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Article

Birdfoot Violet (Viola pedata) in a Minnesota USA Dry Bluff Prairie: Population Assessment of a Preferred Host Plant of the Threatened Western Regal Fritillary Butterfly (Argynnis idalia occidentalis)

by
Chloe Peterson
,
James Duffrin
and
Neal D. Mundahl
*
Program in Ecology and Environmental Science, Department of Biology, Winona State University, Winona, MN 55987, USA
*
Author to whom correspondence should be addressed.
Conservation 2025, 5(4), 58; https://doi.org/10.3390/conservation5040058
Submission received: 23 August 2025 / Revised: 19 September 2025 / Accepted: 25 September 2025 / Published: 9 October 2025
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Abstract

A self-sustaining population of birdfoot violet (Viola pedata), a host plant for the threatened western subspecies of regal fritillary butterfly (Argynnis idalia occidentalis) caterpillar, was examined during a single year from April to June 2021 on a small, 3.1 ha dry bluff prairie hillslope within the Whitewater Wildlife Management Area in southeastern Minnesota USA. Assessments were conducted to determine if violet populations on small prairie remnants could support seed collecting to establish new populations nearby. Ten transects and five random plots were used to assess violet density and monitor violet growth, reproductive phenology, and seed production. Violet densities were high (>5 plants/m2), with greatest densities at middle elevations on the hillside in the middle of the prairie rather than near the edges. The total population of birdfoot violets on the hillside was extrapolated from density estimates based on 200, 1-m2 plots to be >62,000 plants. Seed set was low (less than one pod per plant) but nearly 400,000 total seeds were produced during the 2021 growing season. More than 3000 seeds (<1% of estimated seed production on the study hillslope) were collected for out-planting to establish a new violet population in nearby Whitewater State Park. Some small bluff prairies in southeastern Minnesota and elsewhere under certain conditions may sustain violet populations large enough to permit seed collecting to establish additional populations during restoration of native prairie communities. These ultimately should provide much needed habitat for regal fritillary butterflies to partially compensate for ongoing habitat losses.

1. Introduction

The birdfoot violet (Viola pedata L.; Violaceae) is a perennial wildflower native to most of the eastern USA, ranging from the Atlantic coast westward to Nebraska, Kansas, Oklahoma, and Texas and from the Great Lakes states south to the Gulf of Mexico (Figure 1) [1,2]. It can grow in a wide variety of soils ranging from those on dry, rocky, and poor uplands to well-drained and organic-rich soils in tallgrass prairies [3]. The species often is restricted to undisturbed, high-quality prairie and savanna habitats [2,3,4,5,6]. Its flowers attract a variety of pollinators (bees, skippers, small butterflies) during mid- to late-spring [2,7], the leaves are eaten by several species of fritillary butterflies (Lepidoptera: Nymphalidae) during spring and summer, and its seeds are collected and eventually dispersed by ants that use the oil-rich fleshy blob (elaiosome) on the seed surface as food [2,8].
The regal fritillary (Argynnis idalia) is likely the rarest butterfly whose larvae rely almost exclusively on violet leaves as food [5,6,9,10,11,12,13]. The eastern subspecies (A. i. idalia) is federally (i.e., USA) endangered and the western subspecies (A. i. occidentalis) is federally threatened [12]. In addition to the birdfoot violet, other Viola species (prairie violet Viola pedatifida; lance-leaved violet Viola lanceolata; arrow-leaved violet Viola sagittata; sand violet Viola fimbriatula) may support regal fritillary populations [13]. However, the success of many regal fritillary populations in the USA is largely dependent on abundant and healthy populations of the two most common species, birdfoot violet and prairie violet [9,13,14,15]. The dependence of regal fritillary appears to shift somewhat from birdfoot violets in eastern North America more to prairie violets in the midwestern states [9,13,14,15].
Attempts have been made to enhance the availability of birdfoot violet for regal fritillary populations. For example, new populations of birdfoot violet have been established in Iowa and Illinois by translocating plants collected from existing large populations in large prairies to new sites or by seeding violets directly into new habitats [16,17,18]. However, the species typically has been difficult to reintroduce due to disturbances such as prescribed burns used to manage restored prairies interfering with seed or seedling survival [3,18]. Working in partnership, state governmental agencies, citizen volunteers, and a regional plant nursery in southeastern Minnesota USA chose to explore a third approach: collecting seed from a wild population, germinating the seeds and propagating violets under controlled conditions, then planting those violets during a prairie restoration project [18].
Before implementing this strategy, project partners needed to locate and assess small local prairies with V. pedata to choose a population that (1) would not be impacted negatively by limited seed collection, and (2) that would have the regional genetic ecotype most likely to be best adapted for success in the local environment of the restoration project site. Our study describes the process undertaken to assess a single population of birdfoot violet as a possible restoration seed source candidate. We conducted a simple preliminary population assessment on a single isolated dry bluff prairie within a state-owned wildlife management area and documented plant growth, examined reproductive phenology, and estimated seed production during a single springtime growing season. We aimed to determine whether a small prairie with a dense violet population could provide sufficient seed for restoration without compromising population viability.

