Abstract
The regal fritillary (“regal”) (Speyeria idalia) is endangered in Wisconsin, USA, and declining and at risk range-wide. During 1988–2015, we surveyed 24 known regal sites and >100 areas of potential habitat in Wisconsin. We recorded 9037 individuals in 742.7 km on the peak survey per year at occupied sites. At six sites surveyed over 5–25 years, we found regal fritillaries in only one year, mostly in the latter half of the study. The three populations in the state with more favorable trends than the median had a never-burned refugium and/or infrequent fire management. They also all had substantial amounts of grazing, haying, and/or mowing managements. Sites with trends below the regional median trend had frequent or moderate fire management, and either a diminishing never-burned refugium or none at all. Regal populations at sites with ≤15 ha of grassland have become undetectable. Nonetheless, Hogback, a slightly larger than 15 ha site, had the most favorable trend, a significant increase. Nearly all Wisconsin Regal populations known before 1990 declined to consistent non-findability, even though these were conserved sites. More favorable trends at more recently discovered populations may be attributable to species-specific habitat management protocols implemented in the 1990s. Two sites with better than median long-term trends represent the longest consistent land ownership of known Regal populations in the state. This wide range of population outcomes illustrates both the need for long-term monitoring and the challenges of explaining the outcomes. Despite evidence of increasing Regal dispersal, this species remains very localized, indicating the unsuitability of the wider landscape as regal habitat. The number of significantly declining or no longer detectable populations in Wisconsin indicates an ever more adverse landscape for this species. Sites will need to have habitat characteristics that are ever more optimal in a wide range of climatic conditions for Regal populations to persist.
Highlights
Surveying and monitoring are necessary components of conservation programs for rare or declining butterfly species [1,2]
The clustering of most of these sporadic records in and adjoining counties with regal populations (Figure 1) supports that these sporadic records may be symptomatic of dispersal from a relatively near population
The wide range of population outcomes documented in this study illustrates both the need and the challenge of anticipating future effects of climatic variation and site-specific habitat characteristics and their landscape context
Summary
Surveying and monitoring are necessary components of conservation programs for rare or declining butterfly species [1,2]. Our study species is the regal fritillary (Speyeria idalia) (Lepidoptera: Nymphalidae), referred to as “regal” or “regals” here. This butterfly is listed under state regulations as endangered in Wisconsin [8]. It is categorized as threatened, endangered, or extirpated in various other states and Canadian provinces, and is currently under review by the U.S Fish and Wildlife Service for federal listing [9]
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