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The Past, Present, and Future of Wild Bison

The Nature Conservancy’s Chris Pague sat down with us at Bison Works 2018 to discuss the history of the Medano-Zapata herd, bison ecology, and the prospects for a future of wild bison.

Can you give us a brief overview of the history of bison as a species?

Bison were one of the primary ungulates in the country, and they occurred from Virginia to Florida to California to Mexico and into Canada and Alaska, and they were a primary influence on the ecology of North America, but we all know the tragic ending to that big population. The economy of the whole continent was changing over to a market economy from a subsistence economy. Of course, the entertainment of Americans and Europeans shooting from trains is well known, but the market hunting, in general, was a major factor. The population eventually went down to less than 1000 animals in the United States, and those animals that were left were rescued by a few ranchers, a few private individuals, and were protected in Yellowstone National Park. From those few come what we have today–half a million bison.

Pague looks on as a bison waits in the race to enter the squeeze.

Pague looks on as a bison waits in the race to enter the squeeze.

The history in between those two points is one in which the Bronx Zoo and the Wildlife Conservation Society played major roles. They saved many of the individual bison, brought them together and bred them, created the American Bison Society in 1905 with familiar names like Teddy Roosevelt and William Hornaday, and then released them into appropriate places to help restore populations. What we see today are patchy populations in publicly-owned lands, a few ranching operations here and there, and a few big ranching operations, but most of the bison are now part of the livestock industry, raised for their meat. This is not wrong, in fact is necessary, but is meant to point out that wild or conservation bison are a small part of the current bison numbers in North America. However, the bison is a well-known animal and a species that deserves to be considered more broadly than simply as livestock.

What were some of the ecological effects of removing such a huge population of keystone grazers from the land?

Bison, like so many other widespread animals, probably had different life histories in many of these places; the forest of Virginia or North Carolina would have been different from the sagebrush country to the West. But where they were most abundant, in the prairies and grasslands, or even in the valley bottoms of the forested regions, they had a major influence. They were the primary herbivore and would have consumed large quantities of the grasses and forbs when they were there. We don’t really know a lot about the vast numbers–30 million or more bison–whether they migrated every year or many years or under what conditions, but the point is that they did move in large numbers sometimes, and when they did, they had to eat all the way. And that made a big difference to the vegetation they passed through.

Another thing about bison that was amazing in those times–when there were droughts, the bison moved. They didn’t just move from winter and summer. People like to think that, but when it got too dry and the grass didn’t grow and you’ve got some several thousand bison in a population, they’ve got to move. If they saw a thunderstorm in the distance they would take off towards thunderstorms.

So they had that big difference on the ground. Mountain Plovers and many bird species liked to breed where bison had an influence–they still do, whether it’s cattle or bison. Bison loved to graze on prairie dog towns because of that fresh grass, and it’s the same with many ungulates–fresh growing grass is just a prime attractor. And there are some birds that depended on them. What we call the cowbird today has a name that makes no sense historically and should not be called the cowbird — it’s really the bison bird.

I think the other part that a lot of people really don’t understand is that bison are an ecological disturbance. So the term “keystone”–scientists will fight over what it is–but bison had a major influence where they occurred in large numbers, and they impacted a lot of species around them. And, for predators, following them and occasionally picking off the calves, claiming the dead animals as they were, the lame animals, they provided a huge food source for the key predators, and we also can’t forget the scavengers, which, we don’t have a lot of those left, but they were probably superabundant when bison were in the millions.

How did the Nature Conservancy get involved with the Zapata? What are your goals for the property?

Hisa Ota, the former owner, started the bison operation in the San Luis Valley here, and he really fell in love with the bison, and so it was a little bit of a challenge for him to consider the bison exclusively as an income-making tool. And that was kind of an interesting situation. We had a lot of conversations before we acquired the ranch about bison and what his dreams were about the bison, what he hoped we would do as well, and it basically meant that he loved the bison as a species. And he knew that to keep the population under control, harvest was something that would have to be done, but he cared about bison being bison.

As an ecologist, that was of great interest to me, and so we did a study across the entire region–the southern Rocky Mountains–that found that this landscape, this corner of the San Luis Valley, with all the public lands and the big ranches, was the best place, the most suitable place, to establish a conservation herd of bison. And so one of our goals was, of course, to create a conservation herd and then to try to influence the public lands around us to try to see who would embrace that idea of the restoration of bison. It was to be the only conservation herd of bison in the southern Rocky Mountains.