2. Study Site

Minnesota lies in the northwestern portion of the range of birdfoot violet in the USA [19]. In Minnesota, the species is restricted to the east-central and southeastern regions [19]. Our study site (Figure 1) was located within the state-owned Whitewater Wildlife Management Area (WWMA), which encompasses 11,088 ha of mixed hardwood forests, prairies and savannas, river floodplains, and wetlands along the Whitewater River in southeastern Minnesota [20]. The core mission of the WWMA is to preserve, protect, and manage wildlife habitats while maintaining public access for recreational activities.
Prairies and savannas comprise 2185 ha (or nearly 20%) of the WWMA. These areas, which provide habitats for a diverse array of grassland-specific small mammals, songbirds, amphibians and reptiles, and insect pollinators, are actively managed via prescribed burning, invasive plant species removal, and interseeding [21]. For example, savanna and prairie habitats within the WWMA have been managed previously to protect the federally threatened Karner blue butterfly and its favored plant community [22]. Included among the WWMA’s upland grassland habitats are dry bedrock bluff prairies [23], unique sites located on steep, south-facing hillslopes, often rising >100 m in elevation from valley floors. These dry bluff prairies typically are small (<5 ha), isolated from similar prairies by upland forests, and characterized by thin, sandy soils, sandstone and limestone outcrops, and high evaporation rates [23]. Dry bluff prairies are remnants of a rare, fragmented ecosystem in the Driftless Area of Minnesota, Wisconsin, Iowa, and Illinois, threatened by fire suppression and invasive species and inhabited by many rare plant and animal species [24,25,26,27]. These prairies typically support plant species adapted to drier, rockier soils than those living in the richer and moister soils of tallgrass prairies to the south and west [23,28,29]. The WWMA manages dozens of these dry bluff prairies, specifically using fire, grazing, and mechanical methods to suppress encroachment of these habitats by woody invasive plants.
There are 15 dry bluff prairies within a 730-ha section in the north-central portion of the WWMA on the eastern side of the Whitewater River. These bluff prairies, ranging in size from 0.1 to 4.4 ha, all have southerly to southwesterly aspects, located downslope of four parallel ridges that are situated perpendicular to the main river valley. Valleys between these ridges lead into the main river valley and variously contain lowland forests, agricultural fields planted for wildlife forage, wetlands, and lowland prairie/savanna habitat.

