Kaibab Squirrels - Grand Canyon's Most Charismatic Mammal?

Behind the Scenery

What are Kaibab squirrels? How rare are they? How can I see one? Join this conversation with Houston Thompson, a wildlife biologist at Grand Canyon, to learn what we know about this special species, what’s still to be discovered, and what makes them so darn cute!

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TRANSCRIPT:

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Houston: You want to go out and see one? You're probably going to need to hike some miles. Maybe go for some drives, and you're just actually going to have to get lucky.

Juli: Hey there. I'm Ranger Juli, and I sat down with one of our wildlife biologists to learn more about just one of the many things that make the North Rim of Grand Canyon a special place, Kaibab squirrels.

Houston: Yeah. Hello. My name is Houston Thompson. I'm a wildlife biologist here at the Grand Canyon. Working on the North Rim in summers focusing on our Kaibab squirrels, our bison, Mexican spotted owls, and California condors, in addition to a number of other critters. Been here a couple of years and we've been making great strides, especially on some Kaibab squirrel population modeling. And that's what we're here to talk about today, I believe.

Juli: Awesome. So what are Kaibab squirrels and why is it important for you guys to be studying them here at Grand Canyon?

Houston: So yeah, good question. Kaibab squirrels are one of six subspecies of tassel eared squirrels. Tassel eared squirrels are found from here in Arizona into New Mexico, Colorado, Utah and even down into Mexico. I believe two of the subspecies are in Mexico. The largest range subspecies is the Abert squirrel. And they're what you'd be familiar with on the South Rim. They extend from the South Rim there into New Mexico, Utah and Colorado. There's another subspecies, lives the Rocky Mountain front, the Kaibab squirrel, our special squirrel here on the North Rim, endemic to the North Rim, have one and the smallest ranges of all the subspecies. So, they're very cute, cute squirrel, large white fluffy tail. And they're a fairly large squirrel as well compared to most other rodents you see around.

Juli: Can you explain what an endemic species is?

Houston: So yeah. An endemic species is a species that's just found in one geographic location, generally an isolated area. And more likely than not, they might have special traits that have allowed them to persist, and kind of evolve in place. So, it's really important for us to study these endemic species, because they can lend some of those special traits that we want to understand that helps them survive in the location they find themselves in.

Juli: For Kaibab squirrels, what are some of those traits that make them different from other Abert squirrels? And do you guys know how those traits benefit them here?

Houston: So, we know part of that answer at least. So, I mentioned there are six subspecies of this tassel eared squirrel. And they're all a little different. So mostly it's based on their pelage, which is kind of their fur coloration and patterns. So, Kaibab squirrels will have a fully white tail. That's one of the bigger differences. Whereas an Abert squirrel will have kind of a white and black, kind of black underneath. And it's a little more speckled I guess, overall. So, our Kaibab squirrels in the right light just looks like a bunch of snow or something. Their very white tail, very easy to spot on the landscape, that sort of thing. They also have, more often than not, black bellies compared to Abert squirrels that have more white bellies. Although there are actual, there have been some sightings, where that's actually reversed, but it's fairly uncommon. They believe that that change has occurred just because of one gene mutation. So Abert squirrels and Kaibab squirrels and arguably all the other subspecies used to be a little more connected through Ponderosa, and other pine forests that used to be a little more connected. And after long periods of time, some of those pine forest pockets became a little more isolated. And that's how our Kaibab squirrels have found themselves more or less stuck here on an island on the Kaibab Plateau.

Juli: So, you said that they're really easy to see because of their white, fluffy tail. But a lot of times visitors are asking, how can they see one? Where can they see one? How rare are they? How many? Do you have any answers to those questions? Any tips for how visitors might have the best chance of seeing a Kaibab squirrel, and what should they do if they see one?

Houston: Sure. So, I could go into some history of population, because it's tough. They're, they're kind of a cryptic species arguably, just because they're very quiet. They escape predators by climbing a tree and just going silent. And they're not active throughout the day. I mean, they will be, they'll bounce around, but you just kind of have to catch them at the right time. And you have to be in the right area. So, you need to be one, in pine forests, although even in our mixed conifer, you can run across them here on the North Rim. But they are pine obligates. So normally they're around, on the North Rim here, mainly ponderosa pine. Other areas they'll eat on other pine trees like pinyon, etcetera. So, part of the difficulty in seeing one now is there's just not that many, it seems. But population has always been difficult to determine. There's been biologists working on this for almost a hundred years, and population estimates vary wildly. So back in, like the 1920s, they thought maybe 5 to 10,000 of them were in existence by the 40s, maybe 3000. By around the 70s, maybe one biologist thought 1000, another thought 5 to 10,000. And even more recently, like in the late 80s, something like 22,000 squirrels was the estimate.

