Souslik
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Increase number and size of protected souslik colonies
Data collection in progress
Iron Curtain to Green Belt
Bulgaria
Problem: The project landscape is home to important populations of threatened raptors, for which small mammals, and particularly the European souslik, are key prey species. However, souslik numbers are under threat, primarily due to loss of their preferred habitats, a short grazed grassland. The conversion of pastures to arable agriculture and abandonment of grazing are leading to reductions in souslik and other small mammals numbers.
Action: The project is buying areas of grassland known to contain colonies of souslik and working with farmers to ensure suitable grazing intensities are maintained, to improve souslik and other small mammals’ habitats.
Indicator: The success of souslik habitat protections is being measured by recording the number and size of land plots containing souslik colonies that are purchased and the density of active souslik holes per hectare in these colonies. The presence and abundance of other four other small mammal prey will also be recorded at these sites.
Photo: Svetoslav Spasov
Aerial image of preferred souslik habitat. Photo: Dimitar Gradinarov
Methods
Data on the sites and their areas that have been purchased and protected will be taken from land transaction records. Agreements with farmers for sustainable grazing in these areas will further provide data on where the good quality souslik habitats are located.
The health of the souslik colonies in these sites will then be measured by counting the number of active holes on all sites to provide an assessment of their relative abundance. Surveys are conducted in spring or summer by walking repeatable transects, spaced 10-15 m apart, that are situated to achieve full coverage of each land plot. Active holes are easily recognisable by signs of digging, excrement and pathways to the hole. Once all active holes in plot are recorded, the relative density will be calculated.
The presence of four other small mammals species – Harting’s vole (Microtus hartingi), lesser blind mole-rat (Spalax leucodon), European mole (Talpa europaea) and European hare (Lepus europaeus) – will be recorded at the same time. Active holes, excrement and direct observation of individuals will be recorded. Relative abundance will also be estimated for these species, except for European hare where abundance cannot be assessed using this method.
Results
The baseline at the start of the project (2022) was 15 land plots that were purchased and protected with souslik colonies within the project area, totalling 20 ha .
In 2023, 61 land plots, with a total area of 53 ha, were purchased and protected. An initial survey of souslik colonies in 2023 found an average of 60 active holes/ha (range 10-110 active holes/ha).
The project team are continuing to collect data on the other small mammal species and at the additional land plots that have been purchased. We will update this page once more information becomes available.
References
Data collection methodology is part of the National Biodiversity Monitoring System (NBMS), run by the Executive Environment Agency (ExEA), Ministry of Environment and Waters https://eea.government.bg/en
Link to European souslik monitoring methodology, in Bulgarian:
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