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White Walkers: a warning letter from north of The Wall


As part of Matt Shipman's Science Carnival, I was invited to write a blog about the science of the Game of Thrones. Along with many talented science writers (check out their articles: Brian Switek, Jacquelyn Gill, David Hone, Miles Traer, Jesse Emspak, Raychelle Burks, Tara Smith ), I took on the task of trying to think of something interesting to say that could communicate some ecology at the same time. So I opted to write a letter to my mother as though I was in the Game of Thrones world, observing nature from north of The Wall. This is my first attempt into science writing - I hope you enjoy!!


Dear Mom,

I hope this letter finds you well, but it is with the utmost haste I am writing to you. Don’t worry, I’m not in any danger at the moment, I made it north of The Wall just as I had planned. Like you and dad suspected, the climb was arduous, windy, and terribly cold, but my layers of camouflaged gear allowed me to scale the wall undetected by the Knight’s Watch. I stashed my climbing gear in a snow cave about 500 meters from the wall and marked it with a GPS and on my map, just like you both taught me. I’ve been surviving quite well on a combination of the dehydrated foods you had me pack and fresh fish nearly every day. Anyway, now I’m in the wilderness north of the Wall, observing nature as I had hoped I’d be able to when I set out on this journey. It’s harsh but incredibly rewarding.

But the reason I’m writing is because I do believe that our ecosystem very well could be in peril due to an unforeseen threat. Read this carefully and please heed my warning: The White Walkers exist, mom. I’ll let you read that again, just to let it sink in, because I could hardly believe my own eyes when I first saw them. From a mountain cave through my spotting scope, I watched approximately 600 of them in a valley, ambling slowly toward the river (thankfully, away from my position); I suspect this was a relatively small group. Like stories I’ve heard of researchers observing wolves in Lamar Valley in Yellowstone Park, I watched their behaviors – in sheer terror, to be honest – firstly to stay safe, but secondly to gather data about their behaviors and life history. And after watching them from my humble abode for a few weeks, I have a lot of information to report; and I want your help to spread the word about the ecological repercussions of the White Walkers’ potential for range expansion.


The first problem is that winter is coming. While many people in our village and in Westeros have been saying this for years, few actually know what that means for the ecosystem and for our way of life. I am sure most people focus on how the weather will change and nothing else: it will get colder, we just need to wear warmer clothes, plant different crops, prepare to hunt different animals. Well, that’s just the beginning of our worries. White Walkers have always been affiliated with colder climates – so as colder temperatures are shifting southward toward the equator and King’s Landing, I expect the range of the White Walkers to shift southward, too. Something similar happened on Earth, where the climate actually got warmer on average over a very short period (~200 years). One particular example was the south-ward shift in the range of a seabird called a Gentoo penguin, to nesting locations on the Antarctic Peninsula. The Gentoo penguin is associated with warmer, sub-Antarctic waters and prefers the open ocean for hunting fish. However, over the course of only ~20 years researchers began seeing more gentoos nesting in areas where their ice-obligate brethren – the Adélie and the chinstrap penguin – used to call their homes. What happened in that case is the sea ice distribution around the Antarctic Peninsula began to decrease substantially with increasing air and water temperatures, and the Gentoo penguin moved right in and made itself at home... A climate change winner. Conversely, the Adélie and chinstrap penguins require sea ice near their nesting habitat on land, so as the sea ice shifted their populations followed.

Gentoo penguin (c) Michelle LaRue

The fact that warmer climates affected a few penguin species by way of shifting sea ice distributions is only one of literally hundreds of examples of the effects of climate change on ecosystems. So just as was observed on Earth, in our case in Westeros, we should see more White Walkers farther south than we have in thousands of years as the climate gets colder.

And what are we to expect? Will the range expansion of White Walkers displace other species, or will other top predators experience niche partitioning? Should we expect to see changes in the biodiversity of our ecosystems? Which species are likely to be their biggest competitors, and what is likely to be their preferred prey? Will they utilize dispersal corridors the way many large animals do, or will their range expand randomly upon the landscape? These questions, simply put, are terrifying to consider.


The mere fact that the White Walkers are cold-adapted species isn’t the only issue: their populations seem to be entirely unregulated and that’s a horrible, horrible problem. We always learned in school that theoretically animal populations could grow at a constant rate forever and eventually their populations would reach infinity. For example, if you started with 100 white-tailed deer in a population that grew 10% annually forever, in year two you would add 10 deer resulting in 110 total in the population, and year three would have 121 deer… and so on until you have nearly an infinite number of deer. This is called exponential population growth.

However, with the exception of short time frames in a population, exponential population growth is generally not observed in nature because there tends to be some factor that keeps the population in check; populations can only get so big and when they do, they have reached what we call the population’s “carrying capacity” (or K for short). This is called logistic growth. So whether it’s disease, habitat availability, food resources, or predation, populations tend to be regulated in some way.

White-tailed deer (c) Michelle LaRue

Except for White Walkers. I have watched their populations grow substantially since I’ve been here, with seemingly no end in sight. Their form of reproduction is unique: if a White Walker kills you, you can then come back from the dead and be turned into a White Walker. Given their other-worldly strength and resilience I don’t see any way their populations could be stopped. An unregulated population like the White Walkers, in the colder climate we’re headed for, could easily expand and demolish southern ecosystems. Because they seemingly can kill anything, their tenure farther south could mean total decimation of the forest communities, which would no longer have predators to keep herbivores in check. Or, over time, dispersal of certain seeds could be halted entirely due to no more herbivores or frugivorous birds in the forests, ultimately changing the forest structure. Their expanding, exponentially-growing populations would be no match for even dragons or people, as I’ve only heard – but not seen myself – that Valyrian steel or dragon glass are the only weapons that can kill a White Walker. And you know how few Valyrian steel swords are left in the world.

Probably the most dangerous thing about White Walkers isn’t their cold adaptations or their unending population growth. It isn’t just the fact that they seem incapable of death. What’s most dangerous about White Walkers is that people still do not believe they exist. We’ve heard tales about them from centuries ago, and the stories get bigger and more ridiculous as time goes on, lord knows. But it is now time to spread the word: I have evidence of White Walker populations; I know their behaviors and have watched them over the last few weeks. These weird humanoids could be deadly to our ecosystems and I can’t foresee anything standing in the path of their ecological destruction...

Except evidence-based, accurate communication. I have enclosed several photos for you to share as critical pieces of this evidence. We must talk to people about their existence and the dangers associated with their range expansion. The probability of the seven kingdoms banding together to fight the White Walkers together is a pipe dream, I know. Even the probability of locating the proper swords with which to fight them is exceedingly low. But we must try. We must try before it is too late and their populations have gotten to a critical mass where their takeover is inevitable. Otherwise, I’m confident that our existence and the ecosystems in which we live will be irreparably changed. And given we have enough warning time, we absolutely must try to stop them; for the health of our ecosystems and the well-being of humanity, we must try.

Your daughter,



A Storm of Chemistry by Raychelle Burks

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