Juli: Wow, is that all Kaibab squirrels?

Houston: Just Kaibab squirrels. So, we've been doing some surveys that have been done historically to try to figure out how many we have. They call it a feed index. So basically, we would set up a grid, a fairly large grid, and you'd go 5 or 10 meters and count how much feed sign you found, and that'd be feed that's dropped from the tree as their feeding. It could be where they're digging up mushrooms, a number of other things as well. So, you'd count how many of those little meters had feed sign and you'd continue doing that throughout the grid. It takes a couple hours to do this, this survey. And then you'd kind of do some math to say, well, how many of those plots out of about 270 had feed, which then you could say over time is feed increasing or decreasing? And they would kind of try to extrapolate that on a landscape level to try to figure out how many squirrels we have. So not simple and I would argue pretty unreliable. So, the last decade or more, we've been doing those feed index grids, and we would just start getting zero feed sign. And we know the squirrels are around, but it's hard to extrapolate how many squirrels you have when all your grids say zero. So, we do know they've been in decline for over a decade. Maybe a fairly stark decline, having worked with the feed index grids. And we have a new kind of novel protocol here for searching for squirrels on the Grand Canyon, I might only speculate several hundred, maybe a thousand squirrels currently on the Kaibab Plateau. Again, it's kind of difficult to put a good number to it, but that's why we're working on it. So, to find the squirrel, if you want to go out and see one, you're probably going to need to hike some miles, maybe go for some drives and you're just actually going to have to get lucky. You could also go where previous people have spotted squirrels. That can be a little more reliable. Last year, for example, we had a pair in the North Rim Campground, so they were just really visible. But even then, you kind of had to get lucky. So, if you find a Kaibab squirrel, we would like to know about it. Because they're so rare currently, we take all sightings from the public and staff. We do our new survey protocol to look for feed sign. And we're building a map of where these squirrels may be. And we're then looking into why are they in the places they are? We're trying to get trends. Are they increasing? Decreasing still? Luckily, I do feel like in the last two years or so, they have been, in fact, increasing just slowly. This fall actually, some anecdotal evidence from the forest suggests maybe they’re rebounding pretty quick, which is definitely possible. They can have 2 or 3 litters a year, and each litter can have 3 to 5 squirrels in it. So, they can proliferate pretty quickly. That said, they're also pretty low on the food chain and they make a tasty snack for a wide number of predators. Historically, goshawks were considered one of their primary predators. With boom and busts of populations we don't seem to have many goshawks around right now either which allows, perhaps, for a quicker rebound. I was mentioning a feed index grid. That's been the historic method for surveying for these squirrels. Our kind of new, more novel method is really just go find the squirrels. So, we just go on hikes looking for a winter feed sign, where we document that. And then we'll actually if we find some feed trees, we will then circle around to try to map out their winter territory, which could be almost 20 acres in size. Having kind of worked through this process, we've also learned that those feed index grids are somewhat biased. You could have a historic grid just that happens to be on, say, a historic winter territory, and so maybe you're just catching sign from one territory year after year and you're not actually getting the bigger picture. And the fluctuation in sign quantity could be more of a factor of how much feed is on the landscape that year. So, maybe I should back up one more moment. These Kaibab squirrels and just tasseled squirrels in general, are the only squirrel species that's really active year-round. So, most squirrels