- The Common shrew (Sorex araneus) is a small mammalian insectivore widely distributed across Europe and parts of Asia. As one of the most abundant and well-studied shrew species, it plays a crucial role in terrestrial ecosystems and has contributed significantly to our understanding of small mammal biology and evolution.
- Morphologically, S. araneus is a compact animal, measuring 55-82 mm in body length with a tail length of 32-46 mm. Adults typically weigh between 5-14 grams, with females generally being slightly larger than males. The species displays a characteristic tricolored pelage: dark brown on the back, brownish flanks, and grayish-white underparts. Seasonal changes in their appearance occur, with winter coats being darker and slightly longer than summer ones.
- A remarkable feature of S. araneus is its unique chromosomal system, which exhibits considerable geographical variation and has made it a model organism for studying chromosomal evolution. Different populations possess varying chromosome numbers and arrangements, leading to the formation of distinct chromosomal races across its range, making it particularly interesting to evolutionary biologists.
- The metabolic demands of the Common shrew are extraordinary, requiring it to feed almost continuously to maintain its high energy requirements. These shrews must consume 80-90% of their body weight in food daily. Their diet consists primarily of invertebrates, including earthworms, insects, spiders, and other small arthropods. Like other shrews, they possess mildly venomous saliva that helps immobilize their prey.
- In terms of habitat preference, S. araneus is highly adaptable but typically favors areas with dense ground cover. They can be found in woodlands, hedgerows, grasslands, and gardens, preferring damp areas with abundant leaf litter and vegetation. These shrews construct and maintain a network of surface runways through their territory, which they use for foraging and navigation.
- The species’ reproductive biology is well-documented. Breeding occurs from April to September, with females capable of producing multiple litters per year. Each litter typically contains 5-7 young after a gestation period of approximately 20 days. The young develop rapidly, reaching independence at about 22-25 days old. Life expectancy in the wild is typically 12-18 months.
- Social behavior in S. araneus is characterized by territorial aggression, with individuals maintaining and defending their own territories. The size of these territories varies seasonally and with habitat quality. During the breeding season, territorial behavior becomes more pronounced, particularly among males seeking mating opportunities.
- One of the most fascinating aspects of Common shrew biology is their ability to undergo a winter reduction in body size, known as Dehnel’s phenomenon. During winter months, their body mass, skull size, and internal organs decrease significantly, reducing their energy requirements during periods of food scarcity. This remarkable adaptation helps them survive harsh winter conditions.
- The species demonstrates complex spatial memory and navigation abilities, essential for efficiently exploiting their territory’s resources. They use both olfactory cues and spatial memory to locate food sources and navigate their environment, showing remarkable ability to remember the location of profitable feeding areas.
- Despite being abundant across most of its range, S. araneus can be vulnerable to habitat fragmentation and agricultural intensification. Changes in land management practices, particularly those affecting ground cover and invertebrate prey abundance, can impact local populations. The species serves as an important indicator of ecosystem health and plays a vital role in controlling invertebrate populations.
- Their presence in the food web is significant, as they not only control invertebrate populations but also serve as prey for various predators, including owls, kestrels, and weasels. This position makes them an important component in the transfer of energy through terrestrial ecosystems.
