Regal Fritillary Butterflies in the Platte River Prairies – 2011

We completed our second season of regal fritillary butterfly data collection this summer.  Funded by State Wildlife Grant funds from the Nebraska Game and Parks Commission, our surveys are designed to help us better understand how this butterfly species is responding to our prairie restoration and management work.  The species is doing very well in Nebraska, and the central Platte River valley has some of the highest concentrations of regals in the country, but the species is of conservation concern because of it’s extreme rarity elsewhere in its historic range.  In addition to informing our work, we hope that studying the species where it’s common can help inform conservation efforts in those places where it’s rare.

Some people may be surprised to hear that regal fritillary butterfly populations are thriving in the central Platte River valley – a landscape dominated mainly by rowcrop agriculture and degraded prairie plant communities.  The neighborhood around our Platte River Prairies is about 30% grassland – a higher percentage of prairie than many eastern tallgrass landscapes, but certainly not a large unbroken prairie landscape.  Moreover, Platte River grasslands tend to have long histories of chronic overgrazing and broadcast herbicide use which has left them with limited plant diversity.  Even most of our annually-hayed prairies are missing many wildflower species that would be expected to be dominant in those prairie types.  The fact that regal fritillaries are thriving in this landscape seems counter to some of what is published about the species’ reliance on “high quality prairie”, but they’re here nonetheless! 

Regal fritillaries rely on violets as the sole food source for their larvae.  In our Platte River Prairies, the only perennial violet species we have is the common blue violet (Viola sororia).  In much of the eastern tallgrass prairie, prairie violets (V. pedatifida) or bird’s foot violets (V. pedata) are thought to be the preferred species, but we don’t get those species in our area.  Fortunately, the common blue violet thrives in pastures with long histories of annual intensive grazing, so the supply of larval food sources is not limited in our landscape.  It may be that the abundance of violets and the amount of grassland left in the valley are the two primary reasons for the regal fritillary’s continued success here.

Common blue violets (Viola sororia) are abundant in our degraded prairies - along with lots of Kentucky bluegrass. The species appears to support strong regal fritillary populations.

A brief report of our findings from 2011 can be found in this PDF, but I’ll lay out a few of the highlights here.  First, the seasonal patterns of butterfly abundance we’re seeing seems to match what we know of the life history of the species.  Males emerge first (late June), with highest numbers occurring in areas with relatively high amounts of thatch and lots of violets.  Those males tend to spend the next couple weeks flying around the same place they emerged from until the females also emerge and mating takes place.  That mating period is when we see the most fritillaries along our transects.  Following that, the number sightings drop as males begin to die off and females enter a period of “reproductive diapause”, during which they spend much of their time sitting around in the shade.  Finally, in late August, we see a little bump in our numbers again as females begin flying around and laying eggs.  (Those eggs then hatch, and the larvae – if they find enough violets to eat – will overwinter in the thatch.)

The effects of prescribed fire on regal fritillaries and other butterflies is a frequent topic of discussion among ecologists.  At our sites, we definitely see the highest numbers of regals emerging in June and July from prairies with high numbers of violets and with a build up of thatch.  Prairies that were burned in the spring have very few fritillaries during that peak period of emergence and mating – the larvae almost surely perish in spring fires.  However, during the summer of 2011, two of our top three sites for nectaring activity had been burned in the spring of that year.  It may be that in landscapes of relatively abundant habitat, a mixture of burned and unburned areas can complement each other by providing high quality larval habitat (unburned) and nectaring habitat (burned). 

In addition to prescribed fire, our other major management tool is cattle grazing – and the two are often combined within our various patch-burn grazing systems.  The burned areas mentioned above where nectaring activity was high were also being grazed.  Under our light stocking rates, cattle focus primarily on grasses, leaving most wildflowers to bloom – making them available to pollinators, including regal fritillaries.  Under higher stocking rates, fewer wildflowers escape grazing and regal fritillary are lower.  However, even areas that are burned and intensively grazed recover quickly, and within a year or two (as cattle focus on more recently burned areas) become hot spots for regal fritillaries again.  As stated earlier, it appears that a mixture of management treatments across a landscape with fairly abundant habitat is compatible with successful regal fritillary populations.

