlight, and might be actually “leaking” infrared light from the bear’s body heat. So it would keep the bear hotter in the summer and colder in the winter. Pretty lousy adaptation, if you ask me.
Optics is complicated
Strictly speaking, polar bears don’t have white fur: they have mostly transparent fur. But when you’re dealing with something that small and rolled up like an optical cable resulting in multiple angles in a small space, the net effect is something like the ‘frosted windows’ often used in bathrooms: there are all sorts of internal reflections and a good chunk of the incoming light ends up bouncing back out.
And now that I’ve already typed most of that I see Rob Grigjanis’ link says much the same thing but goes into more detail.
Rob Grigjanis, thanks for the article, it was quite interesting. I do note that nobody seems to remember that the Arctic is in the dark half of the year. So, even the ‘navigate using solar heating’ idea would still be worthless in the wintertime.
I still think the transparency of the fur is simply the way evolution gave the polar bear white camouflage. And I do tend to agree with the Chinese scientists that hypothesized the hollow hairs probably are for better insulation. Maybe the two traits are even connected, with the development of hollow hairs increasing the lightness of the fur color at the same time as it increased the insulation factor.
@Rob Grigjanis
Thanks for the very interesting link on the optical qualities of polar bear fur.
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I think the theory on snow-blindness is rather silly, as bears don’t have color vision, or particularly good eyesight in the first place. They rely on their acute sense of smell to locate seals or other food sources.
Hollow hair is a rather common trait in mammals, especially the ones that have to deal with arctic temperatures. I had heard the theory about fiber optics as regards polar bears, but I found that implausible.
Several people have already noted that their white fur is very translucent to light, rather than opaque like a white fabric. I don’t think they emit infra-red light under any circumstances, but it’s an amusing thing to picture. Heat energy can be seen by snakes, but I’m not aware of any mammals that can detect infrared.
It’s logical though unexpected that their fur also renders them invisible to infrared sensors. I’m sure the military could invent some very useful type of camouflaging that would also render people and machines invisible to infrared cameras.
Polar Bears evolved from Brown Bears, but unlike the Brown variant the Polar Bears don’t hibernate. Females do den up during the depths of winter to have their cubs.
It is relatively cozy inside a snowdrift, even when the air temperature is -60 F.
As far as the white fur goes, I don’t buy camoflouge, polor bears hunt mostly by smell. I do buy insulation though. Not the gathering of heat from the environment, but the reflection back to the skin of radiated heat. This lecture, which I find facinating in its own right is what first turned me on to this idea:
https://www.lenstreephotography.com/belkin.html
The speaker says in hot environs he would prefer a darker coat to help radiate heat off while the dog is running as he felt the acumulation of body heat was a limiting factor to endurance. It seems reasonable that a light coat would help with holding heat in.
Knowing rather intimately how grey hair has a different texture than brown hair, I was curious if the white fur of the baby seals was different in nature…and it is. It consists of a short fuzzy layer and long hairs, but also the hairs are frizzy and kinked meaning they will trap a lot of air in it. And that air is an excellent insulator.
But that doesn’t really explain why they’re _white_…unless it really is a matter of camouflage.