When we took over we asked what does that mean: conservation herd? Because a lot of people will claim “conservation,” and we don’t want to denigrate anything they’re saying, but at the same time, we’re a science-based organization and we wanted criteria. And the primary one was to make the genetics as good as we can. Another was that we wanted there to be selection within the herd because it’s a large enough herd. We want males to be fighting for their females and not just as a production herd keeping it 7-10% males because we know they can service all the females. We want some of the animals to live a long time. In the wild, in the Yellowstone herd, we have good population data on how long animals live, so we wanted to see that, especially with the females, being matriarchal animals, that the females have a huge influence on how the herd behaves and how they pass it on. We wanted to respect the population dynamics of the family unit because that’s really important in bison. The calves stay with their mom around three years.

So those are some of the basic things, but the biggest one for us was: rather than deciding what we wanted bison to do, we want bison to decide what they want to do. Our job then is to keep those other parameters, keep the population size within some reasonable limits for the carrying capacity of the ranch, so that the ecological conditions are good. So that meant that we decided to take all the interior fences down. Let’s let the bison choose whether they want to go that way — or that way.

Would the other option have been rotating them around through the pastures?

You can do that, but that’s our choice, right? We’re all of a sudden telling bison what to do as though we know. One day on the ranch I was sitting on top of where the corrals are, and I was looking off way in the distance to the northeast when I saw a cloud of dust. And I pulled my binoculars up on it, and it turned out it was, I’d guess, about 60 to 75 bison just running, full speed, just running. And I watched them for a little bit, then put my binoculars down and went back to whatever I was doing there, and came back a little while later, and they’d moved a bit but they were still running. Just to make a long story short, for about 25 minutes they were running at a gallop. There’s nothing chasing them–I mean what’s going to chase them, a coyote’s going to chase them that far? No. So, I don’t know why they were running, but the fact is, they never had to hit a fence. They didn’t have to stop. And for whatever reason they were running, they could do it. And I didn’t know any other place where they could do that. So what are bison? Bison are whatever bison are supposed to be and that’s wonderful. I know it’s frustrating to managers sometimes to not have that option of moving them to wherever we want to move them, but that presupposes that bison aren’t doing the right thing, and that’s a hard judgment for me.

It’s an interesting balance for managers to figure out how to let bison be bison when a lot of other aspects of the ecosystem are not the same. For example, there are no predators, so how do you strike the balance of letting the bison be bison on a very different landscape?

Yeah, and I mean clearly they’re protected. They’re in a 45,000-acre pasture, there’s an exterior fence, and the predators are not there like they used to be. So I feel comfortable with the decision–I mean I would love to see some of the predators back too, of course, I’d love to see that interaction–but we’d have to think of it too in the context of 1600 bison. Then we’d be controlling–and we do control that part of the bison, we don’t let them build up too far to starve to death and all that, so, we’re doing the best that we can, but the indicators are that bison behavior is what we think bison should be doing, and the effect on the landscape is what the bison decide to do, except within the limits of–we’re not going to mess it up, you know.

And I think this year was a good example of that. We had a really dry start to the summer here, so I called Duke to ask, what’s your contingency plan here? He told me the contingency plan in general for all of the animals that he works with, but what I was really after was is: I know I’ve put you in a bind by giving you one pasture because you can’t box them in and say no you can’t graze here, we’ll put you over there in three months or whatever, but, we’ve got a drought. And we can’t control that factor, the only control we have is over the number of bison. But the one pasture and the timing with the calves out there at that particular time of year puts them in jeopardy. So this year we’re going to talk about–given the climate change we’re all seeing — the predictions of the future, is there a different thing we have to think about? Is the base number of animals too high? We always have too few animals, and I know that impacts the economics, but we’ve got to have a conversation about that and we’ll see where it leads. I want to seriously talk and Duke’s always great about that: let’s find a solution to whatever the problem is.

You mentioned that this area of Colorado was the ideal place to establish a conservation bison herd. What’s the history of bison in this area?