After our 2010 butterfly surveys, I posted a report on the nectar use by regal fritillaries and other butterfly species.  Those 2010 surveys included a slightly different mixture of prairies from our 2011 surveys, and included some transects where we counted all butterfly species.  Within that context, the clear favorite nectar plant was hoary vervain (Verbena stricta).  In 2011, vervain was still among the top nectar species for regal fritillaries – particularly in degraded remnants where it can be very abundant – but it was not quite as dominant as in last year’s surveys.  I think this was mainly because we included more restored prairies in our surveys this year, and the diversity of flowers was higher in those sites.  Even so, hoary vervain tied for first place in nectar species use with the combination of common and showy milkweeds (Asclepias syriaca and A. speciosa), followed closely by bee balm (Monarda fistulosa) and various thistle species (Carduus nutans and Cirsium spp).  It’s important to point out, however, that we only had 27 sightings of nectaring regal fritillary butterflies in 2011 (out of 352 total sightings), so our sample size was fairly limited.

Regal fritillaries in the central Platte River valley really like hoary vervain (Verbena stricta) as a nectar plant. Vervain survives intensive grazing very well, so it can be abundant in some of our more degraded pastures, as well as in our restored prairies.

Among those 27 sightings of regal fritillaries nectaring, all but four of them were in restored prairies (former crop fields).  At least based on the data we’ve collected so far, it appears that our regal fritillaries are tied to degraded remnants (lots of violets) for larval production but move into our restored prairies (lots of nectar plants) later in the season.  A quick and dirty correlation analysis showed that after the mating season was over, butterfly sightings were most likely to occur in portions of prairie with high abundances of their favorite nectar plants – but there was no such correlation prior to or during the mating season.  Again, a mixture of habitat types (this time, restored and remnant) appears to provide complementary resources for the butterflies in the Platte River Prairies. 

Clearly, regal fritillaries managed to survive just fine along the Platte River before our restored prairies were available, so it’s not that we’ve saved the species through our restoration work.  Intensively grazed pastures tend to have high numbers of hoary vervain flowers for nectaring, and some hayed prairies in the valley contain good numbers of milkweeds and other nectar species as well.  However, watching the behavior of fritillaries when areas of high nectar plant abundance (e.g., our restored prairies) become available may tell us about what their preferred habitat conditions are. 

Thistles, including this musk thistle, are among the favorite nectar plants for regal fritillaries - along with hoary vervain, bee balm, and common milkweed. At least for now, musk thistle is surviving just fine in the Platte Valley. (hooray?)

I feel pretty confident that regal fritillaries are managing to survive within the context of our current prairie restoration and management work.  However, we’re still not able to figure out where they’re laying their eggs.  According to the literature, regal fritillary females don’t lay their eggs on violets (why??) and no one is even sure if they select locations near violets.  I sure hope our regal fritillary females return to remnant prairies (where violets are abundant) to lay eggs, rather than laying them in our restored prairies.  If our restored prairies – with their abundant nectar plants – are luring those females away from prime egg-laying habitat, that’s not a good thing.  To date, we just can’t get enough sightings during that late summer egg-laying period to figure out what’s going on.  We even tried following females around to see if they were laying eggs but that turned out to be pretty difficult.  I guess since the population seems to be strong I’m not going to worry about it too much, but I’d still like to know what they’re doing. 

Because of the limited time we can devote to this project, it’s necessarily more of a pilot project than a full-blown research effort.  If there are scientists out there who would be interested in following up on our initial work, I’d be more than happy to work with you. 

In the meantime, you can see read the report from our 2011 surveys here, including lots of fun graphs and tables.

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About Chris Helzer

Chris Helzer is an ecologist and Eastern Nebraska Program Director for The Nature Conservancy. He supervises the management and restoration of approximately 4,000 acres of land in central and eastern Nebraska - primarily along the central Platte River. Chris is also the author of "The Ecology and Management of Prairies in the Central United States", published by the University of Iowa Press.
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20 Responses to Regal Fritillary Butterflies in the Platte River Prairies – 2011

  1. The development of favored violet species populations in restorations would seem appropriate, but I know from experience this is easier said than done.