kind of cache food and kind of hibernate some in the winter. These squirrels do not. They don't cache food, and they therefore also have to stay active all winter. They do not hibernate. So when they start getting really hungry, late in winter, really all they're eating is the inner bark of trees. So at the end of a twig, they'll lop off the little pine needle palm, that'll fall to the ground, and then they'll kind of take off the end of that twig and corncob it. So they're like stripping the bark and eating the phloem, the living sugary part of the tree. And then they'll drop that to the ground. So, we're looking for those little pencilized twigs. It's a telltale sign of a tassel eared squirrel or Kaibab squirrel. So we're looking for that type of sign to figure out where they were in the winter. And then based on that, you have actually a better chance of seeing them in those areas as well. They'll generally only be within about a square mile of their winter territory during summer. Their summer territory is quite a bit longer. And of course, they do other things too. They can disperse over long distances, although we don't have a good bearing on how far that might be. But based on the winter territories we have observed, some of those can have miles between them. And I guess in nature sex is a good driver for dispersal, so they're often most likely just trying to go find a mate when they're out dispersing. So that's our current approach is more or less just let's go find the squirrels and figure out what's going on. But we are looking into some other, novel approaches, some of which have been pulled from mesocarnivore models. So, we're trying to collect DNA, using attractant stations, offer up some bait, and hopefully they come and leave some hair behind. We're trying acoustics, a noninvasive methodology that's becoming fairly popular for a number of species. Even though they're pretty quiet, we're hopeful some of that will still be fruitful. So, yeah, we'll put up a recorder kind of in a center of a winter territory where we have a higher expectance to see if squirrels will be there. We have a couple months worth of audio that hopefully will pick up a squirrel sound. They're pretty quiet, though, and they don't talk a lot. And their audio doesn't really project that far either. So, we'll see how it goes. We're also trying some track pans. So, we make this little, square or triangle kind of a rain proof tunnel, that they can walk through. And the bottom of that has a metal pan with kind of like chalk or ink toner, something that really can leave nice footprints behind. And then we can collect those footprints to see presence or absence of squirrels. A lot of these methods don't tell you how many squirrels we have, but it might move us in the right direction. So this is all been experimental in 2024, and we have yet to get some data on it. Additionally, we're trying to collect some actual, genetic samples just from tissue of squirrels that are recovered from being hit by cars. We put a word out with Arizona game and fish to collect samples from hunters because they are actually a hunted species, believe it or not, despite their low numbers. The goal is to get genetic markers, so that we can do eDNA. So, Edna is environmental DNA. Historically, it's mainly been done in water bodies. So to back up half a moment, we're all shedding skin cells. So are the squirrels or the birds. Just everything is. And so, you can filter water in a pond, you can collect those skin cells that have come from everywhere. And then you can actually determine what is there, based on kind of a genetic library that we pull from. Science keeps progressing. Not long ago, someone demonstrated for the first time that you can actually sample spider webs for the same purpose. So, these spider webs are sticky. The skin cells stick to that, and we can see what's around. So that was one of the first terrestrial uses of Edna. But going forward, we think we'll be able to perhaps filter air to determine presence absence of these squirrels and other species really. It doesn't tell you an abundance, just a presence or an absence. So that's kind of an exciting way to go as well.

