Global and European regional assessment: Vulnerable (VU)
EU 27 regional assessment: Vulnerable (VU)

In 2015, the Garden Dormouse occupied 49% of its 1978 geographical range and 67% of its 2008 range. On top of this, it has been likely extirpated from several countries. Therefore, the species is assessed as Vulnerable (A2c) both globally and for the EU27 region, as it can be inferred that the population has been reduced by more than 30% in the last 10 years (2012-2022). The causes of decline are not fully understood, and there is a clear need for further research and conservation efforts.

The Garden Dormouse (Eliomys quercinus) is endemic to Europe, where it historically occurred from Portugal to the Urals (Russia) and from Finland to southern Italy. It is now primarily confined to western Europe, with only scattered populations in the east. Its altitudinal range is from sea level to 2,000 m.

The species is considered extinct in Lithuania, Finland, and Slovakia (Juškaitis 2003, Bertolino 2017), probably in Belarus (the last two records in 1962 and 1996, Bertolino 2017), Latvia (no records since the mid-1990s, despite widespread monitoring, Pilāts 2022), Estonia (last record in 1986, Timm and Maran 2020), and present with single populations in the Netherlands, Poland (the last certain record in 1960s from Zawoja, vicinity of Babia Gòra, Cichocki et al. 2022), and Slovenia (only one record, Kryštufek 2003). The species is rare and localised in Austria (Spitzenberger 2002) and Croatia and is in regression in Germany (Meinig and Büchner 2012), Flanders (Belgium), and Czechia (Andera 1994). Museum and literature records from Romania (Hegyeli 2022) and Ukraine (Misthta 2022) are questionable. Old records of alleged Garden Dormouse in Romania were misinterpreted, and presently, there are no museum specimens nor publications with photos, measurements or detailed descriptions of individuals confirming the present or past presence of the species in the country (Hgyeli 2022). Most of the specimens in the Ukrainian museums were attributed to the Forest Dormouse (Dryomys nitedula), and the only specimen of E. quercinus collected in 1965 was assigned to a non-existent settlement (Mistha 2022).

Its range contracted by 33% between 2008 and 2015 (Bertolino 2017) following on from a >50% decline in the 30 years previously (Meinig and Buechner 2012). The distribution of the Garden Dormouse was reviewed by Bertolino (2017). The species is introduced in the UK.

From the reduction in range and local extinctions in recent decades, it can be concluded that there has been a sharp decline in populations in Central, Eastern and Northern Europe. However, detailed monitoring programmes for individual populations are scarce, respectively non-existent for most parts of the range. In the south of Spain, where it was formerly abundant and expanding, it is now rare, with local extinction occurring in the Doñana National Park (Ruiz and Román 1999, Palomo and Gisbert 2002, Santoro et al. 2017). In Portugal, a population decline is possible, although the causes and magnitude of any such reduction are unknown (Cabral et al. 2005). Many of the drops in populations were over the last 50 years or so, with some of the declines more recently recorded (Bertolino 2017). Some German populations in lowlands remain stable, though others in the low mountain ranges are severely declining, such as in North Rhine Westphalia, Bavaria, Thuringia, and Saxony (Büchner et al. 2022a).

The primary habitat of the Garden Dormouse is woodland (coniferous, deciduous, and mixed) areas from the sea level up to the tree line and beyond. The species could also be found in rocky areas far from trees and in orchards, gardens, quarries, and abandoned scrub. It is less arboreal than other dormice and is often found on the ground in rocky areas, cracks in stone walls, hives and even in houses (Palomo and Gisbert 2002, Spitzenberger 2002, Bertolino 2007). In Germany, it also occurs in urban areas, including cities (Nava et al. 2022). This species could adopt communal and singular nesting reproductive strategies (Viñals et al. 2017). The generational length is approximately two years (Amori et al. 2016). The species is more carnivorous than other dormice and seems to depend on arthropods as food (Büchner et al. 2022b).

Present knowledge cannot explain the extensive regression of the Garden Dormouse's range and populations in Central and Eastern Europe. The decline is probably the result of multiple factors interacting with each other. There are indications of adverse effects related to the rarefaction of insects, the main food item, and anthropisation, but the evidence is still lacking. The decline in insect biomass significantly reduces the food supply for the species and could be an important reason for its decline (Büchner et al. 2022b). For example, intensive forestry and large-scale clearings with big machinery - e.g. after bark beetle calamities - directly destroy habitats for this species. Garden Dormice in Germany were heavily contaminated with pollutants and pesticides, including DDT and PCBs, that could reduce fecundity (Famira-Percsetich et al. 2022). Garden Dormice are also accidentally killed by rodenticides during pest control actions (e.g. forest treatment, rat control in urban areas).

It has been suggested that this dormouse might be threatened in some areas (especially Corsica) due to direct competition with the Brown Rat Rattus norvegicus (Macdonald and Barrett 1993). The species may also compete with the Edible Dormouse (Glis glis) (Meinig and Büchner 2012) though more research is needed to confirm this. In urban habitats in Germany, many animals are killed by domestic cats (Famira-Percsetich et al. 2022).

The species is considered a pest and protocolled in some orchards (e.g. in orange groves in Spain). Climate change is thought to be impacting the species; long-term studies within Doñana National Park in the southwestern corner of the Iberian Peninsula show a gradual disappearance from records as temperatures have increased (Santoro et al. 2017). As a result, and also due to the extraction of water for horticulture and tourism, the former wetland in the Doñana is suffering from a drought of historic proportions, which significantly degrades the habitat quality of the Garden Dormouse.

There is no trade known except from from some pet breeders.

The species is listed on Appendix III of the Bern Convention. There is a need to determine why the populations in the central-eastern part of the range are in decline, to monitor them, and to identify and implement appropriate conservation measures. The species is assessed as Regionally Extinct in Estonia, Latvia and Lithuania, as Critically Endangered in Czechia, Poland and Ukraine, Endangered in Flanders and Germany, and Near Threatened in Austria, Italy, Portugal and Spain.