    • Chris Helzer says:

      James T – We’re actually working to increase the number of violets in our restored prairies. Getting through the initial seedings is tough because of seed harvest limitations. We’ve tried raising them in our nursery and harvesting seeds, but are now just direct transplanting them from our remnant populations into our restored prairies. Eventually, we’ll limit any potential negative issues we may or may not have with regals – I was hoping our surveys would help us see how much of a priority we should make that violets effort…

      • James McGee says:

        It would be a worth while project to have someone follow the Regal’s for a season and see what they do. I’m sure nectar sources are not as limiting as reproduction issues. It would be interesting to see where ovapositing occurs and track the larva. I am curious if these butterflys return to the same sites to breed or have a more random egg dispersion strategy.

  2. Dan Glomski says:

    Chris, thank you for this report. Regals are such striking symbols of the prairie; during a butterfly hike last September, I told the kids about regals and they got all excited when we found one (a tattered female).
    Last year I tagged along during the monitoring of a transect, and it didn’t look terribly difficult. Could this possibly form the basis of a citizen science project?

  3. Doug McEvers says:

    Great work, Chris

    I have become very interested in the Regal Fritillary after seeing and taking photos of them on our NW MN prairie in 2010. Looking at the time stamp on one of the photo’s of a male and female Regal was July 25, 2010 and they were on a cluster of Prairie blazing star (Liatris pycnostachya). This area was unburned that season and the blazing star was 1/2 bloom and farther along than the blazing star (not blooming) in the burned area adjacent.

    This year I saw a Regal on July 16 on a burned area sitting on Swamp milkweed (Asclepias incarnata). The wings were not open so I can’t say as to the sex. My goal next year is to watch more closely for them and hopefully refine my management plan so they increase. The blazing star this year were in the same stage as last year on July 31, about 1 week later, probably due to a somewhat later spring warmup.

  4. David says:

    Chris,

    I am curious if you have received any pressure for establishing a permanent non-fire refugia for the Regals and other butterflies?

    David

    • Ted says:

      I’m with David on this. Seems like a really good question. Perhaps many restorations would benefit from having a few areas, which are rich with larval and adult food sources, that are kept permanently unburned or else are on long cycles for burning.

    • Chris Helzer says:

      David and Ted,

      Several answers to this. First, no, I’ve never had any pressure to establish a permanent non-fire refugia. Largely, I think, because that philosophy (?) is more of an eastern thing at this point. We’ve got enough habitat, and enough prairie goes unburned in Nebraska by default, that it’s just not seen as a big conservation issue.

      Second, with regal fritillaries at our sites in particular, I’m not very worried about their future based on our management. They’re extremely common throughout the eastern half of the state (one of our more abundant butterflies on 4th of July butterfly counts) and no one seems to worried about their fate.

      Third, I’m not sure I like the idea of any kind of permanent refugia (fire, grazing, or otherwise). My view of prairie function is that grasslands are very dynamic systems and have evolved under constantly shifting conditions from year to year. Species that like thatchy prairie would have had to be able to hunker down or move large distances throughout the last 10,000 or so years in order to survive. In the eastern tallgrass where there are very few small remnants left in some places, I think it’s worth thinking about individual species’ needs, and under extreme conditions, I guess refugia are worth some thought. But you’re creating some potentially big stewardship headaches (possibly including facilitating invasives – trees and otherwise – that could spread beyond the refugia) and likely putting other species at risk from perennial idle management. Managing for single species should be considered very very carefully, I think – ESPECIALLY when habitat is already limited for the other species that might be managed against. In areas of more habitat, the risk to other species is probably lower because there’s more overall habitat around for everyone to find what they need, but I still don’t think it’s a good idea. I know many people disagree with this. It’ll probably be a good blog post sometime, and will create fun discussion.

      I guess it boils down to the idea that in almost every case, I’m going to trust prairie species’ ability to move around (or hunker down) in order to find what they need as management shifts. Now, I do advocate against burning an entire isolated prairie. No question that’s a bad idea for inverts and other species. But in most cases, I don’t have a problem with burning a portion and leaving a portion unburned, and then shifting those management units around over time. IF there was a situation where you had a small clump of plants of a species, and that was the only clump in the landscape, and if you had an insect species that would be very damaged by burning that clump, I could maybe see not burning that very small area where the clump of plants is. Maybe. But it would take some convincing before I’d change the management of the entire site (or a large portion of it) just to try to save a species like that. Mainly because I doubt the species is going to be viable long-term anyway, and I would be leery of putting the rest of the prairie community at risk in a low-percentage attempt to save one species. Especially in a landscape where there aren’t many prairies anyway.