3. Methods

3.1. Field Studies

Preliminary field studies began in early April 2021 to assess the birdfoot violet populations at dry bluff prairie sites within the WWMA. Although violets were present at several sites within the WWMA, difficult accessibility and/or very small violet populations (based on cursory examination; populations were not systematically assessed) at most sites eliminated those sites from further study. Consequently, WWMA and citizen volunteers with Friends of Whitewater State Park decided that our study should focus on violets present only on a single prairie hillslope (3.1 ha in total area; Figure 2A) that supported the largest violet population within the WWMA. We acknowledge that assessing only a single site reduces our ability to make broader inferences from our study, since other dry bluff prairies may have slightly different characteristics that could affect violet population densities and their success.
In late April, we began our surveys under permission of the WWMA. We surveyed the prairie hillslope (Figure 2B) to determine the total area of the portion of the hillslope occupied by violets and to measure violet densities. We found that violets grew on an area that was roughly trapezoidal in shape; 87.4 m wide across the top of the slope, 138.4 m wide across the bottom of the slope, and 100 m from top of slope to bottom. To assess violet densities, we used a series of transects and quadrats [3] to systematically survey the violet habitat. We established 10 transect lines, each 100 m in length, oriented upslope to downslope on the prairie hillside. Transects were roughly parallel and non-overlapping, spaced to cover the entirety of the hillside area containing violets. The lower end of each transect was located near the prairie/brush ecotone at the bottom of the hillside. Transects were positioned to avoid scattered trees/shrubs, bedrock outcrops, or other “interruptions” in the prairie habitat. Every 5 m along each transect, violet counts were made using a 1-m2 quadrat plot frame. The plot frame was placed directly on the transect line centered on each 5 m mark. The position of each plot along each transect (5 m, 10 m, 15 m, 20 m, and so on) and the number of V. pedata in each plot were recorded. We felt that the 5 m spacing between plots was a good balance that served to provide both fine detail on variations in violet density while also allowing for efficient censusing of the violet population.
From April 21 through June 6, violet growth and reproduction data were collected on nine dates from each of five, 0.25 m2 plots randomly selected (by tossing the plot frame) within areas of the prairie hillside with the highest apparent densities of violets (based on previous transect counts; Figure 2C). We acknowledge that monitoring only five plots is less than ideal to adequately assess potential variability among individuals within this population. However, other work obligations and the unavailability of citizen volunteers to assist with monitoring necessitated this decision. Plots were marked with flags throughout the study period to permit repeated assessments of the same plants through time. Plots were labeled A through E, with violet positions mapped within each plot (Figure 3). On nine dates throughout the 45-day observation period, data on the number of leaves, number of flowers, and number of seed pods were recorded for each plant in these plots. We also recorded basic weather conditions (e.g., freezing nighttime temperatures, abnormally warm daily temperatures, periods without precipitation) that might be useful for interpreting violet growth and the timing of reproductive stages.
For three days later in June, after determining that the violet population was large enough to support small-scale seed collection, seed pods of birdfoot violets were collected as they ripened and before natural seed dispersal occurred. Mature seed pods were gathered by hand and allowed to air-dry together in the laboratory, arranged in a single layer within plastic trays placed in a constant-flow ventilation hood. Once seed pods were fully dried, seeds were removed carefully from the pods by hand. Seeds from 26 randomly selected seed pods were counted as they were removed to estimate seed production. Seeds from all seed pods were combined and the total dry mass of all seeds collected was measured (nearest 0.0001 g) using an analytical balance (Denver Instrument model APX-100, Bohemia, NY, USA).

3.2. Data Analyses

To determine violet population size (±95% confidence interval) on the dry bluff prairie hillside, the average violet density based on the 200 plots was multiplied by the total area of the prairie occupied by violets. The population estimate was then used to first estimate the total number of seed pods formed within the population, followed then by estimating the total number of seeds produced on the hillside during the 2021 growing season. Our phenology observations also permitted us to estimate what proportion of the violet population flowered during the 2021 growing season, and what proportion of flowers were pollinated and set seed.
Although we did not count (1) the number of violets from which we harvested mature seed pods, (2) how many mature seed pods were gathered from the WWMA bluff prairie, or (3) the number of seeds gathered, we were able to indirectly estimate these values by following a logical step-by-step process. First, we used an estimate of 917 dried birdfoot violet seeds per g [30] to convert our total dry weight of seeds collected into number of seeds collected. We then used our data on seeds per seed pod to estimate the total number of seed pods harvested. Finally, we used our data on number of seed pods per plant to estimate the number of plants needed to produce the harvested seed pods.