When the Spanish first came into the Valley their first observations as mentioned in the records of Don Diego de Vargas in 1694, they recorded several hundred “shaggy cows.” And Native Americans were hunting them at the time. So Native Americans tried to show them how to hunt them, but apparently, the native people who had used the San Luis Valley for bison hunting were better hunters and horsemen than the Spanish with their armor and burdened horses. After that, the Spanish tried to take a bunch of them home to the Governor. It wasn’t a good move. We know that bison don’t really like horses very well, so that was a disaster.

But interestingly, there’s not a lot of observations of bison in the Valley after that. A few remarks by Mexican observers and then almost none. So that’s a big mystery because we know South Park, just a few miles north of here, is where the last bison in Colorado was killed in 1898. They lasted a long time over there, so there’s no reason that this wouldn’t have been bison country.

So we do have a gap to explain there, but we know historically and of course, prehistorically there’s huge evidence of the previous species of bison, Bison antiqua, in this area. So we know that bison were here, but we don’t know a lot about their ecology. Some people summarize that by saying, “Oh, bison only visited the Valley. They came over here from the Great Plains, they migrated and then left for a while.” Maybe, and this has to be a hypothesis. My preferred alternative is: there’s a building case for the fact that when the Spanish and then later the rest of the Europeans brought cattle diseases to the San Luis Valley, they had a major effect on bison. There’s pretty good evidence for that in a lot of places. I suspect that’s more likely what happened: the Spanish brought their cattle and everything else and the cattle diseases came and they really reduced populations. That’s probably why later observers only saw a few. This is an alternative idea.

But, there are of course alternative explanations for that, and some of my colleagues would prefer that it be that they moved in and out. We have here in the San Luis Valley extremely cold but dry weather, great forage, lots of water that rarely freezes, and very little snow for the most part. That’s prime bison habitat. I suspect that bison lived here, their populations were greatly reduced by diseases and were finished off by the explorers and miners and the military. We know that when Kit Carson was at Fort Garland, the native animals were reduced such that he asked for food for the native people from Congress.

So that’s the history of it, and there have been only a few captive bison herds in the Valley since. There are a few records of bison recorded in the San Luis Valley in publications of the Denver Museum of Nature and Science, including at least one skull and that’s it. So we’re kind of making it up based on the best available evidence and drawing the conclusion based on actual observations and ecology. It is not conclusive but reasoned.

What are some of the scientific aspects of what you and the Nature Conservancy are trying to do here? The DNA testing, for example?

After the American Bison Society re-formed, not too long ago, and we had meetings where we said: well everyone who has bison can contribute to bison conservation in different ways. It’s not that you have to have a pure Yellowstone herd or you have to have the purity ecologically correct, and so forth, but that everybody can make some contributions, and we will put some criteria out there that say: how can you do better? So if you chose to do better, to improve the conservation message, how could you do it? So we proposed criteria with ecoregional planning, saying that this landscape would be a highly suitable area for bison, especially with large public and private holdings. You have almost 400,000 acres of potential bison habitat here on public land and The Nature Conservancy’s land.

What we decided to do, we could work on criteria such as sex ratios, freedom to roam, no feeding of artificial vegetation from the area–the hay we harvest is from the ranch, and we only feed them that way one roundup a year. But the one thing we knew was a problem was that we had tested the genetics and the long history of cattle mixing showed up here, and we had something like I think seven different origins of this herd, which means we did get some animals that did have some DNA from cattle. Nobody bred the cattle here, it came from long ago. And so that was one thing we figured out that we could really do. Because we were letting the bison be bison–you can’t do more than that, they’re going to be what they are. We got them enough room to roam, if they want to run, the males can fight, the females can divide up into bands, it’s not all just one herd, so the behavioral stuff I thought we did a pretty good job with. So what was left was: what could we do with the genetics?

A lot of people debate about the genetics, but the one paper that influenced me showed that there’s evidence that mitochondrial DNA of cattle that exist in female bison can negative impacts such as lower weight, less stamina, and perhaps calves of lower weights–all of which are known to be, in livestock business, factors that you would rather not have. So that’s why we’re working on the DNA. Since mitochondrial DNA is only passed through the females, we take tail samples from female calves, we send them to Texas A&M, and they send us back the information. So as long as we can identify the individuals who have that mitochondrial DNA with cattle markers, we actually remove that female from the herd the next year at roundup so she never breeds again. But that means we still have to identify any calves she had. We’ve got to wait another whole year. There’s no instant response, which is a shame because if we could just detect those calves with bovine genes right away, we could remove potentially bad DNA quickly.

