Whereas European ground squirrels (Spermophilus citellus) do not utilize food caches during hibernation, it has occasionally been reported that they store food during the active season. Recent evidence for S. citellus maintaining food stores in summer arose during the long-term ecological supervision of a construction project in Vienna, Austria. From the onset of the project in 2012, ground squirrels were observed to forage on tubers of the tuberous vetchling (Lathyrus tuberosus). During the preparation of a building plot in July 2016, a cavity containing 380g of tubers of L. tuberosus was excavated by a digger when removing the upper 30 cm soil layer. When the construction area was expanded in July 2017, a ground squirrel repeatedly inspected a burrow on a future building plot, once carrying a tuber to the burrow. To examine if the burrow was vacant, it was stripped by layer, revealing a cache of 290g tubers in a blind-ending tunnel at a depth of about 90 cm. The structure consisted of one chamber without nesting material, and one tunnel containing the cache. We conclude that the burrow may have served as a hideout facilitating food intake while avoiding predation and other adverse external conditions.

AbstractCricetus cricetus (Linnaeus, 1758) is a medium-sized cricetid commonly called the common hamster. A sexually dimorphic rodent of unique coloration with robust body, blunt head, short legs, and rudimentary tail, it is the largest hamster and the only species in the genus Cricetus. It is easily recognizable by a color pattern of contrasting dark and light areas. Because its distribution extends from northwestern Europe to eastern China across 5,500 km of low altitude agricultural land, steppe, and forest steppe, the frequently used term European hamster is misleading. Both geographic range and relative abundance started declining in the 1960s on the western edge of its distribution, and now C. cricetus is protected by the Bern Convention and the Fauna-Flora-Habitats Directives.

Genetic diversity is of paramount importance for individual fitness and evolutionary potential of populations. For conservation planning it is crucial to know how genetically diverse a species is and what factors may explain variation of genetic diversity among populations. Our aim was to evaluate the effects of landscape history, ecological isolation, and local population size on allelic richness of local populations in European ground squirrels (Spermophilus citellus). We genotyped 144 individuals from nine local populations collected in two neighbouring regions with decades of different landscape history. We assessed allelic richness, ecological isolation and local population size by eleven polymorphic microsatellites, the isolation index of Rodriguez and Delibes, and standardised counts of burrows openings, respectively. Statistical models indicated a strong effect of landscape history on allelic richness of local populations. Ecological isolation of local populations apparently played only a marginal role, and local population size was an unimportant factor. Our modelling results highlight the dominant role of landscape history for the genetic diversity of S. citellus. The strong landscape history effect encountered presently includes a different regionspecific socio-economic development due to distinct agricultural systems in the two regions, especially after World War II. Levels of ecological isolation of local populations have diverged in an extent too small to explain variation of local allelic richness. The lack of a significant effect of local population size suggests that census sizes of the populations studied are all not critically low. Moreover, census and estimated effective population sizes were not closely related. Establishing corridors or translocating S. citellus in the species' historical range should be encouraged to promote gene flow between local populations and counteract the loss of genetic diversity by drift, provided that no conflicting factors (ecological, epidemiological, etc.) exist.

Spermophilus citellus (Linnaeus, 1766) is a medium-sized sciurid commonly called the European ground squirrel. The species inhabits grasslands in central and southeastern Europe on a range from short-grass steppes to meadow orchards, and from sea level to an elevation of 2,500 m. These squirrels live in colonies and construct burrows used for hibernation, reproduction, refuge, and resting. Due to serious declines in many portions of its range, the species is listed as "Vulnerable" by the International Union for Conservation of Nature and Natural Resources. It is also protected by the Bern Convention (Appendix II), and the European Union Habitats and Species Directive (Annexes II and IV).

Abstract Following the expansion of agriculture in the Neolithic period, the common hamster has spread throughout Europe, and occurred abundantly until the recent past. However, in the last 45 years, populations declined markedly, partly attributable to urbanization and to major changes in agricultural practices. As a result, the species has been considered endangered at international levels as well as in most European countries. At the same time, the species has established populations in large Central and Eastern-European cities such as Vienna (Austria), Simferopol (Ukraine) and Nalchik (Russia), where it inhabits green spaces such as parks, gardens, embankments and buffer strips. In an attempt to reveal factors enabling hamsters to cope with urban environments, we reviewed historical data and habitat conditions of several urban hamster populations. We suggest that supplemental food resources and reduced predation pressure were the main factors promoting urban occurrence of common hamsters in the last 30 years. Its notable adaptability may be associated with higher stress resilience, ecological opportunism, polyphagy and higher fertility compared to species relying on non-urban habitats. The phenomenon of synurbization implies coexistence of wildlife and our urban civilization, but at the same time conflicting interests in conservation and urban development. Thus, the common hamster might serve as a model species for efficient mitigation and compensation concepts in urbanism and spatial planning.

