Ask The Prairie Ecologist (Part 2)

Well, when I ask for questions, you deliver! This might have to become a more regular feature of this blog. I thought maybe I could answer all the questions in two posts, but it’s going to take at least three. And you’re welcome to keep sending in questions – I’m happy to answer them. I’ll do at least one more post to catch the ones that have come in so far, and then might start saving additional ones for down the road.

These questions are also helpful to me as I think about topics for future posts. Sometimes, it reminds me that it’s been a long time since I’ve written about a particular subject, other times, it’s just helpful to hear what’s on your mind so I can research and/or write about it when I get a chance. Thanks to everyone who has sent in questions so far.

Here are more questions and answers…

Steinar Karlsen asks:

You still have a lot of hair, Chris. Lucky you! ;-)

I’m wondering about prairie dogs. As I understand it they are very important for a prairie’s ecology.
So, what’s the current attitude to prairie dogs and how common are they typically?

Prairie dogs definitely create important habitat for many other animals, as well as plants.  I’m a big fan of them.  However, their ecological value is hard to separate from some of the baggage that comes along with the species in today’s landscape.  For example, in Nebraska, most of our large grasslands are part of private ranches.  While there is much discussion about the (potentially positive) impact of prairie dogs on forage quality, and the idea that their holes cause lots of cattle to break legs is mostly mythology, there’s no question that prairie dogs compete for forage with livestock.  As a result, prairie dogs are seen as pests by most ranchers because they reduce the amount of forage (and thus income) produced by the areas they inhabit. 

Black-tailed prairie dogs have a big impact on grasslands. Depending upon your perspective, those impacts can positive, negative, or both.

Fans of prairie dogs and their associated ecological benefits might feel angry about ranchers eliminating prairie dogs from their land.  I understand that, but a more productive approach might be to consider ways to financially compensate ranchers for the losses they incur from prairie dogs.  It’s no more fair to expect ranchers to lose money by coexisting with prairie dogs than it is to expect a restaurant owner to give away food.  There might be some ranchers and restaurant owners who can afford to do that, but others who are riding a tightrope between profit and loss aren’t bad people for trying to stay in business.

Aside from the financial aspect, the other big obstacle to increasing prairie dog numbers on private ranches is that there is a big social stigma attached to them.  Ranchers who co-exist with prairie dogs risk scorn from their neighbors.  Social norms are real and important pressures that influence how we all behave.  Just as it takes a lot of confidence and bravery to dress in a drastically different way than your peers at a business meeting, it can be difficult to be that rancher in a rural landscape where everyone knows and relies on each other. 

In addition to the social stigma, prairie dogs like to spread out, so neighbors have a legitimate worry that one rancher’s prairie dog population might spill over into another’s.  Because of both the financial and social implications of that, the situation mirrors that of a landowner’s worries about the noxious weeds on a neighbor’s land.  In fact, there is a statute in Nebraska that gives county officials the ability to control prairie dogs on private land to prevent their spread, though that statute is not frequently enforced, as far as I know.

Prairie dogs are doing better on some public lands, though it sounds like disease and other pressures are still significant.  There certainly aren’t many places where the size of a prairie dog town is large enough to host a viable population of the once-thought-to-be-extinct black-footed ferret.  For that to change, we’ll probably need to figure out a way to deal with the aforementioned issues on private lands.  It’ll take some creativity and patience, and probably some significant funding.


shoreacres  asks:

After some thought, I realized that I’ve never been in the state of Nebraska, apart from one quick trip across I-80. I think a visit’s in order. Which grasslands, preserves, forests, or refuges should be on my must-see list? And which guides or books could I begin reading now to prepare for a trip? I probably could manage two weeks.

And I have to ask: after looking at Google’s satellite map, what kind of land form is that ripple-y area bounded by highways 20, 27, and 83 — west of the Valentine refuge? I can’t remember seeing anything like it. The land looks extruded, like spaetzle!

Linda, you’ve got a wonderful way with words.  First, the spaetzle landscape is the Nebraska Sandhills, 12 million acres of sand dunes covered in prairie and wetlands. It really does have a unique look from above, doesn’t it?

The Nebraska Sandhills is an amazing prairie landscape.

Nebraska has plenty of great sites. There are some pretty nice oak woodland sites with tallgrass prairie ridges in the east.  A couple public examples are Indian Cave State Park and Fontenelle Forest (you could also skip across the Missouri River to see the Iowa Loess Hills).  Elsewhere, most of the best remaining tallgrass prairie in southeast Nebraska is on private land, but Wachiska Audubon has worked to protect some of those remnants, and some are publicly accessible.  During college, I spent a lot of time at Nine-Mile Prairie in Lincoln, and it is still a nice place to wander around.  Spring Creek Prairie, just west of Lincoln, is a great site too, with some excellent interpretative displays.

