535.

Mound-building Mouse

Mus spicilegus

French: Souris glaneuse / German: Ahrenmaus / Spanish: Raton de estepa

Other common names: Steppe Mouse

Taxonomy. Mus spicilegus Petényi, 1882,

Rakos Plains, Budapest, Hungary.

Due to its extensive sympatry and even syntopy with M. musculus, this species was long the object of confusion, being difficult to identify with certainty; it has now been studied using morphometric and molecular tools throughout much ofits range, and by various authors. It is a member of the subgenus Mus; the latest molecular phylogenies, such as that of H. Suzuki and K. P. Aplin from 2012, place it in the “ Mus clade”, in the subclade M. musculus, where it is the sister taxon of M. macedonicus . Monotypic.

Distribution. Endemic to SE Europe (Austria, Slovakia, Hungary, Croatia, Bosnia and Herzegovina, Serbia, Montenegro, Albania, Greece, Romania, Bulgaria, Moldova, Ukraine, and Russia).

Descriptive notes. Head-body 55-93 mm, tail 50-70 mm, ear 9-14 mm, hindfoot 14-17-5 mm; weight 9-20 g. The Moundbuilding Mouse has pale gray-brown dorsal fur that contrasting with awhite-gray belly. Thetail is as long as or slightly shorter than the body length and is unicolored. Upper incisors are notched.

Habitat. Open grassland (steppe), fallow ground, and harvested cereal fields. The Mound-building Mouse has developed a

unique system of mound-building, which allows juveniles to survive during winter. It is never found in houses. Occurs from sea level up to elevations of ¢.200 m.

Food and Feeding. Mound-building Mice are granivorous and herbivorous. In a mound, the mice can store up to 50 kg of grain and seeds. A positive correlation between the number of mice involved and the volume of the mound has been found and that there is no correspondence between the plants eaten and those used for the mound construction.

Breeding. Highly seasonal, occurring at the end of spring and summer. Juveniles born at the end of summer and in autumn spend the winter in high mounds that they build with plant matter, and delay their sexual maturity until the beginning of spring. In captivity, females have litters of 6-7 offspring, on average every 28 days. Some females born in spring were found to start breeding at 2-3 months of age, while others born later started at 6-8 months, butthis did not affect the quality and duration offertility, and no reproductive decline was observed for this second generation, which reproduced well and more quickly.

Activity patterns. The Mound-building Mouse has developed a unique strategy to survive during the cold winters of the eastern European steppes. At the beginning of autumn, kin individuals of different parental units start to build a very sophisticated mound of plant matter at the surface of harvested cereal fields or on fallow ground. This mound has an average diameter of 1-2 m (up to 4 m), is ¢.50 cm high, and may have a volume of ¢.300 1. There may be up to 20 mounds/ha. Below the mound,a storage chamber of different plant matter can contain up to 10 kg of seeds and grain. Below this chamber, nests may be situated c.60-80 cm below the soil surface, and all the structures are interconnected by a network of tunnels. Building takes 2-3 weeks, and generally involves some 11 ind/mound (up to 25/mound). These are predominantly males, mostly juveniles born in late summer and early autumn, coming from related female parents and their unrelated mates. Construction starts with the collection of plant materials piledup above ground in the chosen place, then burrows and tunnels are excavated below the mound and the excavated soil is pushed out of the mound. In the top of the mound, clumps ofclay are deposited. Temperature and humidity are higher in the nest and below the mound than in its external surface or in the soil, so it seems that these mounds offer protection against the weather and predators. After spending winter in the mound, the mice emerge and disperse in spring.

Movements, Home range and Social organization. Mound-building Mice form strong spatial pairs of one male and one female, which develop spatial avoidance of other mice. This is the only species of Mus to practice social monogamy, with a stable male— female bond. It is typically found in small groups, generally consisting of pairs of one male and one female, rarely 2-3 males with a female, or two females with a male. Polygamous females show low reproductive success. They keep exclusive home ranges during the breeding season, and both males and females are highly aggressive toward unrelated individuals. Males and females cooperate in the parental care of the young.

Status and Conservation. Classified as Least Concern on The IUCN Red List.

Bibliography. Aulagnier et al. (2009), Baudoin et al. (2005), Dobson & Baudoin (2002), Gouat & Féron (2005), Gouat, Feron & Demouron (2003), Gouat, Katona & Poteaux (2003), Holzl et al. (2011), Lafaille et al. (2014), Musser & Carleton (2005), Patris et al. (2002), Serra et al. (2012), Shimada et al. (2010), Simeonovska-Nikolova (2003), Sokolov, Kotenkova & Michailenko (1998), Suzuki & Aplin (2012), Szenczi et al. (2011), Tong Wenfei & Hoekstra (2012).