The European ground squirrel ( Spermophilus citellus ) is endangered and in decline. Populations are increasingly fragmented, and only a coordinated conservation effort at the European level may guarantee its long-term survival. To obtain a general population genetic picture on a larger geographic scale, we screened 117 individuals from seven local populations in Hungary, Romania, and Austria for allelic variation at eleven microsatellite loci. We found a high (23.4%) proportion of private alleles, and a moderate to some what elevated level (15.27%)of partitioning of genetic diversity among populations, compared to that found in many other terrestrial mammals. Genetic variability was significantly higher than in earlier studied Czech populations that are considered genetically depleted, but significantly lower than in undisturbed populations of S. suslicus and S. brunneus , that are similar to the European ground squirrel in their ecological requirements, reproductive biology, and social organization. Genetic diversity was also lower than in most presumably “undisturbed” populations of other Sciurid species. This, together with the observed level and pattern of genetic differentiation among populations, such as no significant increase of genetic differentiation with geographic distance and similar variance of genetic differentiation between populations independent of geographic distance, indicated the prevalence of relatively strong drift effects for all populations. A Bayesian STRUCTURE analysis and a factorial correspondence analysis concordantly revealed a fairly complex genetic composition of local populations, but no major geographic trend in the pattern of the genetic composition. Overall, the results suggest disintegration of local colonies that might earlier have been more connected genetically. The STRUCTURE analysis also suggested anthropogenic translocations among single Hungarian populations. Our data on genetic diversity and its distribution do not object to such conservation measures. Translocation of individuals particularly from nearby populations may increase the chances of survival of small and isolated populations and counteract inbreeding at low densities.

In some hibernating species, an extended euthermic period before spring emergence has been reported during which testicular maturation occurred. In this study, we investigated whether male European ground squirrels Spermophilus citellus (Linnaeus, 1766) develop scrotal testes before or after the termination of hibernation. The course of testis development and testosterone concentrations were examined in young-of-year male ground squirrels (n = 4) before, during, and after their first hibernation. In the environmental chamber, all animals showed regular hibernation patterns with decreasing torpor bout lengths prior to the end of hibernation. Four weeks before hibernation ended, testosterone levels were elevated during spontaneous arousals. Testosterone concentrations peaked during the first 2 months post heterothermy and decreased thereafter. In 2 experimental males, testes descended from the inguinal region into the scrotum shortly before the end of heterothermy. The state of testis development and testosterone secretion corresponded to that found in semi-free-living males at spring emergence. Testis size increased in active animals to maximum widths during weeks 3 and 4 post heterothermy. Scrotal skin pigmentation was absent until heterothermy ended and developed during the first month thereafter. The data suggest that male S. citellus do not need a pre-emergence euthermic period for reproductive development.

In seasonally breeding mammals, in particular hibernators, reproduction underlies severe energetic and temporal constraints to enable the allocation of sufficient body fat reserves before winter. Thus, the timing of conception in spring can be crucial in terms of reproductive success. This study investigates follicular development in European ground squirrels (Spermophilus citellus) in three phases of the annual cycle: at vernal emergence, after weaning the offspring and shortly before hibernation. The animals were kept in outdoor enclosures within the natural habitat of the species. They were captured in weekly intervals, weighed and reproductive status was determined. Unilateral ovariectomy was scheduled such that the three periods were sampled. Numbers and diameters of tertiary follicles (TF) and corpora lutea (CL) in each ovary were determined, and plasma oestradiol and progesterone levels were analysed. The highest numbers of TF, including Graafian follicles, were found in ovaries at vernal emergence. During post-lactation, the number of TF was lower and active CL appeared in the investigated ovaries. Shortly before hibernation, active CL were present, but luteolysis had started in some individuals. Both oestradiol and progesterone secretion peaked after the termination of lactation and decreased before hibernation. The results demonstrate a second oestrus cycle in European ground squirrels after weaning, including an active luteal phase. This non-reproductive oestrus cycle with its endocrine output is an intriguing phenomenon. It may positively affect both prehibernatory fattening and reproduction in the subsequent season.

