In the waters of Iceland, the natives have their own word for a particular brand of cetaceans--"Illhveli", literally "evil whales". And the bloodthirstiest of them all is Raudkembingur, Icelandic for either "red comb" or "red crest".

Now, the outlandishness of some mythological animals is so minimal that in an alternate Earth where such creatures are real, their existence can be justified biologically, physiologically, anatomically and even evolutionarily. (For example, the "eagle-talons" of an enfield can be explained simply by some propaganda artist looking at an ordinary canid with raccoon-like front paws.)

Even so, a predatory toothed whale as big as a sperm whale with a bright red head is a bit odd and not so straightforward to justify. Why would such an apex predator need a red head?

• Its actually really easy to justify. Nine times out of ten when you see something weird in biology is has to do with sex, and a difference like the one you want is pretty easy to justify as sexual selection either for male display or species recognition. – John Jan 9 at 4:24
• Because red things go faster of course! – Arcanist Lupus Jan 9 at 4:29
• @John Quite true, but water cuts out that end of the spectrum - attenuation of red wavelengths comes first and increases with increasing depth. You'd need to be talking about an advantage near the surface or other source of red light. – Tantalus' touch. Jan 9 at 4:32
• @Bitterdreggs. Plenty of animals do their display in particular places, in this case the surface, it could even be part of breaching display that happens to make it dangerous to small ships not from malice but just do to violently breaching a lot during hte mating season and damaging vessels. breaching is already a possibly display practice. And whales have ot surface regularly to breath anyway so plenty of time spent near the surface. – John Jan 9 at 4:42
• Maybe it's like flamingos, the color isn't genetic, it comes from what they eat. Your whale feasts on the blood of Christians. So it acquires a red pigment. The reddest whales are the most deadly. – workerjoe Jan 9 at 14:25

## To hide in red water

Now, water is not usually red. But one of Raudkembingur's primary prey creatures is another whale, but this whale is a filter feeder whose primary diet is red tide algea blooms. As such, the Raudkembingur has evolved a red head to conceal itself while hunting these other whales amidst the red tide.

(Presumably this is an alternate world where red tides are regular enough to support a stable population of whales.)

• I was thinking something similar - this reminds me of how some fish have white underbellies that make them harder to see from below when looking at the bright ocean surface. +1 – Zxyrra Jan 9 at 5:15
• I like this answer a lot. It adds an awesome creepy factor to any area where the whale might appear as well. A blood-red sear sloshing gently beneath the boat, listening to the dull sounds of waves smacking the wood, until suddenly-- a massive whale with a bloody red head springs forth without warning! It also gives an implied "safe zone" wherever red tide isn't, so that someone might relax and let their guard down, only to be terrified when the 'rules' of the whale are broken and they're attacked somewhere that might make less sense. – NegativeFriction Jan 9 at 13:25

The same reason as other animals have large crests the the like; Display

Male Peacocks get no hunting or camouflage advantage from their large bright tails. It actually makes them less agile and less able to slip through scrubby terrain than peahens for example.

Roosters again get no benefit from their combs, nor lions from their manes, nor deer their antlers, for hunting or any other form of sustainment or protection.

They do, however, turn on the ladies.

Ultimately, these are all forms of display intended to attract the attention of the opposite sex for mating purposes. Ideally, it also serves to put off other males by having a display that means they're less likely to confront you because you look bigger and cooler than they are, meaning in turn you spend less energy fighting your own kind for the right to mate that you could use defending your mate or your young or even better yet hunting.

What you'd probably find is that these red heads are far more pronounced on the male of the species, who use them to impress the females and advertise how fearsome they are without actually having to fight to prove it. It does however also mean that these whales are less likely to be ambush predators as they would find it hard to hide.

In lion prides, it's often the lionesses who hunt for that very reason; they're better at camouflage and therefore can set group-based ambushes so much more easily than the males can. My guess is that the same would be true of your whales and that if they are in any way a pack animal in which case the males are effectively attacking for reasons of protection and territory defence.

Even if they are solitary animals, the crest would likely stave off attacks from other similarly sized predators or even keep females out of their territory other than for mating purposes so as to let them protect their own hunting grounds.

• red won't make it that hard for them to hide depending on how deep they hunt, red light does not penetrate far. – John Jan 9 at 4:44
• I’m pretty sure that deer antlers can be used to defend against predators- a wolf that gets gored by a charging elk is probably going to be severely injured. – nick012000 Jan 9 at 7:15
• Deer antlers are often used for protection in the tough winter months when they can't easily run from predators. Lions' manes probably help protect their necks in fights between two males. – user39548 Jan 9 at 14:47
• You can add the narwhal tusk to that list. (There are lots of excited web articles suggesting that tusks have an actual function - but only males have them, and females live longer. If their primary purpose was fish stunner/water taster, they'd be present in both sexes.) – Martin Bonner supports Monica Jan 9 at 16:09
• Roosters again get no benefit from their combs No, but the rest of the flock does. – Draco18s no longer trusts SE Jan 9 at 18:57

Why are flamingos pink?