Juli: Yeah. That's cool. It's kind of gross to think about, but kind of cool to think about, too.

Houston: And it's great because it's also noninvasive. A lot of studies of wildlife requires getting your hands on or playing a call so that they call back and it's kind of invasive. It can alter their behavior, change what they're doing. It can even add stress depending on what you're doing. So yeah, the noninvasive methods are preferred. Hopefully they work.

Juli: Hopefully. So, you've said that the Kaibab squirrels are pretty quiet. But other than that, is there any ways that you could think to describe the personality of the squirrels, the ways they act, or your interactions with them? Anything memorable?

Houston: Yeah. Well, so squirrels are squirrels. They are cute, of course. Especially when they're, like, chasing each other, which more likely than not, it's when they're rutting and they're not actually playing. I don't know how much play they have, and they might play more when they're tiny tiny. And that's pretty darn cute, too. I mean, two cute squirrels chasing each other. It's hard to beat that. When they have their new litter, those are especially cute to watch too. Younger species in general, including our cute Kaibab squirrels, of course they're cuter because they're young, but they're also more fumbly. They'll like, try to jump to a branch and kind of fumble around and, and they're a little awkward. And that just adds to the fun. A month or two ago as well, I was out on, on the rim and I actually flushed a peregrine falcon from the cliffs that started calling some. I listened back and actually could hear a Kaibab squirrel make three short little calls. And so, since we've been into the acoustic realm of late, it gave me hope that maybe this, this type of survey and acoustic survey could work. I'm still a little skeptical, though, because it's just not that loud. It does take a trained ear to pick out a Kaibab squirrel from the forest. But their call is very much unique compared to other species. Probably the squirrel that most people are familiar with is the southwestern red squirrel. They're really territorial. They'll yell at you; they’ll chat at you. They make sure you know they're there. They're kind of like the alarm calls of the forest. Where comparatively, these Kaibab squirrels are really quiet. You could walk right by one, and they might not say anything. On occasion when you approach, they might let you know they're there. But generally, they're just a silent species. They're pretty nonchalant. They don't seem to be that worried about predators. They'll just kind of go about their business looking around and just being squirrels. That also means they get snatched up I think, pretty easy. And their white tail probably doesn't help with that too much. The white tail could have a number of purposes as well. It could be this big white flag saying, grab me, grab me where the rest of the squirrel is dark. So if a hawk comes and tries to snatch it, it might try to grab the white fluffy tail. And it's so darn fluffy they're just going to miss. And then the squirrel gets away. It's also nice and fluffy to help with cold winter temperatures. In the winter, they do sleep even though they're active year-round. They'll actually kind of ball up with their tail on their face, kind of in a nice little round circle to help stay warm. So that really fluffy tail really helps kind of hold some of that air stable to add that warmth that they will absolutely need when it's really cold out. So because they are so nonchalant, not too worried about predators around, they're not very good with cars. They'll, they'll just kind of wander out in front of the road.

Juli: I’ve noticed that.

Houston: Yeah, we have a pretty high squirrel vehicle mortality wherever, wherever you find them. So it can be a good chance to see one. But at the same rate, speeding, even going at regular speed, sometimes it's hard to avoid them. So even though I'm describing them as kind of nonchalant, carefree, they are actually fairly observant. So if you see a squirrel in the woods, they might see you looking at them. And part of it is humans have this predator look. We're on our hind legs, our claws, our front claws are free. Our eyes are in front of our head. These are all, like, telltale predator signs. And they'll, they'll notice that. So often if you see one and they see you, they're going to be like, huh. And they're going to start probably walking away from you. And if you follow them a little, they'll be like, oh, this, this doesn't seem right. And they'll pretty quickly climb a tree. And at which point they try to go to almost the very top where they just then go silent and then they wait for the predator to leave.

Juli: Is there a reason, I feel like usually when I've seen them, they're running across the ground instead of climbing up a tree, until eventually, like you said. Is that just when I see them? Are they normally running across the ground? Is there a reason that they like, hang out more there than up in the trees?

Houston: So, they probably hang out more in the trees than you think.

Juli: Oh, I'm just not looking up, probably.

Houston: Yeah. And they're hard to see, like, there's a lot of branches in a tree. They're just hard to see up there. Especially because they just go completely still. They're not, like, flailing their tail back and forth. They're just up there quiet. And really being on the ground is when they're the most vulnerable to predators. The trees offer a lot of protection. So they nest in trees. They make the most of their living in trees. But a lot of their living has to be done on the ground, too. So certain times a year, they're certainly eating that inner bark, so in winter, primarily. In spring, they're eating baby pinecones. And throughout the summer season, a lot of pine cones as they mature. And then a big portion of their diet is actually fungus on the ground. So mushrooms, primarily. It's where they get a significant source of their protein, and it's just a huge part of their diet. So that's, they're on the ground to go find and dig for truffles essentially. So that's probably when you're seeing them. Sometimes they're getting from tree to tree that way as well. But if the trees are in a close enough proximity, they can actually, like little squirrel ninjas, jump from tree to tree to tree and never really need to come to the ground.

Juli: So can you elaborate at all on how they have a symbiotic relationship with the forest, or to what degree they have a symbiotic relationship with the forest?

Houston: Absolutely. And they absolutely do. They are pine tree obligates, and you could argue the other way around, almost. So it's a symbiotic between, a symbiotic relationship between squirrels, the trees and the fungus. There's been a number of studies over the last decade or more that have shown how interconnected the forest is through mycorrhizae networks. So the connection of all the different fungus in the ground helps give nutrients to the trees, and the trees will actually give nutrients to other trees. And they kind of even can communicate through the ground. So it's this very interconnected network. So the squirrels will actually eat some of that fungus and spread the spores of that fungus, which helps the health of the soil and the trees. And then the trees are also feeding the squirrels with their, the inner bark and their pinecones. So very much a connected circle there with those three. They're also kind of on the lower level of the food chain. So, they're also then supporting other critters in the forest by providing themselves as prey, especially to say, goshawks and other predators and scavengers.