      Very long and rambling answer – sorry. Will try to coalesce it into a more clear blog post at some point. Thanks for the question.

      • David says:

        Chris,

        Tis the answer I expected, but for me, as an eastern tallgrass guy, one that I struggle with. It is hard not to take note of work done (i.e. research with management recommendations) by very dedicated people trying to help an at-risk species that they love. At the same time, it is hard not to take note of equally dedicated people recommending counter management practices to protect the at-risk species that they care about. This is where we find ourselves, managing small, degraded ancient relics which harbor many rare species that have conflicting management needs. I remember back to when I was young to fire and how exciting it was to learn how to work with it and thinking all the time we were helping to bring back a lost ecosystem. I still, in general, think this is true. Now, however, when I pick up a drip torch (and antacids), the sureness of my youth has become clouded by the doubt of my aging years. I think for saneness, one is wise to hold on to a philosophy that the ancient prairie ecosystem is smarter than us all and its inhabitants can find their way. But still I wonder and doubt wanders in. I remember a set of book on tapes that I listened to long ago on a very long drive. I do not remember much about the story line only that it was about an old trapper who was still trying to hold on to the only thing he knew how to do (trapping) during a now modern era with suburbia rapidly consuming anything resembling wilderness. When the law finally caught up to the old trapper, wanted for poaching of endangered animals, this quote by one of the leading characters in reference to the old trapper has stuck with me. “The land around him grew fragile.”

        David

        • Chris Helzer says:

          David – I understand your struggle. Far be it from me to be the final arbiter of how you or others manage their prairies. I just give my perspective, and try to be sure to justify it based on my own context (landscape and philosophical). There are no easy answers when trying to conserve biological diversity – or individual species – in small isolated prairies. There just aren’t.

  5. James McGee says:

    I like the burn only half per year philosophy. Even though most prairie species appear to survive burning. It may cause their population to crash, but at least a small number typically survive for repopulation.

    In a dry gravel hill prairie near my home they burn the entire site every year. Their thought is burning frequently prevents an accumulation of fuel. They believe annual burning is best for the insects because it keeps the fire intensity from ever getting extremely hot.

    I really do not think there is one answer to these questions. In the aforementioned dry gravel hill prairie I have noticed (invasive) black locust has become establish even though annual burning is occurring.

    In some really high quality prairies it seems other things are occurring which help prevent invasion of woody species. These prairies may resist colonization by native woody species, but have little resistance to the invasion of highly competitive introduced species.

    In the absence of fire some fens and dry prairies have survived as islands that are now completely surrounded by woodlands. These ecosystems have been able to persist for at least decades without fire. Their existence gives clues to the change in the ecosystem that has occurred from the period which allowed these species to expand into these habitats. It is not that I think fire is unimportant, I just think other things we do not fully understand may be just as important to the survival of certain prairie ecosystems. At least this appears to be true on the Eastern deciduous forest transition zone where I am located.

    James

    • David says:

      James,

      Interesting points and watch out for that black locust. It loves to invade our sand prairies. We will not burn through a site with black locust until it is controlled by other methods.

      We too have observed your point about fens. In the calcareous fens we have around us, the plant community is specialized and they do resist invasion. We have found that reed canary grass can barely hold on in calcareous fens and it is easy to suppress in these situations.

      David

    • Doug McEvers says:

      James,

      I was burning only half per year until I discovered we had Regal Fritillary butterflies. Now I am working on a 3 year burn rotation so there is always a portion with last year’s duff that will be undisturbed the next season. I am finding as my restoration ages, the plant community has become more dynamic because of the life in the soil, in my opinion. The grassland remains robust even as the years between burns increases.

      A neighboring property that is native prairie and was undisturbed for many years is now being overgrazed. So what was most likely the Regal’s refugia is currently unavailable and I must provide this on my own acres with a 3 year burn interval. Three years between burns also works well in controlling White sweet clover, a 2 year plant.

  6. Pingback: Status of Platte River Prairies Regal Fritillaries « Lep Log

  7. Pingback: Regal Fritillary Butterflies in Burned and Grazed Prairie | The Prairie Ecologist

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