The other thing we’re doing, and a lot this is with the National Park Service and the USGS, is studying the grazing ecology. We’ve got an overpopulation of elk, but since we can control bison more than we can apparently control elk in the context of land use, there’s a lot of eyes on us to work on the bison side of it. What we’re interested in is: are the bison and the elk eating the same things or different things? We have found out in numerous cases through the work of biologists from the USGS and led by Kate Schoenecker and Linda Ziggenfuss is that bison actually don’t really care for elk to be that close–they chase them away–so there is a little patchiness that’s created just as a result of that social behavior. And the elk eat more of the willows than the bison do. The bison eat the grass, and the bison don’t really like the wetlands quite as much as cattle do, so we get a little difference there. Additional studies are underway.

In what I’ve read about bison conservation, there are different opinions about whether to keep the herd closed or not. Are there advantages or disadvantages to keeping a herd genetically closed like it is here?

We looked at that. When we did the genetic testing, we weren’t just looking for the markers for cattle. We were also asking how much heterozygosity do we have in this herd, and this one and the one at the Tallgrass Prairie are two of the most diverse–heterozygous–herds in North America. So as long as you have a reasonable number of males and a sufficient population size, you can maintain that. The size we have is estimated by the geneticists to be sufficient to maintain that genetic diversity, so we don’t have to bring anybody in to bolster our herd as they did with the Texas herd–they weren’t even getting successful reproduction. Ted Turner gave them some new bison bulls from his herd of Yellowstone genetic origin, and now they’re just reproducing like crazy. So we’re not in that shape, but we do monitor it. And all of our herds, in fact, in the Nature Conservancy, are monitoring the heterozygosity.

But the current home of the bison, the Medano side of the ranch, has been sold to the Great Sand Dunes National Park hasn’t it?

Well, we helped create the National Park. We helped design the boundaries for the Park, and the boundary goes down Lane 6. So that means everything on the north side of the highway, ultimately, will go into the National Park Service. The NPS will take great care of the natural, hydrological, and cultural values for the people.

I read the Environmental Impact Statement published recently by the Park, and they laid out several alternatives to possible courses of action with the bison, their main concern being the overpopulation of elk and their effects on the wetland areas. Their preferred option was adjusting the density of bison to .001-.01 bison per acre, which by my calculations, would only be about 50 to a couple hundred bison, obviously a huge reduction from where it is now. What are your thoughts on what lies ahead for this bison herd and the National Park?

Well, those are the great questions we’ve asked ourselves at The Nature Conservancy, and we commented on the Environmental Impact Statement. So basically, all of the local land managers, especially the NPS have a bit of a problem with the large elk numbers, and we are all working to solve it. Controlling elk numbers in the context of the existing policy is a real challenge. Bison, on the other hand, are more easily controlled. We are all waiting for the decisions on the EIS. The means of controlling overabundant wildlife populations on NPS lands are limited. In our comments, we wrote that we think that the size of the bison population that they’re calling for is too small, that you won’t get the free-ranging bison in the way that bison naturally behave. To manage such small numbers of bison over the long term, there would need to be ways of managing genetics such as translocating animals from other populations. Technologically this is feasible. It goes back to one of TNC’s major decisions on the herd — we chose to have bison be less limited and more able to behave in ways that bison naturally behave in a wilder situation.

Another consideration is the degree to which bison would actually be observed by visitors. Even the 45,000 acres in which they occur today is extremely large for 80 bison and would often be invisible to visitors. The NPS has multiple factors to consider and this is another one. The National Park Service has a preference for having bison on the land in the Great Sand Dunes National Park and Preserve. That is a big leap for the conservation of bison in Colorado and the Southern Rocky Mountains. Our studies and reports identify the landscape around the Great Sand Dunes as a very unusual opportunity for bison conservation. The resources are there. It is historically appropriate. And there is a genuine need for restoration of bison populations throughout many parts of their historical range. This is the challenge presented for conservation and the public land managers of the region.

What do you think about the dynamics between bison and other ungulates such as elk and pronghorn?

