Behavior

Shrews live hidden under cover and mostly lead nocturnal lives. Their prey does not require group hunting and

Common shrews (Sorex araneus) use their long pointed snouts to unearth insects and other food. (Photo by Stephen Dalton/Photo Researchers, Inc. Reproduced by permission.)
A diving shrew diving after prey. (Illustration by Emily Damstra)

solitary foraging prevails. Predation avoidance in soricines does not depend on a long-distance escape but rather on finding shelter. Soricines live solitarily and they are territorial almost all their life. Their strict territoriality is promoted by exploitation of scarce and evenly distributed resources. Shrews establish large territories within which most foraging and nesting, as well as courtship and mating, take place. In autumn and winter, territories are maintained to maximize survivorship, and in spring and summer, to maximize reproduction. The maintenance and defense of territories is based on acoustic and olfactory communication, but direct aggression involving combat and biting is also frequent. With respect to the distribution of food resources and their predictability, two social systems of territorial behavior have been described in soricine shrews—stable and shifting territories.

The shrews with stable territories do not nest communally in order to conserve heat by huddling and they may be categorized as winter-solitary species. In spring, the territories enlarge considerably and the territories of opposite sexes may partly overlap. Different males may have different territorial behavior and mating patterns and strategies at the same time and within the same habitat. Long-distance wandering males have a lower reproductive success and they probably suffer higher predation rates. However, their movements are very important because they facilitate gene flow within the species. Courtship and mating last only a short period. Nevertheless, a female can copulate with several males during this short time and multiple paternity of pups within one litter may occur. This female strategy can reduce inbreeding. The mating system is thus rather promiscuous.

The system of shifting territories is typical for semi-aquatic shrews (Chimarrogale, Nectogale, Neomys, Sorex palustris, Sorex bendirii). In these species, the exploitation of food resources is clumped in space and undergoes unpredictable changes that

A Eurasian water shrew (Neomys fodiens) pulls a frog from a stream. (Photo by Dwight Kuhn. Bruce Coleman, Inc. Reproduced by permission.)
Northern short-tailed shrews (Blarina brevicauda) demonstrating offensive behavior in a territorial dispute. (Photo by Dwight R. Kuhn. Bruce Coleman, Inc. Reproduced by permission.)
A Eurasian water shrew (Neomys fodiens) diving. (Photo by Stephen Dalton/Photo Researchers, Inc. Reproduced by permission.)

do not favor strong and stable territoriality. Territories are not maintained for the whole life, and semi-aquatic shrews usually shift along banks of flowing waters and water reservoirs, so that their territories are changed every few weeks or months. The mating system of shrews with shifting territories is promiscuous, and the breeding females are the most aggressive members of populations. The dissimilarity of social systems of certain species (Notiosorex, Cryptotis) to those of other soricines can be related to the fact that they inhabit regions with relatively warm climates and/or with poor food resources.

Reactions of soricines with stable territories to shrews of other species, being potential competitors, are also agonistic, including the larger shrews preying upon the smaller species. In interspecific competition, behavior leading to mutual avoidance of the individuals plays a more important role than direct aggression.

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