Further west, check out the prairies owned by Prairie Plains Resource Institute.  Don’t skip Gjerloff Prairie, a wonderful loess hills site with interesting topography and habitat, as well as a view of the Platte River.  The Nature Conservancy’s Platte River Prairies, of course, are also nice (if I do say so myself) and we’re working to improve our hiking trails and visitor facilities over the next few years.  Let me know if you’re coming and I’ll try to meet you out there!

In the Sandhills, both the U.S. Forest Service and U.S. Fish and Wildlife Service have big public areas to visit and they’re all worthwhile.  Crescent Lake and Valentine National Wildlife Refuges are especially nice if you want to see some beautiful groundwater wetlands/lakes.  The amazing Niobrara River also has a number of publicly-available sites, including the Niobrara Valley Preserve, Fort Niobrara, and Niobrara State Park, to name a few.

In the panhandle, Fort Robinson, Chadron State Park, Toadstool Park, and the Wildcat Hills are among my favorites.  I’m sure other Nebraskans can help with other recommendations, especially with areas I’m not as familiar with.  For example, I love the northeast and southwest portions of Nebraska but don’t spend enough time there to know the best locations to visit. 


Laura asks:

How do you feel about bats?

Bats are adorable, amazing, and sadly misunderstood.

How do you feel about smammals?

Smammals are adorable, amazing, and sadly misunderstood.

What’s your favorite dinosaur?

Wow, it’s been a long time since I spent much time thinking about dinosaurs, but if pressed, I’d probably choose Pachycephalosaurus.

Small mammals, aka smammals, play lots of important roles in prairies. They’re also stinkin’cute.


Ellen Rathbone asks:

Legit question: After moving to the midwest, I’ve had to learn a lot about the prairie (and savannah) ecosystem(s). One of the early things I had read was that while bison provided valuable ecological services to the system, cattle were much harsher on the landscape and should not be promoted (this had to do with hooves, movement patterns, and possibly diet as well). THEN I read a piece that said there was no real difference – grazers are grazers, hooves are hooves. It sounds like you may fall in the second category, but I’d like to hear/read your thoughts on this. Thanks!

Not surprisingly, I do have thoughts to share on this topic!  In fact, I’ve spelled out a lot of those thoughts in a post written back in 2014. You can read that, but I’ll summarize a few points here too. 

Bison at The Nature Conservancy’s Niobrara Valley Preserve are in 10,000 acre pastures, giving them plenty of room to move around the landscape.

Cattle and bison have pretty similar diets, if given the same choices and pasture sizes.  Bison might be a little more selective toward grasses, but both eat primarily grasses and fill in nutrient needs with wildflowers when they need them.  Some of the biggest differences are behavioral, especially related to the use of water and trees/shade.  Bison don’t hang around water or trees much.  They tend to get a drink, rub on a tree, etc., and then head back out into the open prairie.  Cattle often stand around in water during the summer, mostly (as I understand it) to escape biting flies that attack their legs.  They also seek out shade trees and will loaf around those trees enough that they’ll disturb vegetation significantly there.  As a result, there are some issues with pollution, erosion, and vegetation disturbance that can come from those cattle behaviors.  Most of that can be mitigated by management – fences, limiting/rotating access to water/trees, etc., so that there is no permanent damage done. 

Bison also come with hassles.  In most cases, prairie managers have to own the bison and keep them on the prairie year-round.  That means annual roundups, good fences and corral systems, and a lot of constant responsibility.  Ranchers often own their own cattle too, of course, but it’s usually their full time job to take care of them. Managers of public or private prairie preserves usually just bring cattle in on a temporary lease basis, so the animals are there for up to 6 months or so per year and then go somewhere else.  Typically, the owner of the cattle is in charge of any doctoring that needs to happen too, so the prairie manager’s job is easier than it is as a bison owner.  There’s a lot of variability in how all that works, but that’s generally the way it goes.

In short, both cattle and bison can do positive things for prairies if they’re managed thoughtfully.  Both can also be problematic – both logistically and ecologically – if they’re managed poorly.  If grazing is an important component of the management objectives for a particular site, the bison vs. cattle question often comes down to scale and logistics.  Unless you’ve got a few thousand acres of prairie, bison are probably not very feasible, both from cost (fencing/corrals, etc.) and ecological (bison like/need bigger areas to feel and act like bison) perspectives.  Cattle provide more flexibility in management options, and can be used in relatively small prairies, but also need a little more planning to prevent some of the potential issues surrounding water and trees.

Photos of the Week – September 25, 2020

Last week, while checking on our prairie, I noticed a couple big congregations of ‘woolly bear’ caterpillars. I found several clusters of hundreds, which was impressive. They didn’t seem to be tied to any particular plant species or habitat structure – just apparently random groups. The numbers were impressive.