What our evidence suggests, working with Kate Schoenecker as the primary person on this, is that there is adequate forage to support the number of animals that are out there now, but over time, the vegetation will be degrading. The bison are restricted to ~45,000 acres with a lot of wetlands. The vegetation that follows grazing events is a very high quality for the other wildlife of the area. The elk are naturally attracted to the area. With few natural predators and limited predation by people, the fact is that we need to reduce the herbivore population in this landscape to balance it out better. Right now the bison are a relatively easy strategy for reducing offtake of the vegetation. But the ultimate issue is reducing the elk population.

What’s the difference between wild bison and bison raised and treated like livestock in terms of their behavior and effect on the landscape?

We established most of our goals roughly based on information from Yellowstone. The Yellowstone herd of bison is no longer managed in the national park. There is also extensive research on the herd. It is also exposed to the full suite of native predators.

We also gained a lot of insights from the management of other herds owned by The Nature Conservancy. For example, the Tallgrass Prairie Preserve (in Oklahoma), which has even more bison than here, is a wonderful template for trying to emulate bison grazing behavior. The tallgrass is highly productive. They keep a smaller percentage of males, less than a wild herd, they manage the genetic health of the herd, and they do a great job. A big difference is the use of fire ecology and grazing with bison as a key to their management. Fire is the dominant natural process in tallgrass. So they don’t rotate with fences, they burn and the bison go to the burn, so that’s how they “rotate” their bison. So there are two models there–one of them is the Yellowstone herd and the bison can go mostly where they want to go. They graze and move with the forage and move longer distances when the snow gets too deep. Sometimes they move out of the park and there they are sometimes in conflict other landowners. When there were no wolves, the elk also caused the same kinds of problems as we see here. There was way too many elk, and they were all eating some of the same stuff. There was competition for forage and I would say degraded ecosystems in many ways. The reestablishment of predators has greatly altered wildlife behavior and therefore the impacts they have on the habitat. Bison behavior is, as far as we know, largely as it was centuries ago with the exception that one key predator is still not active in Yellowstone — humans.

So it’s a really interesting arrangement between Ranchlands and TNC. We have to adapt our goals, the ones TNC has for the herd, enough to make sure that the stewardship gets paid for. So we can’t get exactly what we want, because it’s not free — conservation actually costs money beyond land acquisition. Ranchlands challenges us with excellent questions about managing bison at such a large scale. They work hard to make adjustments that will benefit the long-term conservation.

Another element of bison conservation that Ranchlands has made great progress is that of education. Bison are a real attraction. At Virginia Zoological Park I was a keeper there for only three bison. But everybody came to see the bison! Bison present an attraction and give the opportunity to talk about ecology, economy, conservation, and a species for which there is a history. It’s even more impactful here with Zapata taking guests out to see bison where they can behave like bison — out there with the herd and can hear the grunting and see the mountains and the horizon.

The bottom line is, I think, if we’re going to maintain the connection with nature with bison behaving at least sort of like they used to, TNC has a responsibility to not just count the numbers and say we have bison, not just make sure its organic, not just make sure that the grassland looks good, but to have the bison behaving as they evolved as much as you can possibly contribute. That’s where I think we differ from some other bison herds. Yellowstone can let them do whatever they want, the wolves can eat them, a grizzly bear can attack them, all that. But even they have to manage them some. People are no longer predators except at the edges.

One of the biggest challenges: when we talk about conservation, it’s easy to talk about “sustainable grazing.” Well, we have to think deeper about what that really means. What are we sustaining? What do we mean by that? Have we considered the needs of all the wildlife? Are we doing the best we can? We can’t always fulfill our dreams or ecological goals, but I can look at bison as bison and I can go to many herds and I can look at them and I can tell you whether they’re behaving like the Yellowstone/Teton cluster because I know what they are doing up there and what their day-to-day looks like. It’s a heavier load and I think most ranch operators don’t have the time or resources to do it, but I think we owe it to ourselves, in our line of business especially, to pay attention, think about it, try to solve the problems, and if we really truly show the respect to those species like bison, and not just endangered species, we should give it a shot. Are we just providing a space that they happen to occupy or are we letting them fulfill their evolutionary and genetic history in today’s environment as best we can? That’s where I think we are today in our thinking. I don’t get to do everything I want to do here, you actually have to manage them. I just think about it. We act where we can. So it’s a test.


Fencing on the Medano

Fencing on the Medano, the pendulum swings. Most days, the rhythm of fencing makes for peaceful days of fixing and moving on.


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