4. Results

On the WWMA dry bluff prairie, we tallied a total of 1101 violet plants across the 200, 1-m2 plots that we examined during April, resulting in an overall violet density (mean ± 95% confidence interval) of 5.51 ± 0.71 violets/m2. Extrapolating this density to the area (11,290 m2) of the hillslope occupied by violets produced a total population estimate (±95% confidence interval) of 62,206 ± 7966 violets.
Violets were not evenly distributed throughout the prairie, but generally displayed three areas of greatest concentration, with several plots exceeding 20 plants/m2 (Figure 4A). These highest densities were found across the middle-upper portion of the hillslope and the lowest violet densities were found across the top and bottom of the hillslope (Figure 4B), with violet densities differing significantly (Kruskal–Wallis H = 31.41, p < 0.0001) among the four levels. Seventeen percent of the plots surveyed had 10 or more violets present, whereas nearly one-third of the plots contained either one or zero violets (Figure 5).
During our 45-day violet observation period in spring 2021, the WWMA prairie area experienced a variety of weather conditions, some typical and others atypical for the region. These conditions are listed here as having the potential to effect violet growth or survival, but in no way are they meant to imply a direct cause-effect. As is typical for this region during spring, there were eight nights (4/20, 4/21/4/22, 4/24, 4/25, 5/1, 5/11, 5/12) when air temperatures fell below freezing (<0 °C), a potentially hazardous situation for growing plants. In contrast, five days (5/1, 6/3, 6/4, 6/5, 6/6) had atypical high air temperatures > 29 °C, with four of those > 32 °C. There also was one 6-day period (6/3 through 6/6) and one 7-day period (5/7 through 5/13) when no precipitation fell, both atypically long dry periods for this region during this season.
Twenty-seven violet plants were located within the five, 0.25 m2 plots that we monitored for 45 days to provide preliminary (due to small sample size) phenology data for violets at this location. Over the course of nine different dates, these plants collectively contained a maximum of 388 leaves, 48 flowers, and 12 seed pods on any one date (Figure 6). Across all nine observation dates, leaf, flower, and seed pod counts for individual plants were highly variable (Table 1). Typical plants were small, averaging only 10 leaves each. Flower and seed pod counts were especially low, averaging less than one flower per plant, with fewer than 10% of plants producing a seed pod. Leaf numbers were highest in late-April, although a secondary peak in abundance occurred in mid-May (Figure 6). Flower abundance peaked in early to mid-May, with all flowers gone by late-May, when seed pods were first observed (Figure 6). Reduced numbers of leaves and flowers were observed on 17 May following two successive nights with freezing air temperatures on 11 and 12 May (Figure 6). Only 74% (20 of 27) of the plants monitored produced flowers (74 total flowers observed; mean = 2.7 flowers/plant) and only 26% (7 of 27) of the plants eventually produced at least one seed pod (14 total seed pods observed; mean = 0.52 seed pods/plant). Overall, only 19% of the flowers observed eventually formed a seed pod. Again, we urge caution in interpreting these numbers, as they may have been impacted by the small number of plots/plants monitored.
When 26 randomly selected seed pods were carefully opened and their seeds counted, seed counts ranged from three to 29 in a single pod (mean ± 95% confidence interval, 12.3 ± 2.9 seeds/pod; median = 13 seeds/pod; range = 3 to 29 seeds/pod). The 26 seed pods examined contained a total of 319 seeds.
The three days of ripe seed pod harvest ultimately resulted in the collection of 3.6225 g of dry violet seeds. Based on the estimate of 917 dry violet seeds/g [30], we collected an estimated 3322 seeds from the WWMA dry bluff prairie population during our preliminary sampling effort. That number of seeds represents, on average, the contents of 270 seed pods, or the reproductive output of 519 violet plants on the WWMA hillslope during the 2021 growing season. Using the violet population size estimate confidence interval of between 54,242 and 70,174 plants, our seed collection efforts likely removed only 0.7% to 1.0% of the total population seed production during 2021. Expressed in an alternate way, the WWMA violet population we examined produced an estimated 347,000 to 449,000 seeds (or approximately 35 seeds/m2) during the 2021 growing season, sufficient to allow for the collection of 3300 seeds (or more) to start a new population of V. pedata in nearby Whitewater State Park.
Although we were not searching for them, we observed a single regal fritillary caterpillar feeding on a birdfoot violet during the seed collecting portion of our study in early June (Figure 7). No adult regal fritillary butterflies were observed at our study site during our April through mid-June study period.

