A new scientific publication presents the results of a five-year study of the reinforced last colony of European souslik in the Natura 2000 area "Zapadna Strandzha"

18 June.2022

© Dimitar Gradinarov

A new scientific paper, published in June 2022, presents the results of five-year monitoring of a reinforced colony of European souslik (Spermophilus citellus) in the Natura 2000 protected area "Zapadna Strandzha” Special Protection Area (BG0002066), Southeastern Bulgaria.

The strengthening of the last remaining colony of this globally endangered species in Zapadna Strandzha was carried out within the BSPB LIFE project"Land for LIFE" in order to prevent the extinction of the colony due to the critically low number of sousliks. Assist. Prof Dr. Yordan Koshev and Assist. Prof Dr. Maria Kachamakova from the Institute of Biodiversity and Ecosystem Research at BAS had a leading role in the project team responsible for the activities of translocation (relocation) of sousliks, as well as in the subsequent monitoring of their adaptation in the village of Momina Tsarkva (Yambol region).

Reinforcement - these are the cases when individuals from another place are released to an existing endangered sousliks colony, was planned and carried out together with multidisciplinary research on the process of sousliks adaptation (radiotelemetry of spatial behavior, parasitological research, and analysis of stress levels ). In order to assess the success of the activities, regular annual monitoring was performed by counting the sousliks holes.

The monitoring revealed that the sousliks holes are aggregated and there is a positive correlation in their spatial distribution with the holes of the Harting's vole (Microtus hartingi) - another colonial rodent that inhabits the area. 

The first results showed the success of the activities according to the three classical evaluation criteria: individuals survived the translocation process, successfully multiplied, and initial population growth was observed - from 36 in 2017 to 280 in 2020. In 2021, however, it was registered a significant decrease in the abundance of the population - 58.5% reduction in the number of holes and 36% reduction in the area of ​​the colony. There is also a decrease in the abundance of colonies of Harting's voles.

FIG. 1: Size of the colony and souslik holes (black) and the columns of the Harting's vole in 2020 (Kachamakova et al. 2022).

A review of all the information gathered shows that abundant depression is unlikely to be due to internal parasites (helminths) (Kachamakova et al. - in press), increased levels of stress in translocation (Kachamakova et al. 2020) or other problems with behavior (Kachamakova et al. 2021).

The most likely explanation for the sudden decline in abundance is bad weather conditions - unusually high rainfall combined with relatively high temperatures in January 2021. In conclusion, the need for detailed and long-term monitoring after conservation translocations (relocation of endangered species) and careful assessment of all influencing factors before, during, and after such actions.

FIG. 2: Dynamics in the area of ​​the souslik colony near the village of Momina Tsarkva (gray columns), the number of souslik holes (red line) and the number of Harting's voles colonies (black line) during the study period (2017-2021) (Kachamakova et al., 2022).

Significant changes in numbers are characteristic of small mammals, especially rodents, and despite the observed decline in the number of souslik colonies near the village of Momina Church in 2021, the number of individuals and active holes in 2022 is twice that in 2017, before the translocation took place, and the chances of long-term survival of the colony were significantly improved.

You can read more about the study at: Kachamakova M., Y. Koshev, D.-L. Rammou, S. Spasov. 2022. Rise and fall: Results of a multidisciplinary study and 5-year long monitoring of conservation translocation of the European ground squirrel. - Biodiversity Data Journal 10: e83321. https://doi.org/10.3897/BDJ.10.e83321

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