Yesterday, I was back out at the prairie to catch the sunrise and I saw the caterpillar clusters again, but this time, there was a stark difference. Many of the caterpillars were way up high in the canopy – at the tops of grasses, forbs, and even fence posts. And many of those high elevation caterpillars were dead. Some were still intact, but others were withered or empty-looking shells of their former selves. The calm winds, dewy conditions, and warm-colored sunlight made for some great photography, but I spent much of the time distracted by the mystery – why were all these caterpillars climbing up high and dying?

It was easy to find caterpillars to silhouette against the rising sun. After about an hour, I ended up with over 50 different caterpillar photos I liked well enough to edit/process (including all my caterpillar shots, not just the sunrise silhouettes). I did not include all 50 here, but I was tempted… Nikon 105mm macro lens, ISO 400, 1/800 sec, f/11.
I count six caterpillars in this photo, including one at the very bottom (center) and two on the right side. There were patches of similar density the size of roughly a quarter to half an acre at a time. Nikon 18-300mm lens at 52mm. ISO 400, 1/125 sec, f/11.
Caterpillars on big bluestem. Nikon 105mm macro lens, ISO 500, 1/640 sec, f/6.3.

I believe the caterpillars I saw were larvae of the Virginian tiger moth (Spilosoma virginica). The species can be really variable in color, so while I found both pale creamy-colored caterpillars and almost bright orange caterpillars, they could still all be the same species. (It’s also very possible that there were multiple species – I’m not an expert on moth caterpillar identification!)

The climbing behavior reminded me of stories I’ve read and heard about insects that are attacked by parasitoids, fungi, or viruses that alter their behavior before eventually killing them. In the case of some fungi and viruses, insects are compelled to climb up high before dying, which helps the spores of the infecting agent spread widely after the larva dies. It’s certainly possible something like that is at work here, though the appearance/condition of the dead caterpillars I saw didn’t match the kinds of descriptions I found during an online search last night.

Parasitoids seem like a likely possibility – either flies or wasps. Stephen Spomer of the University of Nebraska-Lincoln says he has seen similar behavior in the past with tiger moth larvae and has reared parasitoids from them (entomologists are the coolest…). However, neither of us could explain why parasitoids would stimulate climbing behavior. Stephen suggested there could also be multiple factors at work (parasitoids and fungi, for example). If so, that’s pretty rough for those cute little caterpillars.

Here’s one of the more orange-colored caterpillars I found. Nikon 105mm macro lens, ISO 500, 1/250 sec, f/9.
More caterpillars at the tops of grass stems. Nikon 105mm macro lens, ISO 500, 1/125 sec, f/16.
Here’s one that is clearly dead – still clinging to the stem, but not with any active muscle power. Nikon 105mm macro lens, ISO 500, 1/250 sec, f/11.
This dead caterpillar seems to be hollowed out, which I take as likely evidence of a parasitoid insect larva that fed on it. Nikon 105mm macro lens, ISO 500, 1/250 sec, f/13.

I did see some caterpillars that were still acting normally – crawling around on plants and feeding. They were also down at a more reasonable elevation in the vegetation, rather than at the pinnacle of the highest plant they could find. I hope they escaped whatever afflicted their colleagues and weren’t just in an early stage of infection that hadn’t fully kicked in yet.

I’d appreciate hearing from anyone who knows more about what I was seeing and can provide more explanation. I love a good mystery, but I love fascinating natural history stories even more. There’s got to be at least one good story here and I’d really like to hear it. It’s easy to feel badly for the caterpillars, and that’s certainly a reasonable emotion. At the same time, parasitoids and other possible infection agents also have an important role to play in controlling the populations of insects like this. I think it’s possible to feel bad for individuals while appreciating the broader picture that led to their affliction (even if we don’t yet understand that picture fully).

This one was still alive, but maybe not for long? Nikon 105mm macro lens, ISO 500, 1/100 sec, f/18.
And another… Nikon 105mm macro lens, ISO 500, 1/200 sec, f/14.
This was one of the caterpillars that seemed to be acting normally – feeding on heath aster (Aster ericoides) and not climbing high in the prairie canopy. Nikon 105mm macro lens, ISO 320, 1/80 sec, f/16.

Tiger moths have been around for a long time and are likely to continue existing long into the future. I’m sure they’ve been dealing with whatever parasitoid or other organism is attacking them for a very long time. I’m fascinated by what I saw yesterday and would like to learn more about it. I also wish both organisms luck. The caterpillars that survive have a long winter ahead of them and the mystery organism will also have to get through the winter so it can continue its own life cycle next year. Complex interactions keep prairies healthy and resilient. Carry on, little friends!