|Common shrew range|
The common shrew (Sorex araneus), also known as the Eurasian shrew, is the most common shrew, and one of the most common mammals, throughout Northern Europe, including Great Britain, but excluding Ireland. It is 55 to 82 millimetres (2.2 to 3.2 in) long and weighs 5 to 12 grams (0.2 to 0.4 oz), and has velvety dark brown fur with a pale underside. Juvenile shrews have lighter fur until their first moult. The common shrew has small eyes, a pointed, mobile snout and red-tipped teeth. It has a life span of approximately 14 months.
Shrews are active day and night, taking short periods of rest between relatively long bursts of activity.
Common shrews are found throughout the woodlands, grasslands, and hedgelands of Britain, Scandinavia, and Eastern Europe. Each shrew establishes a home range of 370 to 630 m² (440 to 750 yd²). Males often extend the boundaries during the breeding season to find females. Shrews are extremely territorial and will aggressively defend their home ranges from other shrews. They make their nests underground or under dense vegetation.
The common shrew's carnivorous and insectivorous diet consists of insects, slugs, spiders, worms, amphibians and small rodents. Shrews need to consume 200 to 300% of their body weight in food each day in order to survive. A shrew must eat every 2 to 3 hours to achieve this goal. A shrew will starve if it goes without food for more than a few hours. They do not hibernate in the winter because their bodies are too small to store sufficient fat reserves and as they have a short fasting duration.
Common shrews have evolved an amazing adaptation to survive through the winter. Their skulls shrink by nearly 20% and their brains get smaller by as much as 30%. Their other organs also lose mass and their spines get shorter. Their total body mass drops by about 18% as a result. When spring arrives, they grow until they reach roughly their original size. Scientists believe that dropping temperatures trigger their bodies to breakdown bones and tissues and absorb them. As temperatures start to rise with the onset of spring, their bodies start to rebuild the lost bones and tissues. This significantly reduces their food requirements and increases their chances of survival in the winter.
The common shrew breeding season lasts from April to September, but peaks during the summer months. After a gestation period of 24 to 25 days, a female gives birth to a litter of five to seven babies. A female rears two to four litters each year. The young are weaned and independent within 22 to 25 days.
Young shrews often form a caravan behind their mother, each carrying the tail of its sibling in front with its mouth.
The chromosome number (karyotype) of Sorex araneus varies widely, with a number of distinct "chromosomal races" being present over the species' range. One such race was described in 2002 as a new species, S. antinorii. This an example of chromosomal polymorphism (chromosomal variability as a result of chromosome fusions or disassociations).
Protection and population
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- Hutterer, R.; Amori, G. & Kryštufek, B. (2008). "Sorex araneus". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved 31 December 2011.
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- Saarikko, Jarmo (1989). "Foraging behaviour of shrews". Annales Zoologici Fennici. 26 (4): 411–423. JSTOR 23734695.
- British Wildlife. London: Collins. 2002. p. 402. ISBN 0-00-713716-8.
- Churchfield, Sara; Rychlik, Leszek; Taylor, Jan R. E. (2012-10-01). "Food resources and foraging habits of the common shrew, Sorex araneus: does winter food shortage explain Dehnel's phenomenon?". Oikos. 121 (10): 1593–1602. doi:10.1111/j.1600-0706.2011.20462.x. ISSN 1600-0706.
- Stetka, Bret. "Small-Minded Strategy: The Common Shrew Shrinks Its Head to Survive Winter". Scientific American. Retrieved 2017-10-24.
- Lázaro, Javier; Dechmann, Dina K.N.; LaPoint, Scott; Wikelski, Martin; Hertel, Moritz (2017-10-23). "Profound reversible seasonal changes of individual skull size in a mammal". Current Biology. 27 (20): R1106–R1107. doi:10.1016/j.cub.2017.08.055. ISSN 0960-9822. PMID 29065289.
- "BBC Science and Nature: Animals". Retrieved 11 September 2009.
- Polymorphism: when two or more clearly different phenotypes exist in the same interbreeding population of a species. Ford E.B. 1975. Ecological genetics, 4th ed.
- White M.J.D. 1973. The chromosomes. Chapman & Hall, London. p169
- Wildlife and Countryside Act 1981 S11, Sch 6
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