Perhaps it's not evolutionarily desirable at all - the whale's favorite prey simply includes a natural red dye that turns the whale red. Older and more powerful whales would, of course, naturally accumulate a deeper red color over time...

Other answers have already concluded that your world needs an extra common red tide, so maybe you can trace the food chain all the way down to that as the initial source of the dye...

• As I understand it, flamingos are genetically gray, but some wild groups turn pink due to their diet. Flamingos in zoos are fed special diets explicitly to turn them pink. – BlueRaja - Danny Pflughoeft Jan 12 at 1:27

With the more out-there ideas bolded.

Reasons for heritable characteristics may be:

• To keep from being eaten. I know, I know, they are big and bad, but maybe there's something bigger and badder. Even if it doesn't prey on them when they get larger. It can be an artifact of defense from when they were little.
• Camouflage obviously. To hide in an environment where the color is good for that.
• The red stuff is actually whatever that defense's color. Whether it be stinging anemones that simply hitch a ride and sting whatever might mess with them or...hey actually if they have a symbiotic relationship, the stinging stuff that grows on them can be a defense to start with, but later in life might actually stun prey.
• To make more. Sex. The most outlandish things on animals are generally sex-selection during mating. The display of such generally proves fitness. Included to be complete and the most boring entry, but...I would make this an answer even if there are other reasons as well.
• To eat more. Food. This makes it easier/more efficient to get food.
• Camouflage in order to hunt. Red tide will be brought up, but you ought to also look into the colder version of that: the Artic's Red Snow Algae They can lay in wait near shorelines ready to take seals and so forth. This would be specifically for ambush predation, whatever form it takes.
• To gather food/resources. The hairs aren't actually hairs. Your creatures are bloodthirsty because they feed on blood in the water that they swim through. This is gathered and specially preserved or kept, perhaps in addition to meat they eat. Not much in the way of earth science to support that, but...this is NOT earth.

And finally, don't be afraid to mix it up. That is, just because there's one function, doesn't mean you can't have others! The redhead can be sex-selection AND a gruesome blood sponge!

What about a symbiotic relationship with some kind of red algae? The red algae lives on the whale, where it gets protection and a steady supply of sunlight as the whale chill out in the surface water. In return, the algae produces some antibiotic that protects the whale or supply the whale with extra nutrition.

I made a quick search for algae-mammal symbiosis and found this article about a green alage in the fur of the sloth that provides the sloth with nutrition through absorption through the skin, and in return gets a safe and humid place to live.

• I like this approach, and lends itself to riddles "what colour are the red whales of X planet?" - grey. – Vix Jan 11 at 17:07

## Age and Power

If I am reading your question correctly, there is an entire species of carnivorous whales and the Red Crest is a single member of that species. If that is wrong and the Rest Crested Illhveli is the species, then I would go with Tim B II's answer about mating displays.

So, assuming that you want to know why a single member of a species would have such a distinctive display, I would suggest that it is because that is the oldest and most powerful member of the species that humanity has encountered. Think of it as an extreme example of something like the Silverback Gorilla. All Illhveli slowly come into their red crest with age, but between their long lives and extreme competition for resources few are able to actually live long enough for it to be noticeable.

## Sudden Acts of Violence

A predator the size of a whale would obviously be in constant search for its next meal, and the older it gets the more experience it would have in hunting in the most efficient manner possible. Which will most likely be long periods of little to no activity followed by bursts of activity when prey is nearby. Drawing another parallel to real creatures, it would be similar to how crocodiles or alligators behave. Minimize energy expenditure by floating along until prey is nearby, then explode into action to subdue your meal. As long as you get more energy from your prey than you spent finding it, you are good to go.

From a human point of view, this is going to look absolutely terrifying. Ships that run into Red Crest would not know that they were in danger until it was far too late. The only thing they would see is a sudden disturbance in the water, if that, and then the ship being demolished around them and anyone in the water being consumed. At the same time, Red Crest is unlikely to attack more than one ship at a time as long as they are suitably spaced out, since that is not how ambushes work. So you have plenty of opportunities for superstitious sailors to see other ships attacked while being relatively safe themselves. Thus the myth of the Red Crest is formed.

## Passing the Torch

The final benefit to the red crest being a feature of age is that it inherently allows the Red Crest to always be a threat. One single animal, no matter how dangerous, is a finite threat. Eventually time will take care of it for you. But if the Red Crest is just the oldest and strongest member of it's species, then there will always be the chance for a younger upstart to challenge that position. Depending on what you want for your story this can be a known phenomenon, a complete mystery, or a shocking discovery. There are benefits to however you want to play it.

Knowing about the Red Crest as a title means any time a challenger shows up your sailing lanes just got twice as dangerous. Not only is there another predator around, but the fighting from these two massive creatures could cause disruptions even if they ignore your ships. If the fighting happens out of sight and people never find out, then there is just a giant immortal muderwhale always lurking out of sight waiting to take its due from unwary sailors. I personally like the discovery story though since it can lead to a really exciting reveal. Just when a sailor thinks that they are a goner and the Red Crest is going to get them, a slightly smaller and less red whale attacks the Red Crest and "saves" the day.

