Environmental factors and intrinsic processes affecting habitat use of European ground squirrels (Spermophilus citellus): putting science into conservation practice

Abstract

In my Ph.D. thesis I investigated a few factors that influence the habitat use of the European ground squirrel (Spermophilus citellus; as EGS hereafter) and the Gunnison’s prairie dog (Cynomys gunnisoni; as GPD hereafter), two ecologically similar ground dwelling sciurids. I attempted to show the importance of a few extrinsic and intrinsic mechanisms by which the association between the habitat and ground squirrels is maintained. EGS show a strong preference for fresh Festuca pseudovina. Insulation property of the squirrels’ fresh grass nests was superior to nests constructed from dry grass only. Our results suggest that squirrels may rely on dominant xeromorphic fescues of dry meadows because of their importance to nest building. Consequently, it can be assumed that populations will expand to unoccupied areas and survive for longer-time and reintroductions will be successful if the habitat is characterized by fescues. GPD use mounds for vigilance and it increases with taller vegetation. Vigilance is more frequent and directed outward by individuals on the periphery than those in the interior of the colony. GPD we excavates about 6.5-16.6 m3/ ha/ year, so they can be considered as ecosystem-engineers indeed. It is possible to estimate volume of burrows with our calculation method by measuring the amount of subsoil displaced in the mound. Information on volume of burrows can be applied to monitor how the size of natural or artificial burrows changes. Results of translocation experiments showed that release time should correspond to the morning activity peak of EGS, the artificial burrow with retention cap prevents panic reactions, and angled artificial burrows and medium-height grass (18 cm ± 12 SD) favour translocation success in the critical period after release. Genetic diversity of EGS populations from Hungary, Romania and Austria was higher than that of the Czech populations but all studied populations have relatively low heterozygosity in comparison with other sciurids. Nevertheless, and perhaps as a result of simultaneously acting factors the genetic diversity of populations of neighbouring regions can differ significantly. To summarize, ground squirrels are sensitive to changes in environmental factors, facilitating fluctuations in population size. Ecological sensitivity, interacting with “scramble-competition polygyny”, implies a more serious threat to the persistence of the species than possible negative effects of translocations as regards the genetic aspects. This notion is illustrated by the ongoing, rising isolation and disappearance of colonies.