5. Discussion

Birdfoot violet and several other species of Viola serve as larval food sources for the regal fritillary in different portions of its range [13,14,15], whereas a wide variety of common mid- to late-summer blooming flowers (e.g., thistles Cirsium spp., beebalm Monarda fistulosa, blazing stars Liatris spp.) provide nectar for adult regal fritillaries [4,13,31]. Due to the typically low densities [9,32], small size [17], and restricted habitats [16,17,33] of the Viola species, violet availability for foraging fritillary caterpillars is more likely a limiting factor than are the nectar sources for the adults [17]. Consequently, some studies [17,32] have suggested that only large prairies or prairie remnants (>67 ha) can sustain viable populations of regal fritillaries because only these large habitats will contain sufficient host plant numbers and leaf biomass to meet the larval food needs of a sustaining fritillary population [17]. However, ultimately site quality appears to be more important than site size in determining whether both violets and regal fritillaries will be present [3]. We recommend that regular population surveys of western regal fritillaries should be conducted on our study site and other similar dry bluff prairies in the WWMA to assess the status of this threatened subspecies.
Although our study did not focus on whether a regal fritillary population existed at our study site, our birdfoot violet density and population data and our sighting of a regal fritillary caterpillar (Figure 7) may contradict previous expectations for what size habitat may be needed for fritillaries. Although our dry bluff prairie was only 3.1 ha in size, we estimated that it supported >60,000 birdfoot violet plants. This large population size in such a small area was due to average violet density of 5.5 plants/m2. Violet densities at our study site were two to 62 times higher than those reported for multiple prairies in Iowa (with regal fritillary populations) that supported median violet populations (35,000 to 62,000 plants) similar to or slightly less than that at our study site but spread over areas up to 21 times larger than our prairie [9,30]. Prairies in Kansas, South Dakota, and North Dakota also displayed lower violet population densities (1.25 to 1.68 plants/m2) than those on our study prairie, but much larger prairie sizes resulted in total violet population estimates an order of magnitude (or more) higher than our dry bluff prairie estimate [32]. Density is certainly important in sustaining violet populations, but genetic diversity and successful pollination likely also play significant roles in the long-term persistence of violet populations capable of supporting regal fritillary populations.
The birdfoot violet is self-incompatible, requiring cross pollination among different individual plants for successful reproduction [34]. Consequently, the species relies on a diverse assemblage of bees, skippers, and small butterflies to transfer pollen among plants, offering both nectar and pollen rewards [7]. Although previous studies in Missouri have shown large percentages (60 to 90%) of birdfoot violet pistils receiving pollen [7], our data indicated that fewer than 20% of violet flowers at our study site were pollinated successfully and developed a mature seed pod, despite relatively high densities of violets that should improve chances of cross pollination. This low level of seed pod production would suggest either a scarcity of appropriate pollinators at our study site [3], or that pollinators on our study bluff prairie were more likely visiting multiple flowers on the same plant (inducing self-incompatibility and pollination failures) than they were visiting flowers on many different violet plants (leading to successful out-crossing) [34]. Factors such as climate change, habitat loss, and changing agricultural practices have significantly influenced the decline in pollinators in the Upper Midwest and elsewhere in the USA [35,36,37,38]. Freezing air temperatures during the flowering period at our study site also may have had some effect in reducing pollinator abundance and/or killing some flowers outright.
Despite the low rate of pollination in the violets at our study site, the average number of seeds produced per pod (12) was similar to average seed numbers (3.7 to 21.1 seeds/pod) reported for V. pedata previously [7]. However, the seed pods we examined from our site never held more than 29 seeds, whereas violet seed pods from a pair of Missouri locations typically had higher maxima of 38 to 40 seeds/pod [7]. The ecological significance of lower maxima at our study site is unknown, but it may just simply be an artifact of lower sample size (seeds counted in only 26 pods) at our site possibly missing the rare, high-seed-count pods found in Missouri. However, it appears that few birdfoot violet flowers, whether on our site or elsewhere, can maximize their reproductive output, instead setting seed quantities only 10 to 50% of their potential based on ovule numbers within the flowers [7]. This suggests that low reproductive success in birdfoot violet may contribute to rarity. Consequently, maintaining viable populations of V. pedata may be benefited by association of the violets with other species with similar flowering phenologies, that might serve to better attract and support more pollinators [3]. Additional studies (e.g., pollinator surveys, hand-pollination trials, interplanting violets with co-flowering species) at our field site would be needed to address potential causes of poor pollination success and low reproductive output per plant.
We estimated that we harvested >3000 violet seeds from our study site, and that this represented < 1% of the estimated seed production on our study prairie, likely a sustainable level of harvest during the single year of our study. Seeds have been harvested previously from natural populations of birdfoot violet and used to successfully propagate plants under controlled conditions [18]. Their laboratory experiments [18] indicate that birdfoot violet seeds need a combination of three things to maximize germination rates: removal of elaiosomes to prevent mold development, exposure to warm-dry conditions (18 to 30 °C daily cycle) for eight to 12 weeks, and stratification (i.e., exposure to cold-moist conditions; 4 °C) for eight to 12 weeks. Although elaiosome removal is likely to be tedious on such small seeds, exposures to warm-dry and cold-moist conditions are simple enough to allow seeds to experience summer and fall/winter temperatures that are important to their normal physiological development.
Whether they are grown from seed in a greenhouse and out-planted or translocated from another prairie, birdfoot violets appear to have good survival rates in native and restored prairies [16,17]. For example, birdfoot violets introduced to 20 plots in Iowa prairies displayed 3- to 4-year survival rates ranging from 55 to 92%, with those transplants also successfully reproducing during that time period, as evidenced by the presence of new plants growing within and adjacent to original planting sites [17].

