Vipera berus (Linneaus 1758)

Elmberg, Johan, 2023, Amphibians and reptiles in North Sweden: distribution, habitat affinities, and abundance (Classes: Amphibia and Reptilia), Zootaxa 5301 (3), pp. 301-335 : 322-324

Adder Vipera berus (Linneaus 1758)

Distribution ( Figure 10 ). Included records from Artportalen (N=1250): all reports have been included. Any confusion between melanistic Vipera berus and Natrix natrix would not affect the distribution pattern.

Common and widespread in the Southern and Middle Boreal. Widespread and locally common in the Northern Boreal, where often found in areas of varied topography with south-facing slopes that offer early snowmelt and dependable hibernacula (Andersson 2003; Figure 20 ). Scattered observations have been made in the Subalpine and Low-Alpine zones ( Curry-Lindahl 1975; Frislid & Semb-Johansson 1981; Elmberg 1995).

The highest reported occurrences show a slightly decreasing altitude from south to north: 940 m in Härjedalen (Flatruet), 900 m in Jämtland (Oviksfjällen), 720 m in Lycksele lappmark (Kraipe), but 820 m in Lule lappmark (Aktse). Most of these concern south-facing sites in the upper Subalpine zone, but also above treeline in the Low-Alpine zone. In the upper reaches of the river Lilla Luleälv (Lule lappmark) there are many records in the Aktse and Tarradalen areas (e.g., Cederberg 1974), suggesting widespread occurrence in the Subalpine zone there.

Widespread and locally abundant on many offshore islands along much of the Baltic coast of North Sweden ( Figure 10 ), as is the case across the sea in Finland ( Terhivuo 1981). An illustrative example is the Holmön archipelago in Västerbotten, where this species is abundant on islands> 10 km from the mainland. This implies high dispersal capacity over brackish water.

There are no indications of large-scale changes in distribution over the last 50 years.

Habitat and movements. Males typically emerge from hibernation two weeks before females. Mating occurs near the hibernaculum, after which snakes disperse to summer habitats. The latter are largely the same as those of Zootoca vivipara : forest edges, forest clearings, stony slopes, rock outcrops, shrubbery, and shores of lakes, rivers, and the sea ( Figure 12 ). In the vast interior of North Sweden summer habitats also include margins of bogs and mires ( Figure 14 ). Areas providing a combination of basking sites and hiding places are favored. Anthropogenic habitats are widely used, too, for example clearings under powerlines, clear-cuts, edges of fields and meadows, and stone walls ( Figures 13 , 19 ). Very rarely found in closed forest, but sometimes in mature pine forest with natural gaps and clearings. It also occurs regularly in dense Juniperus communis thickets and in tall grass, where prey animals are likely to be found.

There are not any telemetry data available from North Sweden, but judging from field observations Vipera berus appears to be more mobile in summer than are Zootoca vivipara and Anguis fragilis . However, Andersson (2003) reported from the Northern Boreal that pregnant females may remain close to the hibernaculum throughout summer. The distance from summer habitats to hibernation sites can be up to 2 km (Andersson 2003), a journey during which Vipera berus can be found in other habitats.

Hibernation usually occurs in open south-facing locations with abundant crevices and underground access. Typical sites are talus slopes, stony moraine ridges (cf.Andersson 2003) and screes in the forest landscape ( Figure 20 ), but also cairns if big and deep enough. Good hibernation sites are always well-drained and can attract individuals from a large surrounding area. There are reports from North Sweden that a single hibernaculum can host hundreds of individuals ( Frislid & Semb-Johansson 1981).

Abundance estimates and trends. There are not any published abundance data, but estimates based on extensive field work in the Umeå area (Västerbotten) 1975–1994 run in the neighborhood of 50– 100 adults /km 2 ( Elmberg , unpublished). A mark-recapture study on the far offshore island Stora Fjäderägg (Västerbotten; 63 o 48’N, 21 o 00’E; area ca 170 hectares) suggests an average abundance of ca. 0.6 adults/hectare (60/km 2) (Stefan Andersson, unpublished). However, studies by Stefan Andersson on the mainland suggest that abundance estimates for larger areas are particularly difficult to make in this species; adults occur within a certain radius of hibernacula, but between the latter there may be large areas of good summer habitat more or less devoid of adders.

There are not any true monitoring data for any period of the last 50 years, but recurrent visits to known sites of occurrence in southern Västerbotten indicate a steady and significant drop in abundance from the late 1970’s to the present day (Elmberg, unpublished).

Figures

FIGURE 10. Distribution of Vipera berus in North Sweden. Colored parts of the Baltic in Ångermanland, Västerbotten, and Norrbotten represent areas with widespread occurrence on offshore islands. Triangles at sea in Medelpad and Hälsingland represent more singular offshore occurrences. Question marks denote areas where the western range limit is poorly known.

FIGURE 12. Ongoing post-glacial land uplift creates open habitats along the Baltic coast of North Sweden. Rock pools (foreground) serve as breeding sites for Rana temporaria and Bufo bufo, occasionally also for Lissotriton vulgaris. Brushy areas along the forest edge (background) are typical summer habitat for Zootoca vivipara and Vipera berus. Tjäruskär, Ångermanland, Middle Boreal region. Photo: Johan Elmberg.

FIGURE 13. Recently abandoned hayfields are prime summer habitat for Rana temporaria, R. arvalis, Bufo bufo, Anguis fragilis, and Vipera berus. The forest edge in the background is typical habitat also for Zootoca vivipara. Baggböle, Västerbotten, Middle Boreal region. Photo: Johan Elmberg.

FIGURE 14. Vast areas of North Sweden’s interior are covered by level open bogs with permanent water. Rana temporaria, R. arvalis, and Bufo bufo breed in the pool depressions (foreground) and come ashore to forage in grassy areas in summer. More elevated and drier string parts of the bogs offer protective vegetation and summer habitat för Zootoca vivipara and Vipera berus. Photo: Jonas Grahn.

FIGURE 19. Clear-cuts offer summer habitat for Zootoca vivipara, Anguis fragilis, and Vipera berus for a decade or so until planted conifers grow tall enough to shade the ground. Robertsfors, Västerbotten, Middle Boreal region. Photo: Johan Elmberg.

FIGURE 20. Talus slopes and screes provide communal hibernation sites for Vipera berus, offering frost-free conditions also in case of early winter weather with little insulating snow cover. Such sites invariably face SW–SE and have early snowmelt that permits earlier spring emergence than in surrounding areas. Mating usually takes place here, after which vipers disperse to summer habitats visible in the background. This picture is from one of the northernmost known hibernation sites in Sweden at 68oN. Etnoluhtinvaara, Torne lappmark, Northern Boreal region. Photo: Stefan Andersson.