Juli: Do you think the way they have this relationship with the forest, that changes that you guys see in the squirrel population or where they are, can tell you things about changes in the forest or vice versa? Or is there anything else that you think would be beneficial from studying this population?

Houston: Yes, absolutely. And I think a lot of those questions are still arguably a ways off from being figured out. There have been a number of studies on the lives of these squirrels and how they make a living. But there's so many unknowns as well. The more we learn about any species, the more questions we have. So our number one goal currently at Grand Canyon is just to figure out how many squirrels do we have and where are they. Then we can start asking the questions of trends, habitat assessments. So we're also looking at why the population fluctuates, and we do not have a good bearing on that in the hundred years that we've been studying them. There's a number of hypotheses out there. And I could go through several of them here. One of which is a predator prey model I kind of alluded to earlier. So when you have lots of squirrels, you're probably going to have lots of critters eating them. So if we're looking at goshawks, which might be one of their primary predators, when you have high population of squirrels, you have a lot of goshawks, but then maybe there's getting to be too many goshawks and they're all hungry. And so they're starting to eat the squirrels faster than they can reproduce. And you could have a pretty big crash in the population because of that. So that's one leading theory. Drought and climate change also could very much have an impact on these squirrels. With long periods of drought, you might have trees that are more stressed and they're not producing as much of that inner bark that the squirrels are eating and maybe fewer pinecones as well. So that could certainly create a food scarcity for these squirrels. I've been hypothesizing, there's been some literature that shows that some plants are creating more tannins, kind of related to stress, but that has been tied directly to increases of CO2. Yeah, climate change is really interesting because it is impacting the landscape in so many different ways, in so many different areas. And this is especially important to research, because I understand the southwest may be hit exceptionally hard by some of projected climate change impacts, mostly related to heat and drought. So, with increases of CO2, they have shown in a variety of plants that these plants will actually produce more tannins. Some of that could be stress related. And you might get a similar result from drought. But with more tannins, the food becomes less nutritious and less appealing or less available overall. So, this has only been shown in a number of plant species. We have never in the scientific community, to my knowledge, looked at an increase of tannin production in Ponderosa itself. It has been shown in a number of other woody plant types. So we're wanting to pursue that avenue eventually. We just have so many questions to answer. But especially with climate being one of the big key issues of the day, it could be an avenue we go down. Drought could very much be a similar cause in an increase of tannin production, and therefore the food becomes less nutritious. With fewer nutrients and sugars in that food source, the squirrels just might not be reaching their calorie balance. For a lot of wildlife species, it's calories in, calories out equals survival as a way to boil it down. The literature has largely ruled out disease as one of the reasons for these big population crashes. But having been talking with our veterinarians recently, we believe there is reason to revisit some disease models, especially plague. It’s a cryptic disease that's hard to detect. And because these squirrels are at the bottom of the food chain, it's hard for us to get reliable samples really quickly, they just get snatched up by ravens and goshawks and other scavengers. So just because we haven't detected it yet doesn't mean that it's not there. And we do know Grand Canyon has plague. We have plague on both rims. Science has progressed and we do have more tests to determine if plague has been on the landscape previously because the survivors of plague will actually have essentially antibodies that help them survive that last epidemic. So we're going to hopefully be moving in that direction in the coming years to see if we can detect that as well. So kind of related to their population estimates. It's been a controversial subject whether or not this squirrel should be a hunted species. So of course, there is no hunting allowed within Grand Canyon National Park boundaries, but they are currently a hunted species on the forest. Over time, that's gotten a lot of pushback as well. So even back in the late 1800s, President Harrison and Roosevelt created the Grand Canyon Forest Reserve. That protection continued through, around the late 1930s with the Forest Service. By 1965, actually, the Kaibab Squirrel National Natural Landmark was established. Usually, National Natural Landmarks are designated for educational purposes or, sometimes cultural purposes. So it's not all that common for a species to be afforded a National Natural Landmark. But because they are so iconic with their bright white tails, I think that's part of the reason why they got that designation, which helps continue protection for them. So I was mentioning earlier, I was throwing out some numbers for how many squirrels we think exist. So as early as the 20s there's like 5 or 10,000 squirrels. But at the same time, a lot of people were concerned that there weren't that many squirrels around. So they got some biologists on the job, and they thought, well, you know, they're actually probably doing okay. By the 1960s, some newspapers and magazines really started to look at these squirrels, especially because the state was starting to talk about rescinding protection from hunting. So there was actually large public outcry in around 1964 to say, no, why would you hunt this squirrel? There's not even that many around. Like, what are we doing? So the state said, okay, we won't do it this year. And it actually potentially corresponded with a year of low turkey numbers. So they said, well, we'll just call off the turkey hunt and also call off the squirrel hunt. By 1965, though, pretty much the same year they created that Kaibab Squirrel National Natural Landmark, hunting became legal for these squirrels. And because it wasn't being publicized as much that following year, there wasn't as much public pushback and the squirrels became huntable. And that's remained the case ever since. That said, there has been occasional outcry, found some literature that showed in the early 70s and actually arguably currently now, there has been some pushback from the public, in part because those corresponded with years of pretty low squirrel numbers. So it starts to feel weird when you're still hunting a species, when you can't find any. But since we don't quite know their population dynamics, the causes for their booms and busts, that has been reason for us to have that concern. But it is also shown that maybe these squirrels are actually a little more resilient than we think. But again, we want to get a good handle on it before we let things go too far in either direction. So also in the early 70s, biologists were concerned about their population numbers. So they actually did a translocation of some Kaibab squirrels. So there actually is now an additional population of these squirrels. They're out kind of near Mount Logan or the Trumbull Wilderness. So that would be kind of, Western Grand Canyon still on the north side of the river, but kind of on the northwest corner of the park.