6. Conclusions

Our study suggests that small prairies may have the potential to be used as a seed source for various restoration activities, at least during some years. However, due to just the single prairie surveyed during the one year of this study and the limited number of birdfoot violets monitored to assess their reproductive phenology, we need to exercise caution in interpreting our findings. We know that the population of birdfoot violet that we examined in southeastern Minnesota was restricted to a relatively small and isolated prairie habitat, and that this habitat contained a large population of violets due to high plant densities. Similarly, we know that individual violets in this population displayed low reproductive activity (flowering) and output (seed pods), but collectively the violet population produced an estimated 400,000 seeds during a single growing season, a level sufficient to support seed collection that year for use in establishing new populations of violets on nearby prairie restoration sites. However, we are unable to make any predictive statement relating to the violet population’s potential for supporting future seed collection efforts. We are unaware of possible year-to-year variability in violet densities at our study site, or whether the population we studied is typical or atypical of other populations that may exist on other dry bluff prairies within the WWMA or elsewhere within the Driftless Area. Greater effort needs to be expended toward longer-term surveys for both birdfoot violets and western regal fritillaries on dry bluff prairies within the greater Driftless Area to determine if these small remnant prairies may harbor these two species despite previous assumptions that these habitats were too small to support viable populations.
Even though a dense population of violets existed in the bluff prairie during the year we surveyed, reproductive limitation may hinder the long-term viability of this population and its usefulness as a seed source for future prairie restoration efforts. Management efforts such as enhancing pollinator habitat, planting companion species, forb-rich seeding, and/or staggered burns should be considered in the future for this site and potentially others to ensure sustainability of birdfoot violet populations. Such efforts should carry greater conservation significance due to the presence of the western regal fritillary on at least one dry bluff prairie in the WWMA.

Author Contributions

C.P., J.D., and N.D.M. developed the idea for the paper and wrote sections of the first draft. N.D.M. edited the collective first draft. C.P. and J.D. conducted all field studies and lab work. All authors have read and agreed to the published version of the manuscript.

Funding

This project did not receive any funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data available from the authors upon reasonable request.

Acknowledgments

We thank personnel from the Whitewater Wildlife Management Area for allowing us to conduct the study on the WMA. We also thank staff at Whitewater State Park, Prairie Moon Nursery, and Friends of Whitewater State Park for planning assistance and guidance. We also thank the reviewers for their excellent comments and suggestions that greatly improved the clarity and readability of the manuscript.

Conflicts of Interest

The authors declare no competing interest.

