2023 field survey documents establishment of transferred Violet Copper population in the Šumava Mountains

A 2023 field survey found that the Violet Copper butterfly, Lycaena helle, had established a substantial population in the Šumava Mountains of Czechia following its transfer from the Austrian Alps in 2002. Researchers recorded the species in 71 of 212 surveyed grassland and fenland patches, covering 66.6 hectares of suitable habitat within an overall distribution range of approximately 4.5 square kilometres. The study assessed the distribution and habitat associations of the introduced population two decades after establishment.

The transfer involved 35 adults—two males and 33 females—collected in June 2002 from a mountain population in the Türnitz Alps and transferred to Nové Údolí in Šumava National Park. The release site was approximately 160 aerial kilometres from the source and contained grasslands and fens in which the butterfly’s principal larval host, Bistorta officinalis, was dominant. Butterflies remained near the release patches for three years before expanding into adjacent grasslands. A mark-recapture study in 2011 and 2012 estimated about 110 adults in three hectares of patches and found records up to 900 metres from the release point.

For the 2023 study, the authors surveyed all identifiable grassland and fenland patches around Nové Údolí, along the Studená Vltava River, beside Hraniční potok, near the Czech-German border and around Stožec and Černý Kříž. Surveys were conducted from June 1 to 10 during suitable butterfly activity. Each of the 212 patches, with a combined area of 285.7 hectares, was visited once and surveyed along a zigzag route. Presence was recorded as present or absent, while abundance was assigned to an ordinal scale from one individual to more than 20.

During the survey, the authors made 557 observations of L. helle. The butterfly was concentrated around the former Nové Údolí village, along the Studená Vltava River and near Spálený luh bog. Records became less frequent northward, and the most distant observation was 4,210 aerial metres northwest of the release point. The species was not detected in the surveyed fenlands around Stožec or Černý Kříž, which were separated from the occupied range by extensive mature spruce forests.

Principal-component analysis associated butterfly presence and abundance with wet, relatively impenetrable and unmanaged grasslands, generally on flat terrain with closed edges and substantial Bistorta cover. Regression models produced similar associations. Presence and abundance generally increased with wetness, closed habitat edges and host-plant cover, and declined with active management, slope, cloud cover and wind. Bistorta officinalis covered a mean 49.6% of occupied patches, compared with 23.4% of unoccupied patches, although the observed values varied substantially among patches.

The habitat associations were consistent with reports from other populations of L. helle in Central and Western Europe. The butterfly was most closely associated with waterlogged grasslands in an advanced stage of succession, where B. officinalis remained abundant but woody encroachment had not eliminated the host plant. Regular mowing or grazing tended to reduce the host plant, whereas complete abandonment could allow taller grasses, sedges and woody vegetation to dominate. The survey therefore identified a narrow habitat window rather than a simple association with either management or abandonment.

The 2023 observations do not directly establish the total adult population because abundance was scored ordinally rather than counted at every patch. The authors extrapolated an estimate of approximately 2,400 adults by applying the earlier 2011–2012 estimate from a smaller, high-density area to the 66.6 hectares occupied in 2023. They explicitly cautioned that this figure may be inflated because the earlier mark-recapture survey sampled dense patches. The more direct evidence was the recording of more than 500 individuals during the 2023 survey and the substantially larger occupied habitat area than in the earlier assessment.

The occupied range expanded from a most distant record of 900 metres after the first decade to 4,210 metres after two decades. This corresponds to an average expansion rate of 0.1 kilometres per year during the first decade and 0.2 kilometres per year over the full 20 years. The authors estimated that the Šumava population expanded more slowly than translocated L. helle populations in France, where rates of 0.52 kilometres per year in Morvan and 0.45 kilometres per year in Forez were reported. Available genetic-heterozygosity measurements did not support genetic impoverishment as the explanation for the slower expansion.

This observational field study has several bounded limitations. Each patch was visited only once during the species’ short adult flight period, so variation among survey dates and weather conditions could affect presence and ordinal abundance estimates. The study covered a defined landscape around the release area rather than the species’ complete European distribution, and it did not directly measure total adult numbers in 2023. Its findings indicate that the transferred population was established and expanding across suitable grasslands, while also showing that it had not crossed the surrounding continuous forest barriers during the study period.

Subject of Research: Field assessment of the distribution and habitat associations of a translocated Violet Copper population in the Šumava Mountains

Article Title: Population status of the highly endangered Lycaena helle ( Papilionoidea , Lycaenidae ) in the Šumava Mts. two decades after establishment

Article References: Peškařová, T., Pavlíčko, A., Kuras, T., Fric, Z. F., & Konvička, M. (2024). Population status of the highly endangered Lycaena helle (Papilionoidea, Lycaenidae) in the Šumava Mts. two decades after establishment. Nota Lepidopterologica, 47, 171-186. https://doi.org/10.3897/nl.47.126025

Image Credits: AI Generated

DOI: 10.3897/nl.47.126025

Keywords: Violet Copper, Lycaena helle, species translocation, Šumava Mountains, butterfly conservation, habitat selection, grassland management, population monitoring, Czech Republic, Population, status, highly