Juli: Is that a common thing to take an endemic species and put them somewhere else?

Houston: Fish and Wildlife Service has translocated or transplanted a number of species, especially when populations are low, to kind of hedge our bets. So if one population fails, hopefully that other population may persist. And they do that for a lot of terrestrial species, number of fish species can be moved to avoid predation or hybridization. Just depends on the species. But it is a semi common approach to, it's really to hedge our bets. So that's what they did then. And you can still find Kaibab squirrels out in that country as well. So these squirrels can live, it's estimated 3 to 4 years in the wild. In a zoo, the longest recorded has been about nine years. They're having, I think I mentioned, like, three litters a year. Just depends on the year. And some year they may only have one litter just depending on the food resources available. But they have to reproduce quickly because they're gobbled up so quickly too. They are pretty low on the food chain. Some estimates show like a 50% mortality rate. So they have to breed fairly quickly to keep up with that. And that's also why your population could have these big swings. You can crash pretty quick if everyone's getting eaten, but luckily, they can reproduce fairly quickly to make up for it when times are good.

Juli: I was curious of when they have a litter like what that survival rate is, and if it's mostly because of predation, the ones that don't make it? And also, are there any in zoos right now?

Houston: I'm unaware of zoos that are advertising their Kaibab squirrels, but it's not to say they're not there. I'm sure there are tassel eared squirrel subspecies in zoos, and they're all pretty related so they'll have similar lifespans and similar habits in a lot of ways. So, yeah, survivability of young is probably more related to predation than not. And it's really about 50%. So about as high as an adult. So they do time their litters with the season. So usually, their first will be in spring, and May or June more often than not. Then they can have a mid-summer litter. And then I think we just had perhaps our last litter recently. There's been a lot of squirrel sightings this fall. So I'm hopeful they've actually had three litters this year. And some anecdotal evidence is showing we might have had that. So it might have been a pretty good year for a Kaibab squirrel.

Juli: Cool. Thanks, Houston.

Houston: Yeah, no thank you. Keep up the good work. We appreciate you educating the public and getting the word out. We all are in love with the squirrels here and we want to just make sure they're doing well.

Juli: The Behind the Scenery Podcast is brought to you by the interpretation team at Grand Canyon National Park. Special thanks to Houston Thompson for this episode. We gratefully acknowledge the Native peoples on whose ancestral homelands we gather, as well as the diverse and vibrant Native communities who make their home here today.