Most hibernating animals are thought to be monoestrous because reproductive activity is subject to strong time constraints. In previous studies, female European ground squirrels (Spermophilus citellus) turned out to have elevated oestradiol levels during late lactation and after weaning, indicating ovarian activity during summer. Therefore, we monitored vaginal cytology, endocrine changes, and vulval development in semi-free-living female European ground squirrels throughout one active season. Vaginal oestrus, defined by the predominance of cornified cells in smear samples, was found during the mating period shortly after vernal emergence. This phase was followed by metoestrus, characterised by the appearance of leukocytes, and a subsequent anoestrous phase. During weaning or postlactation, a second vaginal oestrus was documented in all experimental females, again followed by a metoestrous and an anoestrous phase lasting until hibernation. In line with the second vaginal oestrus, plasma oestradiol concentrations peaked during postlactation. Progesterone levels were elevated from gestation to postlactation, and titres were marginally higher during vaginal oestrus in summer than in spring. Vulval swelling was more pronounced during the first than the second vaginal oestrus. The second oestrous cycle was non-reproductive, as males were sexually inactive with regressed testes during summer. We assume that the second oestrous cycle and the accompanying endocrine changes have beneficial effects on prehibernatory fattening and reproductive performance in the subsequent season. This might allow females to become oestrous immediately after emergence from hibernation in spring.

In European ground squirrels ( Spermophilus citellus ) as in other obligate hibernators, physiological processes underlie strict time constraints. Especially for the juveniles growth and prehibernatory fattening are temporally very limited. The aim of this study was to determine the effects of specific nutritional factors on development in juvenile males. Male ground squirrels were investigated for a 7-week period starting at natal emergence. Individuals were assigned to 1 of 3 experimental groups and were provided with a diet either high in proteins or polyunsaturated fatty acids (PUFAs). The third group was used as a control and was fed with a standard rat diet. Food quality affected growth in that males of the high-protein group had significantly larger head lengths in week 4, 5, and 6 after natal emergence than those of the other 2 groups. However, body mass did not differ significantly between the groups. All juvenile males showed an increase in plasma testosterone levels from week 1–2 to week 3–4 post-emergence, thereafter testosterone secretion remained stable until week 5–6. The daily testosterone increase after the first 2 weeks was significantly higher in the PUFA group compared to the other 2 groups. The results underline the importance of diet composition for growth rates and the timing of gonadal activation during early development in this species.

In the course of a long-term study on reproductive physiology and behaviour in female European ground squirrels (Spermophilus citellus) we investigated interactions among reproductive timing, maternal effort and hibernation. To gain information on the state of follicular development shortly before hibernation, histological investigations of ovaries were carried out. To collect the ovaries, unilateral ovariectomy was chosen as the least invasive method. The aim of this study was to monitor patterns of hormone secretion, behavioural parameters and reproductive output in females after unilateral ovariectomy, and compare them with intact individuals to assess potential effects of the treatment. Reproductive performance including duration of gestation and lactation, litter size, and offspring mass at natal emergence were similar in treated and untreated individuals. Before weaning, plasma estradiol levels were higher in the hemicastrated group than in intact females. Progesterone concentrations tended to be lower in unilaterally ovariectomized females during gestation and postlactation. In both groups we measured cortisol metabolites in fecal samples to estimate basal adrenal activity. Untreated individuals had significantly higher cortisol levels than hemicastrated females during lactation. In all other phases no significant differences in patterns of cortisol excretion were found between the two groups. Prehibernatory body-mass did not differ between treated and untreated females. These results indicate that unilateral ovariectomy had no significant negative effects on reproductive timing and output in female European ground squirrels. Compensatory activity of the remaining ovary does occur, concerning estradiol secretion even a kind of overcompensation was reported. These elevated estradiol levels in unilaterally ovariectomized females could play a role in limiting the degree of follicular compensation.

Daily aboveground activity of European ground squirrels (Spermophilus citellus) in their natural habitat was recorded with a visual scanning procedure during the active seasons of 1992 and 1993. Activity patterns were analyzed with respect to time of year and to the animal's reproductive state. Aboveground activity started on average 3.9 h (SD 0.6 h, n = 37 days) after civil twilight at dawn and ended on average 3.2 h (SD 0.9 h, n = 37 days) before civil twilight at dusk. Between onset and offset of activity, 54% was spent aboveground, of which 73% was spent foraging. Activity patterns were influenced by photoperiod, rainfall, and by reproductive state. During mating, reproductively active males started activity earlier than females and reproductively inactive males. For females, time spent foraging was high during lactation. The midpoint of daily activity was at 12:16 h (SD 0.37 h, n = 37 days). Activity patterns of European ground squirrels thus appear robustly positioned in the middle of the photoperiod.

