Sorex isodon Turov 1924

13.

Taiga Shrew

Sorex isodon

French: Musaraigne de la taiga / German: Taigaspitzmaus / Spanish: Musarana de taiga

Other common names: Even-toothed Shrew

Taxonomy. Sorex isodon Turov, 1924, basin of Barguzin River, Buryatia, Siberia, Russia.

Evidence from mtDNA and nDNA sequences classifies S. isodon in the caecutiens group. Six subspecies recognized.

Subspecies and Distribution.

S.i.isodonTurov,1924—fromYeniseiRiverBasininES.i.EtoKamchatkaPeninsula.

S.i.gravestGoodwin,1933—RussianFarEast.

S.i.montanusSkalon&Raevsky,1940—AltaiMts.

S.i.princepsSkalon&Raevsky,1940—WS.i.

S.i.ruthenusStroganov,1936—N&EEurope(NSweden,NNorway,Finland,Russia,NEBelarus,andSumyregioninNEUkraine).

S. i. sachalinensis Okhotina, 1984 — Sakhalin I.

Also present in N Mongolia (Khentii Mts), NE China, and Korean Peninsula, but subspecies involved not known.

Descriptive notes. Head—body 54-86 mm, tail 37-55 mm, hindfoot 13-15 mm; weight 6-1-16-3 g. Tail of the Taiga Shrew is usually longer than 50% of head-body length;it is bicolored but sometimes only at base, with dark unicolored distal part. Pelage is almost unicolored. In juveniles, back is brown to dark brown, and belly is somewhat lighter. There is no distinct border between back, sides, and belly colors. Adults are darker, up to black-brown, with no difference in color between back and belly. Chromosomal complement has 2n = 42 and FN = 70, with 14 pairs of metacentric and submetacentric autosomes and six pairs of acrocentric autosomes. X-chromosome is large acrocentric, and Y-chromosome is small subtelocentric.

Habitat. Various habitats. The Taiga Shrew uses dark coniferous forests with substantial litter, such as cedar,fir, and spruce mountain forests, in southern Siberia. It often dominates shrew communities in fir-spruce forests with well-developed tall grasses. In the north, it prefers spruce—fir forests of riverine terraces in the north but is rarely subdominant even in these habitats. It is low in abundance and is found mostly in floodplain meadows and floodplain alder groves in the European part of the distribution. The Taiga Shrew is rare in foreststeppe and forest-tundra regions outside the forest zone and avoids tundra communities.

Food and Feeding. Earthworms and dipteran larvae found by digging through litter are the most common dietary components of the Taiga Shrew in almost all regions. Spiders and caterpillars are often present in gastric contents in southern Yakutia (= Sakha Republic) and Karelia, beetle larvae only in Karelia, and myriapods in Primorsky Krai. Adult beetles are not major parts of diets in any region.

Breeding. Reproduction of the Taiga Shrew starts 15-17 days later than in other species of shrews in the Magadan Region, southern Yakutia, central Siberia, and Karelia. A female produces up to three litters/breeding season, which ends in September. One to eleven embryos (average 7-6) were observed in pregnant females. Number of embryos/female can decrease during the breeding season and might be higher in northern regions than southern regions.

Activity patterns. Daily activity of the Taiga Shrew is multiphasic. Activity observed in the Russian Far East was the lowest compared with activities of other, even larger, species of Sorex. Daytime and nighttime activity periods are about the same duration.

Movements, Home range and Social organization. Although Taiga Shrews are solitary and have their own home ranges, sometimes home ranges of individuals agglomerate in the favorable habitats. Individual home ranges are 1200-2600 m? for overwintering males and 700-1400 m* for immature males in Karelia.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Taiga Shrew is common and dominates shrew communities in mountain dark conifer forests of southern Siberia. It is low in abundance in the European part of its distribution and is consequently on several Regional Red Lists (Karelia, Novgorod, and Ryazan regions).

Bibliography. Bekenov et al. (1985), Bobretsov (2016), Churchfield & Sheftel (1994), Churchfield et al. (1999), Dokuchaev (1990), Gureev (1979), Ivanter(1975), Ivanter & Makarov (2001), Kalinin et al. (1998), Mishta (2011), Nesterenko (1999), Okhotina (1974, 1984), Revin (1989), Shchipanov et al. (1998), Sheftel (1983), Sulkava (1990c), Zima et al. (1998).