Mate attraction really is probable for a colorful display on a large animal.

In deeper water, it's still a high contrast black-white pattern; this is perfectly good for species and individual recognition. Whales are required to ascend to the surface, and so having the red pigment isn't pointless. If mating behavior occurs near the surface (which it does in many whales because swimming up and down for air mid-sex is counter-productive) then the color will be most visible at the time when it's most important.

Intensity and density color is usually an Honest Signal of immune system health to prospective mates.

The crest as illustrated seems to introduce some drag problems - it may be an Honest Signal of fitness to prospective mates, like a peacocks tail: "I can still hunt even with this ridiculousness on my head, you should mate with me!"

The spikes may be mostly fleshy, rather than bony, and they're only erected or extruded as part of a threat display. There's many animals that inflate weird structures as sexual displays or threat displays. The bright color may be mostly dull brown, but turn bright red as part of the same threat display, and the crest is erected at the same time. This would work deeper down as well as near the surface, and seagoers would associate the bright-red "spiky" whale with aggression.

Threat displays are useful within the species (when contesting territory and mating rights) and without the species (chasing off competing predators, defending young, etc.)

If the whales aggregate in "birthing pods" and "nursuries" near the surface, you'd have large groups of whales in a highly defensive mood, and they may attack nearby ships to drive them away from the young. Young whales may not be agile enough to evade boatstrike, and they'd have to learn the behavior - adult whales are certainly smart enough to know about boatstrike and to know its a risk to the babies.

# Invisibility as an ambush hunter.

When not near the surface, red appears to be black since all the red light has been filtered out by the water above it.

I would think that this whale waits below the expected depth of its prey in a head up attitude. This would make it look just like the dark water below it.

### Also, the reason for the whole whale to not be red:

From below, it wants to look lighter and bluer since then it will be camouflaged against the brighter water above it.

It's not so much a need as a marker of ferocity and feeding frequency. The red color is from accumulated scar tissue from attacks on boats and beaches to reach prey.

I have a book that approach the subject of flora and fauna perception of colors.

Here are some interesting facts :

• Plants have a light receptor that is only sensible to red. Apparently, lighted by red light, plants can grow faster and higher. You could use the same approach for your whale : the red color on it's head could attract food (very little fish) for example.

• With mondrills (large monkeys), red is used as a signal for domination or agression. It bring statue and communicate the fighting capacities. More red equals more agressivity.

• The chaffinch (small birds) that have red feathers tend to dominate those with black feathers. "These birds seems to have a natural fear of red" (S.Pryke, 2009)

The mane is an oxygen exchange organ.

Adapted from my answer Could a land vertebrate re-evolve gills after moving back into the water?

There are lungs and there are gills. There are some other ways to get oxygen as well. Some animals respire through the skin. Behold: the Hairy frog.

https://en.wikipedia.org/wiki/Hairy_frog

These frogs do gas exchange through their well vascularized dermal papillae.

For an example of a mammal with gills, one could consider Heuvelman's cryptid merhorse.

from In the Wake of the Sea-Serpents.

The merhorse: an elongated sea animal of large size characterized by a sort of large mane hanging down it's neck.

It is it may seem surprising that there should be a semi-abyssal mammal living at a fairly considerable death of up to 100 fathoms. It is here that their mane, so very unusual in a sea animal, make come in. It is noticeable that the better adapted an animal is to life in the sea, the more hairless it is; the cetaceans are smoother than the pinnipeds and even in the fur seal the mane is very short. Ivan Sanderson has suggested to me that the mane of these sea serpents might be respiratory organs in the form of filaments, , similar to the hairs of the hairy frog similar to the hairs of the "hairy frog", and supplementing their pulmonary respiration. And in the merhorse as in the hairy frog these hairs are reddish which may perhaps be due to their structure and function. But, admittedly, this arrangement would be quite unique among mammals.

Of course the merhorse is a theoretical cryptid. But the rationale of a vascularized "mane" of dermal appendages makes sense. The animal (the merhorse is a mammal; possibly a pinniped) spends a great deal of time at depth (as evidenced by its huge eyes). If it could do some gas exchange at depth through vascularized skin, that would let it stay down longer before resurfacing. It could hunt, or hide, or do whatever it needed to do in its deep home.

Some pinnipeds do have very vascular secondary sex organs akin to rooster combs - here is a hooded seal showing off his.

If the merhorse (or the red maned whale) gained greater fitness by increasing the size of its respiratory skin appendages, they could increase and proliferate until they formed a manelike covering. It is not a gill in the fish sense, but it has converged on the function of an external gill like that of a worm or an axolotl.

I think a very big animal would probably derive little selective benefit from slightly more gas exchange area. Probably this would first arise in a small seal. Once the vascular mane was established as helpful to a small animal, it could be selected for larger sizes, culminating in the large merhorse. Or the red mane of the red headed whale.

• Why don't you like this one, Dailey? Usually you post some kind of reason. – Willk Jan 18 at 23:45