We monitored European ground squirrels (Spermophilus citellus) in a recreation area near Vienna, Austria, over a 7-year period to follow their population dynamics. Data were obtained by mark-recapture and daily checklists in an attempt to track the fates of individuals present in a defined area. Abundance of nonjuveniles present in spring decreased from 56.0 individuals/ha in 1992 to 6.3 individuals/ha in 1998. Litter size and yearling-male reproduction were inversely related to density, whereas immigration, juvenile survival, and proportions of nonjuvenile males exhibited a positive relationship. We conclude that the study population had been a dispersal sink and that ceasing immigration combined with poor local survival caused the population to crash. The temporal coincidence of these 2 effects indicates an extrinsic factor acting both on residents and potential immigrants.

European ground squirrels typically inhabit dry grasslands throughout central and south-eastern Europe. Over the past decades, the species increasingly utilises anthropogenically shaped areas. During a 7-year field study on a population in a semi-urban habitat near Vienna, Austria, we monitored a 5.9-fold decrease in ground-squirrel abundance, with high densities having been maintained by immigration. The decline occurred parallel to an escalating urbanisation of the surroundings. A survey concerning the former dispersion of squirrels indicated an increase in population size during the late 1970s, after the region had been drained. Our findings suggest that improved river control of the Danube had ameliorated a sub-optimal habitat, which enhanced the formation of a dispersal sink. After several years of high population levels, abundance decreased, most likely due to anthropogenically promoted landscape fragmentation and habitat degradation. The results of our study support the assumption that artificially induced environmental changes may be crucial for the persistence of small-mammal populations at the edge of their geographic range.

This field study was aimed at examining hypothalamic involvement in the behavioral changes of male European ground squirrels (Spermophilus citellus) before, during, and after the mating season. The effects of exogenous gonadotropin-releasing hormone (GnRH) application on androgen secretion and behavioral patterns were investigated. Animals were captured, bled, and injected intramuscularly with 40 ng/100 g of GnRH. A second plasma sample was collected 40 min after the treatment to document changes in testosterone secretion. Behavioral parameters such as intra-sexual aggression, scent marking, and home range size were compared on the days before and after the stimulation. In the first two phases, before female emergence and during mating, GnRH-injection caused increases in plasma testosterone. In the post-mating phase, initial plasma testosterone levels had decreased and no elevation could be induced. Sham treatment of controls had no effect in any phase. Conditional parameters like emergence body mass and testicular size covaried with androgen increases only in the pre-mating period. Behavioral changes after GnRH administration occurred during the pre-mating period. Intra-sexual aggression, scent marking, and home range size increased significantly in experimental individuals. Later, during mating and post-mating, we found no behavioral changes associated with the GnRH treatment or the testosterone increase. The results demonstrate changes in the endocrine and behavioral sensitivity to GnRH application, according to the phases of the active season. An exogenous pulse of GnRH can apparently release behavior in male European ground squirrels, which is normally context dependent with the emergence of females.

In European ground squirrels Spermophilus citellus as in many ground squirrel species, late born litters are composed of fewer young than early born litters. Two alternative though not mutually exclusive hypotheses may explain this seasonal pattern of change in litter size. On the one hand, the production of few large young late in the season may be an adaptation to time limitations on the offspring, that have to complete growth and fattening prior to hibernation. Then one would expect a trade‐off between offspring number and size as the breeding season progresses. At its extreme, this hypothesis would predict that total maternal effort should be equal independent of litter size. Alternatively, litter size may be determined by physiological limitations on the mother, in that highly constrained mothers breed later and produce smaller litters. Then one would expect reduced overall maternal effort in highly constrained mothers of smaller litters. In this case, a trade‐off between litter size and offspring size would not be expected. We found that total maternal effort in terms of gestation length and the duration of lactation increased with increasing litter size, thus supporting the second hypothesis. Lactation was not terminated at natal emergence. It extended a relatively long period of time beyond the time of first litter emergence depending on litter size. During prolonged lactation, individual young of large litters made up body mass to young of small litters. As a consequence, juvenile weaning body mass was unaffected by litter size although offspring body mass at natal emergence was inversely related to litter size. This additional weight gain in young of large litters compensated for initial survival disadvantages and presumably affected fecundity at yearling age.