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Figure 1. Map of North America indicating the location of the study site (red star) in southeastern Minnesota and the general distribution range (green area) of the birdfoot violet (Viola pedata L.) within the eastern USA and Canada.
Figure 1. Map of North America indicating the location of the study site (red star) in southeastern Minnesota and the general distribution range (green area) of the birdfoot violet (Viola pedata L.) within the eastern USA and Canada.
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Figure 2. Aerial view of the dry bluff prairie study site (yellow star) within the Whitewater Wildlife Management Area (A), photo depicting the steepness and vegetation on the study site in April 2021 (B), and a close-up view of blossoming birdfoot violets within a 0.25 m2 plot on the study site (C).
Figure 2. Aerial view of the dry bluff prairie study site (yellow star) within the Whitewater Wildlife Management Area (A), photo depicting the steepness and vegetation on the study site in April 2021 (B), and a close-up view of blossoming birdfoot violets within a 0.25 m2 plot on the study site (C).
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Figure 3. Diagrammatic representation of the locations of birdfoot violets (numbered circles) within each of the five, 0.25 m2 plots (A through E) monitored for a 45-day period during April to June 2021.
Figure 3. Diagrammatic representation of the locations of birdfoot violets (numbered circles) within each of the five, 0.25 m2 plots (A through E) monitored for a 45-day period during April to June 2021.
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Figure 4. Diagrammatic representation of birdfoot violet densities (plants/m2) in each of 200, 1 m2 plots on the dry bluff prairie study site within the Whitewater Wildlife Management Area (A). Numbers are violet counts in each plot and colors represent differing density ranges (see legend). Columns represent uphill-downhill transects arranged across the bluff face and rows represent plots spaced at 5 m intervals along the transects. Violet densities are summarized by level across the hillslope (B). Values are means of 50 plots each and error bars are 95% confidence intervals.
Figure 4. Diagrammatic representation of birdfoot violet densities (plants/m2) in each of 200, 1 m2 plots on the dry bluff prairie study site within the Whitewater Wildlife Management Area (A). Numbers are violet counts in each plot and colors represent differing density ranges (see legend). Columns represent uphill-downhill transects arranged across the bluff face and rows represent plots spaced at 5 m intervals along the transects. Violet densities are summarized by level across the hillslope (B). Values are means of 50 plots each and error bars are 95% confidence intervals.
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Figure 5. Frequency (percent of plots) distribution of birdfoot violet plot densities (plants/m2) across the 200 plots examined on the dry bluff prairie study site within the Whitewater Wildlife Management Area, April 2021.
Figure 5. Frequency (percent of plots) distribution of birdfoot violet plot densities (plants/m2) across the 200 plots examined on the dry bluff prairie study site within the Whitewater Wildlife Management Area, April 2021.
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Figure 6. Changes in total leaf, flower, and seed pod counts for the 27 birdfoot violet plants monitored on nine dates over 45 days during April through June 2021 on the dry bluff prairie study site within the Whitewater Wildlife Management Area.
Figure 6. Changes in total leaf, flower, and seed pod counts for the 27 birdfoot violet plants monitored on nine dates over 45 days during April through June 2021 on the dry bluff prairie study site within the Whitewater Wildlife Management Area.
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Figure 7. Caterpillar of the western regal fritillary (Argynnis idalia occidentalis) observed feeding on leaves of a birdfoot violet (Viola pedata) on the dry bluff prairie study site in the Whitewater Wildlife Management Area during June 2021.
Figure 7. Caterpillar of the western regal fritillary (Argynnis idalia occidentalis) observed feeding on leaves of a birdfoot violet (Viola pedata) on the dry bluff prairie study site in the Whitewater Wildlife Management Area during June 2021.
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Table 1. Counts (means ± 95% confidence intervals, medians, ranges) of birdfoot violet leaves/plant, flowers/plant, and seed pods/plant based on repeated observations (nine) on each of 27 individual plants at Whitewater Wildlife Management Area, 21 April through 6 June 2021.
Table 1. Counts (means ± 95% confidence intervals, medians, ranges) of birdfoot violet leaves/plant, flowers/plant, and seed pods/plant based on repeated observations (nine) on each of 27 individual plants at Whitewater Wildlife Management Area, 21 April through 6 June 2021.
StatisticsLeavesFlowersSeed Pods
Mean ± 95% CI10.58 ± 2.210.66 ± 0.570.08 ± 0.15
Median900
Range3 to 350 to 90 to 3
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MDPI and ACS Style

Peterson, C.; Duffrin, J.; Mundahl, N.D. Birdfoot Violet (Viola pedata) in a Minnesota USA Dry Bluff Prairie: Population Assessment of a Preferred Host Plant of the Threatened Western Regal Fritillary Butterfly (Argynnis idalia occidentalis). Conservation 2025, 5, 58. https://doi.org/10.3390/conservation5040058

AMA Style

Peterson C, Duffrin J, Mundahl ND. Birdfoot Violet (Viola pedata) in a Minnesota USA Dry Bluff Prairie: Population Assessment of a Preferred Host Plant of the Threatened Western Regal Fritillary Butterfly (Argynnis idalia occidentalis). Conservation. 2025; 5(4):58. https://doi.org/10.3390/conservation5040058

Chicago/Turabian Style

Peterson, Chloe, James Duffrin, and Neal D. Mundahl. 2025. "Birdfoot Violet (Viola pedata) in a Minnesota USA Dry Bluff Prairie: Population Assessment of a Preferred Host Plant of the Threatened Western Regal Fritillary Butterfly (Argynnis idalia occidentalis)" Conservation 5, no. 4: 58. https://doi.org/10.3390/conservation5040058

APA Style

Peterson, C., Duffrin, J., & Mundahl, N. D. (2025). Birdfoot Violet (Viola pedata) in a Minnesota USA Dry Bluff Prairie: Population Assessment of a Preferred Host Plant of the Threatened Western Regal Fritillary Butterfly (Argynnis idalia occidentalis). Conservation, 5(4), 58. https://doi.org/10.3390/conservation5040058

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